Following a 26 day stretch in which the temperature at Downtown Los Angeles was below normal 25 of the days, and several lowest maximum temperature records were set around the area, temperatures have soared, and record high temperatures for the date have been recorded at several locations.

On June 30, Downtown Los Angeles ended the water year about 8% above normal. Some stations in the Los Angeles area recorded more than this and some less. There was a wide range of values. For example, Long Beach Airport was about 20% above normal and Santa Barbara Airport about 23% above; but Camarillo Airport reported 31% below normal rainfall. Here's an AHPS graphic showing the percent of normal precipitation in California and the Southwest for the year ending July 1 at 12z.

Equatorial Pacific SSTs have generally continued to cool. According to the CPC's Weekly ENSO Update, issued July 12, the latest weekly SST departures were -1.3°C (Niño1+2), -1.0°C (Niño 3), -0.8°C (Niño 3.4), and -0.4°C (Niño 4). According to the CPC, La Niña conditions occur "when the monthly Niño3.4 OISST departures meet or exceed -0.5°C along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months."

Reflecting the transition from El Nino to La Nina conditions, the Multivariate ENSO Index (MEI) for May-June experienced an unprecedented drop for the time of year, decreasing nearly 1 standard deviation to a value of -0.41. In addition, the Global Wind Oscillation (GWO) has orbited about -2 SD down on the La Nina side of the phase space plot, and with the atmosphere in a generally low momentum state, may be in that neighborhood for a while.

The most recent IRI ENSO Update, released July 15, projects "an approximately 80% probability for continuing La Niña conditions, and a 20% probability for returning neutral ENSO conditions. "

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Equatorial Pacific SSTs have continued to cool and TAO/TRITON data shows -1.0°C or greater anomalies extending from 95°W to beyond 150°W. According to the CPC's Weekly ENSO Update, issued June 21, the latest weekly SST departures were -0.7°C (Niño1+2), -0.6°C (Niño 3), -0.5°C (Niño 3.4), and 0.0°C (Niño 4). An anomaly of -0.5°C in the Niño 3.4 region is the threshold for La Nina conditions.

The Global Wind Oscillation (GWO) has spiraled well into La Niña territory. The global relative atmospheric angular momentum anomaly is at its lowest value since March 2008, during the La Niña of 2007-2008.

Based on equatorial Pacific SSTs, section plots, tradewinds and cloudiness; and the GWO and AAM; a transition to La Nina conditions appears to be underway.

It looks like Downtown Los Angeles (USC) will likely end the July 1 - June 30 water year having recorded 16.36 inches of rain. This is more than an inch above the 1971-2000 annual climate norm of 15.14 inches.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Woodland Hills (Pierce College) topped the 90° mark for the first time this year Memorial Day weekend, and after cooling a few degrees during the week, temperatures are back into the 90's this afternoon. A quick look at temps around the area shows temps near 70 on the coast; 80's to 90's in the valleys, and triple digits in the deserts.

Reflecting the transition to ENSO neutral conditions, the Multivariate ENSO Index (MEI) for April-May declined to 0.54. According to the CPC's Weekly ENSO Update, issued June 1, the latest weekly SST departures are -0.6°C (Niño1+2), -0.4°C (Niño 3), -0.2°C (Niño 3.4), and 0.4°C (Niño 4).

In his May 2010 MEI discussion Klaus Wolter projected the probability of a La Nina event emerging by the end of 2010 at roughly 50%. In it's May 2010 ENSO Quick Look, the International Research Institute for Climate and Society (IRI) put the probability of La Nina conditions from the August-October season through the remainder of 2010 at 42%. We'll see!

Downtown Los Angeles (USC) has recorded 16.36 inches of rain since the water year began July 1. This is more than an inch above the 1971-2000 annual climate norm of 15.14 inches. The water year ends June 30. Climatology and current forecasts suggest it is unlikely that this total will change by more than a hundredth or two before the end of the month.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

During the last month the 2009-10 El Niño has essentially transitioned to ENSO neutral conditions. Over the course of the event, the Multivariate ENSO Index (MEI) peaked in JAN/FEB at 1.5, and the Oceanic Nino Index (ONI) peaked in NDJ at 1.8. The mean 5-day averaged November 1 to March 31 relative AAM anomaly was 0.304. The strongest El Niño forcing appeared to have occurred in late January after the active phase of the Madden-Julian Oscillation (MJO) enhanced El Nino convection in the equatorial Pacific. Here's a chart comparing the 2009-10 El Niño to 17 other warm ENSO episodes that have occurred since 1950.

Dynamical and statistical ENSO model forecasts suggest the possibility that equatorial Pacific SSTs will continue to decline, leading to weak to moderate La Niña conditions by late Summer or Fall. A return to El Niño conditions does not appear likely, but cannot be ruled out. In his May MEI discussion, Klaus Wolter points out that the 1957-1958 El Nino, an analog to the 2009-2010 El Niño, rebounded after dropping into neutral territory.

Downtown Los Angeles (USC) has recorded 16.31 inches of rain since the water year began July 1. This is more than an inch above the 1971-2000 annual climate norm of 15.14 inches. Recent runs of the GFS and ECMWF show a negatively tilted trough deepening and moving onshore early next week. At this point it looks like there's a pretty good chance of showers north of Pt. Conception, but only a slight chance down here. We'll see!

Update 05/18/10. Stations in the Los Angeles area generally recorded under a tenth of an inch from this system. Some isolated totals of about 0.25 inch were recorded in Ventura and Santa Barbara county, and Rocky Butte in San Luis Obispo recorded 0.48 inch. Here is an archived copy of a NWS Public Information Statement with some rainfall totals from around the area.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A classic cold front associated with a cold upper level low and Pacific trough pushed through Southern California overnight Sunday, producing rain at the lower elevations and snow at the higher elevations. Scattered convective showers and isolated thunderstorms followed in the wake of the front as the low and trough slowly moved onshore. TV news reports showed marble sized hail produced by a strong cell in the eastern San Fernando Valley.

Downtown Los Angeles (USC) recorded 0.91 inch of rain for the storm, bringing the water year total to 16.17 inches, which is more than an inch above the 1971-2000 annual climate norm of 15.14 inches*. Here's an archived copy of a NWS Public Information Statement with some rainfall totals from around the area.

The additional rainfall puts Downtown Los Angeles at 1.51 inches for the month of April, well above the climate normal of 0.83 inches. The normal amount of precipitation for May is 0.31 inches, and for June is 0.06 inches. Although the current El Nino appears to be in decline, convection is still enhanced in a broad area of the western and central equatorial Pacific, and the GWO, MEI, and ONI all indicate the continued presence of El Nino. This could result in more active Spring weather than usual. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

*The average annual rainfall for Los Angeles of 15.14 inches is computed on a calendar year basis for the 30 year period 1971-2000. Technically it is not a water year average, but by convention it is used as a reference for water year rainfall. For details about how normal temperature and precipitation values are computed, see CLIMATOGRAPHY OF THE U.S. NO. 81 - Monthly Station Normals.

This week's Pacific system produced more rain in Southern California than recent similar troughs. The front associated with the system stalled as it approached the Los Angeles basin, and the low level inflow and jet dynamics helped sustain rain rates as the front dissipated.

Downtown Los Angeles (USC) recorded 0.60 inch of rain, bringing the water year total to 15.26 inches, which is above the 1971-2000 annual climate norm of 15.14 inches*. Here's an archived copy of a NWS Public Information Statement with some rainfall totals from around the area.

The water year ends June 30, so we still have a few weeks to add to our rainfall total. Los Angeles rainfall was below normal for the month of March, but we're already above normal month to date for April and it looks like more wet weather could be on the way. Recent runs of the GFS and ECMWF have been suggesting another system will affect Southern California the Sunday evening to Monday timeframe, and also project the possibility of another system midweek. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

*The average annual rainfall for Los Angeles of 15.14 inches is computed on a calendar year basis for the 30 year period 1971-2000. Technically it is not a water year average, but by convention it is used as a reference for water year rainfall. For details about how normal temperature and precipitation values are computed, see CLIMATOGRAPHY OF THE U.S. NO. 81 - Monthly Station Normals.

After peaking at a standardized relative AAM anomaly of 2.21 around February 5, 2010, the Global Wind Oscillation (GWO) has plunged 3 SD in relative AAM to a value of -0.90. This is the lowest value of relative AAM anomaly since mid October, 2009. Much of the loss in AAM was from the mid latitudes of the NH. From the week of February 22-28 to March 19-25, 7-day averaged 250 mb Zonal Mean Zonal Winds decreased from about 43 m/s at 30°N to 33 m/s at 30°N-45°N. The decrease in relative AAM reduced the likelihood of an extended and southward displaced North Pacific Ocean jet, and associated Southern California El Nino impacts.

In fact, there has been no measurable precipitation at Downtown Los Angeles (USC) since March 6, 2010. Los Angeles rainfall is now 2.23 inches below normal for the month of March, and only 1.15 inches above the water year norm for the date.

In the last week there has been an increase in relative AAM from about 40°N to 50°N. The GWO and AAM appears to have bottomed out and cyclical subseasonal processes may be working to revitalize Western Pacific convection and El Nino related forcing. If the GWO continues its current orbit, relative AAM would be expected to increase in the 6-10 day period.

The GFS and ECMWF have been showing a strong Pacific jet and trough affecting the West Coast next week. There are significant differences in the GFS and ECMWF model solutions, and although 5-day model performance has been good recently, performance often suffers during seasonal transitions. This morning's 12z GFS puts the initial focus of the event in the Pacific Northwest early in the week. Precipitation is forecast to spread into Northern and Central California, and finally Southern California, as the week progresses, and the trough deepens and moves onshore.

It's way too early to say how this system will affect Southern California. Many processes are in play that could affect the amount of precipitation here, pro or con. Yesterday afternoon's 00z ECMWF appeared to project a wetter solution for Southern California than this morning's 12z GFS, with the upper low and trough evolving a little more to the west. It does look like there is the potential for heavy snow in the Sierra. We'll see!

Update 04/03/10. The frontal band and upper low associated with the trough that moved through the area overnight Wednesday into Thursday produced some showers and some spectacular clouds in the Los Angeles area. The bulk of the precipitation occurred from Central California north into the Pacific Northwest. The upper low stayed offshore as it moved down the coast and past the Los Angeles basin. Avalon and some mountain locations recorded more than 0.1 inch of precipitation, but generally amounts south of Pt. Conception ranged from a trace to few hundredths. Here's an archived copy of a NWS Public Information Statement with some rainfall totals from around the area. A similar system is forecast to produce some rain in Los Angeles area Sunday night. BUFKIT analysis of 18z NAM data for Van Nuys projects about 0.4 inch of precipitation. The 09z SREF shows a high probability of measurable rain, but a sharp decrease in the probability of more than 0.1 inch/day south of Pt. Conception. We'll see!

There was an interesting lenticular wave train northwest of Los Angeles earlier this month. The situation was peculiar because the wind at nearly all levels at that time was from the northwest, and the wind forming the wave clouds appeared to be from the north-northeast. The tops of the wave clouds were being sheared by winds blowing from the northwest (left to right). An ARL NAM-12 based wind profile for the area on March 10 for 06z, shows a possible source of the winds that produced the waves, as well as the shear. Here's an animated series of NRL satellite photos showing the complex wind and wave pattern at the time.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

As forecast, an energetic upper low skirted the Los Angeles area yesterday on its way south into northern Baja, Mexico. As the low moved south, a vorticity lobe spinning around the low arced into the Southern California coast, producing rain, thunderstorms, waterspouts, and blustery winds.

Rain amounts were variable, generally ranging from about 0.25 inch to 0.75 inch around the Los Angeles area. Indicative of the convective nature of the precipitation, Downtown Los Angeles (USC) recorded 0.42 inch, while a few miles away LAX recorded only 0.18 inch for the storm. The water year total for Downtown Los Angeles now stands at 14.66 inches -- only 0.48 inch less than the annual norm of 15.14 inches. Here is an archived copy of NWS Public Information Statement with some more rainfall amounts for this rain event.

Reflecting the enhancement of El Niño by the MJO at the end of January, the Multivariate ENSO Index (MEI) for January-February has increased to 1.5. As discussed by Klaus Wolter, MEI originator, this is the highest value of the Jan-Feb MEI since the strong El Niño of 1997-1998, and the fifth highest MEI value for Jan-Feb since 1950. This places the El Nino of 2009-10 in the top 10% of MEI rankings for the season since 1950, and above the "strong" El Niño threshold, as measured by the MEI. Here is a chart comparing the current El Niño to others since 1950.

The increase in the MEI corresponds to the increase in relative AAM since mid January and underscores the potential role of the Global Wind Oscillation (GWO) in assessing the response of the atmosphere to El Niño. It also reinforces the notion that the El Niño phenomena is more than just warm SSTs in the central equatorial Pacific. As we've seen several times in recent years, warm SST anomalies in the Niño 3.4 region alone are not sufficient for evaluating an El Niño and its potential impacts.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Tuesday's trough was even more feeble than expected south of Santa Barbara, barely managing to wet the streets and generate an official "trace" of rain in the Los Angeles area. Wednesday's upper low dug a little further south than expected, resulting in some moderate showers. Rainfall amounts were variable, generally ranging from a few hundredths in the basin to 0.25 inch or so at some mountain locations . Here are archived copies of NWS Public Information Statements with some rainfall amounts for Tuesday's trough and Wednesday's upper low.

Downtown Los Angeles (USC) recorded 0.06 inch of rain Wednesday, bringing the water year total (July 1-June 30) to 14.24 inches, which is 3.05 inches above normal for the date.

Another finicky upper low may produce some rain in Southern California this weekend. Just how much depends on the behavior of the low and it's proximity to the Southern California coast. If the low track is too far offshore, rainfall amounts could be dramatically reduced. This is well illustrated by 09z SREF plot showing the forecast probability that precipitation will exceed 0.1 inch for the 24 hr. period ending Saturday at 7:00 p.m. BUFKIT analyses of today's 18z NAM data for Santa Barbara, Van Nuys and LAX all produce about 0.3 inch of rain, mostly on Saturday.

Update 03/05/10 8:00 a.m. The models continue to have difficulty with the timing and precipitation amounts for this weekend's storm. This isn't surprising since small changes in the track of the upper low, the amount of moisture entrained, and other factors could have a big effect on the amount of rain in a particular region. Yesterday afternoon's run of the NAM generated nearly an inch of rain at Van Nuys, but this morning's 12z run of the NAM is back down to the neighborhood of 0.3 inch. Today's 09z SREF suggests the highest precipitation amounts may occur to the south of Los Angeles. Here's an SREF plot of the probability that precipitation will exceed 0.25 inch for the 24 hr. period ending 10:00 a.m. Sunday. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A primary frontal band, secondary frontal band, and upper low associated with a strong Pacific storm system produced periods of heavy rain in Southern California on Saturday. Rainfall totals for the system generally ranged from about 1.0 to 2.0 inches, with somewhat higher amounts recorded at a few mountain locations. Here is an archived copy of a NWS Public Information Statement with some precipitation totals from around the area.

Downtown Los Angeles (USC) recorded 0.80 inch of rain for the storm, bringing the water year total (Jul 1-Jun 30) to 14.18 inches, which is 3.25 inches above normal. Saturday, Burbank set a new rainfall record for the date of 1.6 inches.

The weather forecast for the Los Angeles area this week looks like a near repeat of last week, with a chance of showers mid-week, and then a possibility of a somewhat stronger storm for the weekend.

Just 24 hours before a trough is forecast to produce a chance of showers in the Los Angeles area, the models are still having difficulty with the forecast. The nature of the system is the culprit -- the evolution of the trough and precise track of a following upper low is far from certain. Today's 09z SREF suggest a high probability (70%-90%) of very light rain (>0.01 inch) for the 24 hr. period ending 7:00 a.m. Wednesday morning, but south of Pt. Conception there is a rapid decrease of the probability of more than 0.1 inch of precipitation over the same period.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A weakening frontal band produced some light rain in Southern California yesterday afternoon and evening. Precipitation amounts in the Los Angeles area ranged from a trace to a few hundredths of an inch. Amounts were higher to the north, closer to the surface low. A few stations in Santa Barbara and San Luis Obispo counties recorded more than 0.5 inch and some recorded more than an inch. Here is an archived copy of a NWS Public Information Statement with some precipitation totals from around the area.

Today, a much stronger Pacific storm system begins to impact the West Coast, with the highest precipitation totals forecast for Northern California and the Sierra Nevada. BUFKIT analysis of this morning's 12z NAM data for Van Nuys generates about 1.3 inch of rain, beginning late Friday night and continuing into Saturday afternoon. The 18z NAM run starts the rain a little earlier Friday night, and extends the period of precipitation into Saturday evening. It produces about 1.8 inch of rain at Van Nuys over the period. Today's 09z SREF indicated a probability of about 50%-70% that precipitation in the Los Angeles area would exceed 0.5 inch for the 24 hr. period ending Saturday afternoon at 4:00 p.m. Precipitable water values approaching an inch and strong southerly low level inflow could produce higher rain rates and precipitation totals on south to southwest facing foothill and mountain slopes.

Since being reinforced by a strong MJO at the end of January, El Niño convection has remained active in the Central Pacific (animation). In terms of relative atmospheric angular momentum (AAM), the atmosphere's response is the strongest since the El Ninos of 1997-1998 and 2004-2005. Average AAM for our rain season (November to date) has increased from -0.046 at the beginning of the year to 0.341 as of February 23. This El Nino Comparison Chart shows how this El Niño compares to others since 1950.

So far this rain season, Downtown Los Angeles (USC) has recorded above average rainfall every month, except for November. And November's rain came early -- in October.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Last night's weak Pacific system had its moments, and managed to produce precipitation amounts ranging from about 0.1 inch to 0.25 inch in the Los Angeles area. Here is a NWS Public Information Statement with some precipitation totals. Downtown Los Angeles (USC) recorded 0.14 inches for the storm, increasing the water year total to 13.34 inches. The is 3.58 inches above normal for the date.

A moisture-starved trough on the downstream side of a pinched upper level ridge over the West Coast is forecast to dig southward and could produce some additional precipitation tomorrow. Today's 09z SREF indicated a probability of about 30%-50% that precipitation in the Los Angeles area would exceed 0.1 inch for the 24 hr. period ending Monday morning at 4:00 a.m. The forecast probability that it would exceed 0.25 inch over the same period is about 10%-30%.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Yesterday's cold upper level low behaved about as expected, following a track just off the coast. Because of the convective nature of the system, rainfall amounts varied from under 0.25 inch to over 1.0 inch in some foothill and mountain locations. About a foot of snow was reported at the mountain resorts. Here is a NWS Public Information Statement with precipitation totals from around the area. Downtown Los Angeles (USC) recorded 0.44 inches for the storm, increasing the water year total to 13.2 inches. The is 4.78 inches above normal for the date.

Compared to the AHPS 90 Day Precipitation map from about 40 days ago, a fairly typical El Niño precipitation pattern has emerged in the West. Medium range models are projecting about a 7-10 day break in what has turned out to be a busy rainy season in Southern California. Assuming these forecasts verify, such a break could not come a better time for those threatened by mudslides and debris flows. The recent enhancement of El Niño convection by the MJO, and the ongoing phase 6-7-8 transition of the GWO might have resulted in a wetter pattern, and this has occurred in similar circumstances in past El Ninos.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Wet antecedent conditions and heavy rain early this morning combined to amplify the amount of runoff from our latest Winter storm. In addition to localized street flooding, mud and debris flows have occurred in the vicinity of the Station Fire burn area. The trough associated with the system, and a second frontal band are moving onshore this afternoon, and are producing some additional rainfall in the Los Angeles area. Please refer to www.weather.gov/losangeles for the latest warnings and weather information.

Yesterday's runs of the NAM/WRF did a pretty good job of forecasting the area of enhanced precipitation that developed overnight in Southern California. BUFKIT analysis of 12z NAM data from yesterday generated about 2.4 inches of precipitation at KLAX for the 24 hr. period ending early this morning. According to preliminary NWS data, as of 10:00 a.m. LAX had recorded 2.31 inches for the storm, and Downtown Los Angeles (USC) had recorded 2.84 inches. The water year total rainfall for Los Angeles is now about 5 inches above normal. Here is a NWS Public Information Statement with rainfall totals from around the area. (Link will be updated as revised totals become available.)

The recent enhancement of El Nino convection in the equatorial Pacific by the Madden-Julian Oscillation (MJO) has triggered a strong atmospheric response. A Global Wind Oscillation (GWO) phase space plot shows large increases in relative atmospheric angular momentum (AAM) and AAM tendency. As a result of this increase, the average relative AAM anomaly for the rain season to date is now positive. As mentioned in this post from December 2009, relative AAM is correlated with rain season precipitation in Southern California. This suggests an increased likelihood of wet weather in Southern California in the medium range outlook period.

So what happens next? The ECMWF and GFS projections have not been particularly consistent. At the moment, it looks like a shortwave trough could affect Southern California in the Tuesday evening or Wednesday timeframe and then again Friday. We'll see how the week develops.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Following six consecutive days with rain, skies are partly cloudy today and Southern Californians can finally get out and enjoy a little sunshine. According to NWS data, Downtown Los Angeles (USC) received 4.58 inches of rain from the series of storms, bringing its water year total to 9.71 inches, which is 3.57 inches above normal for the date.

The Los Angeles/Oxnard office of the NWS has released a Public Information Statement with rain and snowfall totals for the 6 day period 10:00 a.m. Sunday morning to 10:00 a.m. today (Saturday).

Computer projections have been inconsistent, but it looks like we'll probably get some more rain early in the week. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

The fifth and final system of the series that began Sunday brought thunderstorms, damaging winds, record low pressure, heavy rain and snow to Southern California yesterday. The unusually large trough associated with the system covered most of the northeastern Pacific yesterday, and unsettled weather is expected today as it continues to move onshore.

Very strong wings, possibly a tornado or thunderstorm downburst, felled trees and damaged structures in Ventura and Santa Barbara. Record rainfall for the date was recorded at Santa Maria, Palmdale, and Lancaster, but more extraordinary, new all-time records for lowest barometric pressure were set at several locations in the Los Angeles area. Note: The NWS documented an EF-0 tornado in Ventura (3Mb PDF).

Here are some preliminary rainfall totals from around the area, compiled by the NWS, for the period 10:00 p.m. Tuesday to 10:00 p.m. this evening. Note that this combines rainfall from system #4 on Wednesday, and our current Thursday-Friday system. And here's an NWS Public Information Statement with some impressive snowfall totals for the week. Wow -- Mt. Baldy got 7 feet of snow! (Updated 01/23/10)

As of yesterday, Downtown Los Angeles (USC) has received 4.21 inches of rain from the series of storms, bringing its water year total to 9.34 inches, which is 3.44 inches above normal. Over the week, the Sierra Nevada has received several feet of snow, and the statewide average snowpack is now above normal.

Please refer to www.weather.gov/losangeles for the latest warnings and weather information.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

In a classic case of "be careful what you wish for," Southern California has been awash in a series of storms that rival those of the biggest El Nino years. Coming on top of the rain we've already recorded this week, today's and Thursday's systems appear likely to deliver a combination punch with potentially serious consequences.

Yesterday's vigorous system was characterized by scattered thunderstorms, heavy downpours, and damaging winds. Rainfall amounts generally ranged from about 0.5 inch to 1.0 inch, with some isolated higher amounts. Here's an archived copy of NWS Public Information Statement with preliminary rainfall totals for the period 5:00 a.m. to 4:00 p.m. Tuesday.

Today's frontal system, the fourth in the series since Sunday, is producing heavy rain, strong winds, and the possibility of thunderstorms. More rain is expected than resulted from yesterday's storm. BUFKIT analysis of 18z NAM data for Van Nuys (VNY) indicates about 2 inches of rain today and tonight, with generalized rain rates peaking at about 0.4 inch/hour. Higher localized rainfall rates could occur in the vicinity of thunderstorms. Here is an archived copy of a NWS Los Angeles Quantitative Precipitation Statement with more detailed information.

Unlike previous systems this week, Thursday's system is forecast to develop a surface low west of Pt. Conception. According to the WRF forecast a multi-centered surface low will develop and deepen into a 972 mb low west to northwest of Pt. Conception. In addition to the usual dynamics associated with such a low, a very strong jet is forecast to be in a position overhead that would maximize system dynamics. The formation of a surface low could also slow the progress of the system, potentially increasing precipitation totals.

Please refer to www.weather.gov/losangeles for the latest warnings and weather information.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

So many systems are moving through Southern California so fast, I thought I better check some satellite images and make sure I had my count right. Here's a NRL GOES Day/Night image from Sunday afternoon that shows system #1 moving into Southern California, and systems #2 and #3 out in the Pacific.

Then here is a NRL GOES Day/Night image from midday yesterday (Monday) that shows system #2 hammering Southern California. The combined rainfall totals from system #1 and system #2 are listed in this archived copy of NWS Public Information Statement issued this morning.

Today's system is number three in the series that started Sunday afternoon. Intellicast.com composite radar shows the N-S aligned frontal band moving onshore this morning. Current QPF forecasts suggest precipitation amounts ranging from about 0.75 inch to 1.5 inches with higher amounts possible in the foothills and mountains, or in heavy downpours associated with thunderstorms. This system is colder and more convective than previous systems in the series, so precipitation amounts may vary widely.

System #3 is a transitional system, as a large upper and lower level low complex and circulation develops in the Northeastern Pacific. The resulting system #4-5 looks to be the culminating event of the series, and is forecast to produce rain on Wednesday, and then again Thursday into Friday. BUFKIT analysis of 12z NAM data generates more than 3.5 inches of rain in the central San Fernando Valley from Wednesday morning through Friday afternoon. If the NAM forecast verifies, even higher totals could occur in orographically favored foothills and mountain locations.

Please refer to www.weather.gov/losangeles for the latest warnings and weather information.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

The first of several systems forecast to affect Southern California this week moved through the area overnight, resulting in generally moderate rainfall. Precipitation amounts in the Los Angeles area generally ranged from about 0.3 inch to 1.0 inch, with somewhat higher totals in Ventura and Santa Barbara counties. Here's an archived copy of NWS Public Information Statement with preliminary rainfall totals through 4:00 a.m. this morning.

All eyes now turn to the second system of the series, currently moving onshore. This system is expected to produce more rain, higher rain rates, stronger winds, and a higher likelihood of significant weather impacts than last night's system.

Please refer to www.weather.gov/losangeles for the latest information.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

After nearly two weeks of idyllic days with temps in the 70's and 80's, it rained in Southern California last night and into this morning. But today's rain is just a precursor. Just a little reminder that it's the rainy season in Southern California, and more rain is on the way -- possibly a lot more rain.

Skies will start to clear later today, and temps are forecast to be back into the 70's tomorrow. But the dry weather won't last. For several days forecast tools have been projecting a major pattern change -- to a wet pattern more like what might be expected in January of an El Nino year.

Today's Climate Prediction Center 6-10 day precipitation outlook indicates a 70% probability that precipitation will be above normal in Southern California for the period January 19-23, and the 8-14 day precipitation outlook indicates a 60% probability that precipitation will be above normal for the period January 21-27.

As part of its analysis, the CPC now uses historical analogs with 500 hPa patterns similar to the current forecast. In the 6-10 day forecast period the 10 most similar analogs produced above average precipitation in Southern California 9 out of 10 times. In the 8-14 day period the 10 closest analogs produced above average precipitation 6 or 7 times out of 10. Also of note, many of the analog cases with the most similar 500 hPa patterns are from wet El Nino years, such as 1958, 1978, 1983, 1992, 1995, and 1998.

Late in the weekend, around Sunday evening, the first of these potentially strong systems is expected to move onshore. Additional impulses and systems are forecast to follow in quick succession, driven by a fast moving zonal flow and strong jet stream. If current computer projections validate, the wet pattern could continue through the end of January. If precipitation totals approach what is forecast over the period, a host of rain related impacts are a possibility. We'll see.

Update January 15, 2010. PDF of slides from NWS Los Angeles/Oxnard Weather Briefing "Significant Storm Impacts For Southern California Next Week" by Eric Boldt Warning Coordination Meteorologist. Presented on January 14, 2010. Please refer to www.weather.gov/losangeles for the latest information.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Related post: How Does the El Nino of 2009-10 Compare to Other Warm ENSO Episodes Since 1950?

In terms of typical El Nino impacts, Southern California is still waiting. If you squint your eyes and have a good imagination, there is a hint of an El Nino rainfall pattern on the West Coast, but rainfall over much of our area ranges from a little below normal to a little above.

Including Wednesday's meager rainfall, Downtown Los Angeles is now about 1.1 inch above normal for the water year. That sounds great, but is a little deceptive. Some stations are well below normal and some well above. For example, Camarillo is 1.4 inches below normal, and Santa Barbara 2.3 inches above. According to the AHPS precipitation map, some mountain areas of Santa Barbara have had 200% of normal rainfall the past 90 days.

As expected, the Global Wind Oscillation (GWO) did orbit up into the positive AAM side of the phase space; but as feared, Indian Ocean/West Indonesian convection appears to have (once again) quashed the positive response. The average relative AAM anomaly for the period November 1 to December 29 remains slightly negative, and total global relative angular momentum is just about where it was at the beginning of November.

Updated January 2, 2010. Recent runs of the GFS show the Pacific jet extending and then collapsing into another trough off the West Coast during the week. This seems a little late to be directly related to the recent GWO phase 8-1 transition. A continued orbit of the GWO to phase 2 and 3 would be expected to shift the jet north and could result in another highly amplified wicked ridge of the west. Today's 18z run of the GFS plows the trough into a resistant ridge with most of the energy going up and over the ridge. The 12z ECMWF splits the trough and attempts to bring part of it in under the ridge. We'll have to see how things develop during the week.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Induced by MJO enhanced convection in the West Pacific, a change in pattern is underway which is expected to produce significant rainfall in California over the next week.

The first shortwave is forecast to ride down the east side of a very high amplitude blocking ridge along the West Coast, dig offshore on Sunday evening, and merge with another shortwave as the westerlies try to undercut the ridge on Monday.

It's an extraordinarily complex scenario, and just how it will play out is hard to say. A BUFKIT analysis of 18z NAM data generates about 1.2" at LAX and about 1.5" at VNY. Relatively strong south to southwest inflow is forecast and would be expected to produce higher precipitation amounts in favored foothill and mountain locations.

Mid-week the westerlies are forecast to break through underneath the ridge, opening the door to more wet weather.

Update 12/08/09 5:00 p.m. The best dynamics worked out to be south and east of Los Angeles county, and as this AHPS graphic shows that's where the most precipitation was recorded. But the Los Angeles area still received it's fair share of precipitation and managed to do so without inundating the areas burned in the San Gabriel Mountains by the Station Fire. This was due in part to the generally moderate rainfall rates and the low snow level. This Intellicast.com composite radar image from 2:30 Monday afternoon shows the jet enhanced precipitation to the south of the Los Angeles basin, and the frontal band north of the basin.

Over the course of the storm Downtown Los Angeles (USC) recorded 0.95 inches, bringing the water year total to 2.28 inches, which is about 0.75 inches above normal for the date. Here's an archived copy of a NWS Public Information Statement with rainfall -- and snowfall -- totals from around the area.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Drier than average weather in the Southwestern U.S., and wet weather in the Pacific Northwest in recent weeks has some folks wondering if the 2009-2010 El Niño is going to be another one of the quirky, underachieving El Niños we've been seeing this decade.

For much of September and October, the primary area of equatorial convection in the Eastern Hemisphere was in the Central Pacific, just west of the dateline. Convection was suppressed in the Indian Ocean. Such a pattern is consistent with El Niño.

Enhanced convection centered at about 160E in early October may have helped to extend the Pacific jet following an East Asian mountain torque event around October 5. This in turn may have contributed to an atmospheric river precipitation event in California October 13-14, 2009.

At that time it looked like we might finally be off and running with a "real" El Niño event. Particularly because during October equatorial Pacific SSTs and heat content anomalies increased dramatically. Theses increases were the result of of a strong Westerly Wind Burst (WWB), an associated downwelling Kelvin wave, and diminished tradewinds,

However -- and I think I hear Ed Berry's Rottweiler growling -- beginning in mid October, strong convection developed in the Indian Ocean. This essentially neutralized El Niño, and perhaps contributed to the La Nina like precipitation pattern we've been experiencing along the west coast of the U.S.

Indicative of the ocean-atmosphere issues, relative Atmospheric Angular Momentum (AAM) has been negative since early September, and the Global Wind Oscillation (GWO) has remained on the La Nina side of the GWO phase space.

Does this mean we've had an El Niño false alarm?

I wouldn't put away my rain gear just yet. Although November rainfall for Downtown Los Angeles is about 0.6 inch below normal, we usually only get about an inch of rain in November. And don't forget, because of the big storm in October, we are still about 0.6 inch ABOVE normal rainfall for the water year.

Update November 24, 2009. Current equatorial heat content anomalies are about the same as in 2006, not greater. See this composite TAO/TRITON section plot comparing equatorial heat content in 2006 and 2009.

And there are some positive signs. Equatorial Pacific SST and heat content anomalies are much greater than in the short-lived 2006 El Niño, and are more along the lines of those observed in the 2002-2003 El Niño. In addition, a strong MJO has developed. It has remained coherent, and is propagating eastward into the Western Pacific. It already appears to be helping to enhance convection in the Western and Central Pacific, and could kick-start the El Niño engine over the next week or two. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A potent early season Pacific storm carrying the remnants of West Pacific typhoon Melor has hammered California, setting numerous rainfall records, increasing stream flows, and producing heavy snow at the higher elevations of the Sierra.

Several stations, including some in Southern California, recorded precipitation totals exceeding 10 inches. In Santa Barbara County, San Marcos Pass recorded 10.32 inches. In Ventura County Nordoff Ridge recorded 10.04 inches and White Ledge Peak 10.87 inches. Precipitation amounts in Los Angeles County generally ranged from 1 to 3 inches, with orographically favored foothill and mountain locations receiving the higher amounts. Little rain fell in Palmdale and Lancaster because of a pronounced rain shadow effect. Downtown Los Angeles (USC) received 2.03 inches. Here's an archived copy of a NWS Los Angeles/Oxnard Public Information Statement with some rainfall totals for the storm from around the area.

A number of rainfall records for October 13 and 14 fell to the storm, including those for Paso Robles, Santa Maria, Santa Barbara Airport, WFO Oxnard, Burbank Airport, Pierce College in Woodland Hills, LAX, Santa Monica Pier, San Gabriel, and Long Beach Airport. Many of the records broken were set in 1957 and 1968 -- both El Niño years with above average rainfall at Los Angeles.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Los Angeles Temps Continue Below Normal.

Downtown Los Angeles (USC) ended the water year on June 30th having recorded 9.08 inches of rain, which is 6.06 inches below the 1971-2000 norm of 15.14 inches. Some additional water year rainfall totals:

According to the El Nino/Southern Oscillation (ENSO) Diagnostic Discussion issued July 9 by the Climate Prediction Center/NCEP/NWS, "During June 2009, conditions across the equatorial Pacific Ocean transitioned from ENSO-neutral to El Niño conditions." According to the report, El Nino conditions are expected to continue to develop, and last through the NH Winter.

The May-June Multivariate ENSO Index (MEI) value, reported July 6, has increased by 0.51 to +0.85. As was the case last month, the 3-month rise of the MEI (since February-March) is the 4th highest on record for this time of year, and was last exceeded by the strong El Niño of 1997. According to the MEI's originator, Dr. Klaus Wolter, "the combination of already border-line moderate El Niño conditions along with such a big rise in the MEI at this time of year has always been followed by continued El Niño conditions through the remainder of the calendar year, at least in the modern MEI record (since 1950)."

However, as the truncated 2006-07 El Niño event demonstrates, an El Niño is more than just warm Pacific equatorial SSTs. Through complex forcing and feedback mechanisms, the atmosphere and oceans have to cooperate on a global scale. As climate scientist Ed Berry cautions in his July 3rd Atmospheric Insights post, "Should total AAM departures become comparable to that observed during this past January and February, my concerns of an El-Nino 'false alarm' for the weather-climate dynamical system will be significantly raised."

Generally speaking, the momentum of the atmosphere increases when there is an El Niño, and decreases during a La Niña. Over the past 40 days the Global Wind Oscillation (GWO) has retreated from the higher AAM (El Niño) side of the GWO phase space to the lower AAM (La Niña) side. One concern is that two areas of tropical forcing (Indian Ocean and Pacific) may interact in such a way as to quash the El Niño engine. We'll see!

Closer to home, although temps in Southern California have recently been more seasonable, particularly in the Valleys, the last time the average daily temperature in Downtown Los Angeles was above normal was back on May 21 -- 48 days ago.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Instability and moisture associated with a very late season upper level low produced more rain in Southern California Friday, setting a record for June rainfall at Santa Barbara Airport.

Downtown Los Angeles (USC) recorded a total of 0.13 inch of rain Friday. The rainfall increased the water year precipitation total for Los Angeles to 9.08 inches, which is 6.05 inches below normal. Santa Barbara Airport recorded 0.51 inch, setting not only a new record for the date, but for any day in June, as well as for the total amount of rain in June. Here's an archived copy of a NWS Public Information Statement with some preliminary rainfall totals from around the area as of 5:00 p.m. Friday.

The April-May Multivariate ENSO Index (MEI) value (released today) has increased by 0.54 to +0.34. As discussed by MEI originator, Klaus Wolter, the 3-month rise of the MEI since January-February is the 4th highest on record for this time of year, exceeded last by the strong Niño of 1997. According to Dr. Wolter, if next month's MEI rank is at least the same as this month (37th), "it would be unprecedented for it to drop below that high-neutral ENSO-phase range by the end of 2009, virtually excluding a return to La Niña, based on the MEI record since 1950." We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Unusual weather for June. Not so much that there were thunderstorms, but that the thunderstorms were in part the result of an unseasonably strong jet embedded in the base of an offshore upper level low.

It's a bit of a stretch, but an argument could be made that these storms were a calling card of an increasingly energetic atmosphere, and a developing El Niño.

Downtown Los Angeles (USC) recorded a total of 0.02 inch of rain Wednesday. The rainfall increased the water year precipitation total for Los Angeles to 8.95 inches, which is 6.16 inches below normal.

It's not often that a trace of rainfall sets a record, but that was the case at Camarillo Airport and Palmdale, which had not previously recorded precipitation on June 3. The 0.03 inches recorded at Sandberg was also a record. Here's a CNRFC graphic with some 24 hour rainfall totals in Los Angeles County.

Several factors point to an increased probability of El Niño conditions developing over the next few months. Among them, Equatorial Pacific SSTs have increased, and the subsurface heat content is the highest it's been since the El Niño of 2006-07.

But as the short-lived 2006-07 El Niño event demonstrates, an El Niño is more than just warm Pacific equatorial SSTs. Through complex forcing and feedback mechanisms, the atmosphere and oceans have to cooperate on a global scale. Generally speaking the momentum of the atmosphere increases when there is an El Niño, and decreases during a La Nina.

And it looks like the atmospheric momentum may be increasing. Orbits of the Global Wind Oscillation (GWO), a measure of atmospheric momentum, have been shifting upward, in the direction of more energetic values usually associated with an El Niño.

However, an El Niño is not a done deal. The climate system is just leaning in that direction. As climate scientist Klaus Wolter has previously pointed out, in a similar situation in 1973-1975, the climate fell back into a La Niña for another year. But at this point it appears we may be diverging from that analog case. (See June 6 Weathernotes.) We'll see!

Update 06/05/09. Unseasonably strong 110+ kt jet overhead as upper low center moves onshore in Central California. At 7:15 this morning, Intellicast composite radar showed most of the shower activity occurring to the north of Los Angeles, but there has been scattered showers in the Los Angeles area as well, with measurable rain recorded at a number of stations. Here's an archived copy of a NWS Public Information Statement with some preliminary rainfall totals as of 5:00 p.m.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Upper low off the coast of Southern California this morning is forecast to track into Northern Baja by Saturday, and then continue east into Texas Easter Sunday. There's a chance of a shower, or possibly a thunderstorm, over much of Southern California today, diminishing tonight. Tomorrow is expected to be partly cloudy, with mostly sunny skies forecast for Easter Sunday.

Downtown Los Angeles (USC) recorded at total of 0.03 inch of rain Tuesday into Wednesday as a weak front associated with an upper level low moved through the basin. The rainfall increased the water year precipitation total for Los Angeles to 8.93 inches, which is about 5.5 inches below normal. Here is an archived copy of a NWS Public Information Statement, with some precipitation totals from around the area.

A warming trend is expected over the next several days, with high temperatures near 90 by the end of the week.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Compared to last week, GFS and ECMWF runs this week have been much drier in Southern California, with most of the activity focused on the Pacific Northwest. No significant rain is forecast here next week, and both the 6-10 and 8-14 day forecasts project below average precipitation for Southern California.

Recent runs of the GFS show the East Asian jet pumping up a huge, high amplitude ridge in the central Pacific around the dateline, but the resulting downstream trough, jet energy and storm track are forecast to remain above about 40°N.

Model performance has not been the best in recent weeks, and generally suffers during seasonal transitions. However, if the 12z GFS forecast is on the mark, March rainfall for Downtown Los Angeles (USC) would fall well below the 3.14 inch norm. Since normal April rainfall is 0.83 inches, and May only 0.31 inches, beyond March it becomes increasingly unlikely that a big rain event will significantly boost our rainfall total.

Since November 1, Downtown Los Angeles has recorded 8.80 inches of precipitation. This is consistent with the mean November-March precipitation for coastal Southern California during 9 La Niña events from 1948 to the present. (See the composite precipitation map in Weathernotes for October 31, 2008.) The water year total for Los Angeles is now 3.32 inches below normal.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

The precipitation total for Downtown Los Angeles (USC) for February was a little above normal, but not enough to offset January's dry weather. We started out March with a water year rainfall total about 2.4 inches below normal, and as of today we're about 2.73 inches behind.

Tuesday's frontal passages helped a little. Here's a GOES-11 water vapor image from 2:30 in the afternoon, and an Intellicast.com composite radar image from 2:45 p.m. Downtown Los Angeles (USC) recorded 0.25 inch of rain for the storm, and rainfall totals generally ranged from about 0.25 to 0.50 inch. Here is an archived copy of a NWS Public Information Statement listing some rainfall totals.

It looks like our rain season may not be over. Recent runs of the GFS have been hinting at some rain in the 8-10 day timeframe, with a series of systems following. This is consistent with Ed Berry's Atmospheric Insights post today. In response to increased subtropical westerly wind flow, he suggests the possibility of an extended East Asian jet in the week 2-3 timeframe, with possible western USA impacts. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

As forecast by the computer models, most of the precipitation associated with a stream of sub-tropical moisture drawn into California by a large low off the West Coast occurred north of Pt. Conception. Here is an archived copy of a NWS Public Information Statement listing some rainfall totals for the period Saturday night to Monday afternoon. Downtown Los Angeles (USC) recorded only a trace of precipitation.

Both the 6-10 day and 8-14 day NWS Precipitation Outlooks continue to project above normal precipitation in California. At the moment, it looks like the next chance for some rain south of Pt. Conception may be in the Sunday to Monday timeframe, with another opportunity midweek. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Downtown Los Angeles (USC) recorded 1.40 inch of rain in our latest storm, bringing the water year total to 9.37 inches, which is only 0.8 inches below normal for the date. Rainfall totals generally ranged from 1.0 to 2.0 inches in the basin and valleys, with somewhat higher amounts recorded in favored foothill and mountain locations. There was heavy snow in the mountains. Here is an archived copy of a NWS Public Information Statement listing some rain and snowfall totals for the storm.

A large cut-off low pressure complex currently at about 140°W is forecast to spin tauntingly off the coast through Friday or Saturday. Pinwheeling low and vorticity centers, a building ridge, a 150 kt. jet, tropical moisture, and an upstream shortwave are in the forecast mix. At this point it looks like some form of the system moves onshore on Sunday, with most of the rain occurring north of Pt. Conception. However, the situation is extraordinarily complex, and we'll have to see how the forecast evolves.

Beyond next week it looks like there will be additional opportunities for rain in Southern California. Both the 6-10 day and 8-14 day NWS Precipitation Outlooks project above normal precipitation.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Models have been trending somewhat wetter with the front approaching Southern California this morning. BUFKIT analysis of 12z data for Van Nuys generates about 0.4 inch rain, starting around noon and ending this evening. At Santa Barbara the generated total is about 0.5 inch, and at LAX about 0.25 inch. Locally higher amounts are possible in thunderstorms, and on southwest to west facing slopes.

This front is the first of several systems that have been forecast to affect the area over the next week. Model output has been variable regarding the timing and strength of these systems.

According to the models, the system originally forecast for Sunday is still in the works, but has been has been pushed back to Sunday evening or early Monday morning. The !2z NAM and GFS model runs forecast about 1.1 to 1.5 inch at Van Nuys from Sunday evening through Monday. Very strong southerly inflow is forecast with this system, so significantly higher totals are possible on south facing foothill and mountain slopes.

Beyond early next week, the models have been all over the place with some runs forecasting several inches of rain late in the week and other runs almost none at all -- the amount of rain being dependent on the proximity of a strong low to the coast. This morning's GEFS ensembles for next Thursday evening are indicative of the uncertainty. We'll see how the forecast evolves over the next few days.

Update 02/18/09. Here is an archived copy of a NWS Public Information Statement with some rainfall totals for Friday's storm.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

The first of a series of upper lows, troughs and shortwaves expected to affect Southern California over the next several days has resulted in widespread rain, with storm totals in excess of 1.0 inch in many areas. Yesterday, new rainfall records were set for the date at Burbank and Lancaster. Many stations have recorded more rain in the past twelve hours than in the entire month of January.

Another Pacific system is working down the coast and is expected to result in periods of rain today, tonight and into Saturday. A break in the action is forecast on Sunday, but some showers are a possibility.

In a situation that has become too familiar this rain season, Sunday evening a trough is forecast to dig down the backside of a ridge along the West Coast. Model forecasts have varied from run to run, but the trough is expected to produce some rain in our area Sunday evening into Monday. A more westward track, over the Pacific, would likely produce more rain, and a more eastward track less.

This generally wetter pattern may continue into the 8-14 day period. The active phase of the Madden-Julian Oscillation (MJO) and the Global Wind Oscillation (GWO) are supporting a general circulation pattern that is favorable to West Coast troughs. In addition, a major Sudden Stratospheric Warming (SSW) event is underway and associated high latitude blocking might eventually result in a southward shift of the storm track over the U.S.

Both the 6-10 day and 8-14 day precipitation outlook from the CPC are indicate the possibility of above average rainfall in Southern California. We'll see!

Update 02/10/09. Here are the updated and corrected storm totals from the NWS for the period 4:00 a.m. Thursday to 4:00 a.m. Sunday. It looks like Wednesday's system should fall apart south of Pt. Conception, but if recent model runs hold true, Southern California is in store for more wet weather. Relatively weak shortwaves are forecast for Friday and Saturday, but these set the stage for more potent systems Sunday and mid-week. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Weather is by nature chaotic, and not perfectly predictable. From a given starting point, small variations in initial temperature, pressure, moisture, and other factors in the weather system can lead to dramatically different outcomes. In addition, interactions of earth's oceans and terrain with the atmosphere further complicate predictability.

Two periods of rain were recently forecast in Southern California -- one from Wednesday into Saturday, and another from Sunday evening into Tuesday. Model projections varied from day to day and run to run. At one time it looked like the Los Angeles area might get about an inch or rain out of both systems. So what happened?

Considering the first period, Wednesday into Saturday, here are the preliminary rainfall totals from the NWS. Note how much the rainfall varies. In the Los Angeles basin, Downtown Los Angeles (USC) recorded 0.34 inch, LAX recorded 0.51 inch and Santa Monica recorded 0.76 inch. Locations that benefited from orographic enhancement recorded higher totals. For example. Pacioma Dam recorded 1.11 inch, Warm Springs 1.31 inch, and OPIDS Camp 1.54 inch. Some stations in Santa Barbara and San Luis Opisbo counties received as much as 2-3 inches of rain. A slight change in the position of low to the south on Wednesday and Thursday, or the low to the west on Friday and Saturday could have easily resulted in much more rain.

We're in the middle of the second period now. Instead of an over the ocean path forecast a couple of days ago, the cold trough and upper low that is over the southwest took a drier overland course down the West Coast. Nonetheless, there has been scattered showers in Southern California, and even isolated thunderstorms, lightning and hail. It's not a huge step to speculate the rainfall would have been more widespread if the system had taken a more westward path, and picked up additional moisture.

So what's next? Globally, some interesting things are occurring that could impact our weather over the next few weeks. The MJO and GWO are expected to continue their circuit into phase 3-4. This might open the door to more West Coast troughs, or MJO enhanced rainfall. A Sudden Stratospheric Warming (SSW) event appears to be underway and may result in polar air outbreaks that would affect the mid-latitude circulation.

However, in the short term Los Angeles rainfall remains below normal. As of January 25, Downtown Los Angeles (USC) has recorded 5.00 inches of rain this water year, which is 1.38 inches below normal. Last year, the water year total on January 25 was 9.35 inches. The ECMWF and GEFS ensembles suggest the possibility of a strong trough affecting California around February 4th or 5th, but that is a long way out, and we'll have to see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Including today, Los Angeles has enjoyed an unprecedented ten straight January days with highs in the eighties. In the yin yang of weather, the western half of the U.S. has been enjoying unusually warm temps, while the eastern half of the country has shivered.

Since the start of the water year on July 1, Downtown Los Angeles (USC) has recorded 4.66 inches of rain. Just 10 days ago, 4.66 inches was almost exactly normal rainfall for the date. However, as is so often the case in Southern California, this apparent normality was the sum of offsetting wet and dry periods. December's precipitation was generally well above normal, but January has been dry, dry, dry. Today, the Los Angeles rainfall total is about 1.10 inch below normal, and every day it doesn't rain, our deficit increases by about 0.10 inch.

Our warm temperatures and dry weather have been the result of a high amplitude ridge, pushed up over the West Coast by a very strong and extended Pacific jet stream. Big upper level ridges such as this are consistent with La Nina, and have been a recurring theme this Fall and Winter. Much of our rainfall and cold weather this season has occurred when an extended Pacific jet collapses or contracts -- as is occurring now -- and the blocking ridge shifts westward, opening the door to cold storms plunging down the backside of the ridge from the north.

This time there is a wildcard in the mix. One of the reasons the Pacific jet has been extended is the active phase of the Madden-Julian Oscillation (MJO) has recently propagated from west to east, across the Pacific. The system that is forecast to affect Southern California Wednesday night into Thursday looks like it might be enhanced by an inflow of moisture from an area of tropical convection that may be associated with the MJO.

How much might it rain? A BUFKIT analysis of 12z NAM data generates 1.3 inches of rain at Van Nuys for the period Wednesday evening through Thursday afternoon. The HPC 2 Day forecast is not so bullish, indicating about 0.50 inch to 0.75 inch over the area. We'll see!

Medium range models suggest the weather in the West could remain unsettled into next week and beyond. Of particular interest is this morning's 12z ECMWF forecast for mid-week next week, which projects the retrogression of the West Coast ridge to 150-160°W, with a cold, wet pattern similar to what we saw in December. That would be quite a change!

Update 01/22/09. It seems the NAM and GFS models can't get a handle on the system currently affecting our area. The 12z NAM generates 1.6 inches (!) of rain at Van Nuys and the 12z GFS 1.2 inches at LAX from this morning into Saturday afternoon. On the other hand the 09z SREF Ensembles puts the probability of more than 0.25 inch of rain for the 24 hr. period ending mid-morning Friday at about 50%, and then only about 10-30% for the following 24 hr. period. Upslope enhancement may produce higher totals on south facing foothill and mountain slopes. The GFS continues to advertise the possibility of a significant rain event Monday afternoon into Tuesday or Wednesday, but given recent model performance, we'll wait and see!

Update 01/21/09. The 12z models now extend the rainy period for the first system into Saturday. The 12z NAM generates about 1.0 inch of rain at Van Nuys, beginning Thursday morning and ending Saturday midday. The 12z GFS also produces about 1.0 inch, beginning Wednesday evening and ending Saturday afternoon. The GFS adds another 0.9 inch from Sunday morning to Monday night. Somewhat higher amounts would be expected in some foothill and mountain locations. As always, we'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A Pacific storm system -- which at one point was expected to be the wettest of the rain season thus far -- took a more westward track and skirted the coast of Southern California on Christmas Eve, generally producing only modest rainfall across the area.

Today, the trough digging down the coast is further west that forecast. (In retrospect this might have been foreseen taking into account the GWO phase 1-2 transition.) In any case, the flow into California has been moist and cyclonic, and rain has continued in many areas, with snow at the higher elevations.

A front associated with this trough is working its way down the coast, and early this afternoon is just north of Los Angeles. This could add a little more to our rainfall totals as it moves through later today. We'll see!

Update 12/26/08 10:30 am. Here are some preliminary storm totals from the NWS Los Angeles/Oxnard and storm totals from the NWS San Diego.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A potent appearing Pacific storm system is developing off the coast of Oregon and Northern California and headed our way. Significant rain, with snow at the higher elevations, is expected over much of the state.

Rain associated with this system is forecast to begin in Northern California this evening. At the moment, it looks like prefrontal rain could develop in the Los Angeles area tomorrow morning. Rainfall rates are forecast to increase Christmas Eve, and then taper off during the day on Christmas.

Although the models appear to be converging on similar solutions, there has been a lot of variability from run to run. This is due in part to the difficulty of the forecast. The intensity of the low, the path of the low center, the amount of moisture available to the system, the upper and lower level jet dynamics and other factors could change the amount of rainfall.

The HPC QPF forecast for the period Tuesday afternoon to Friday afternoon shows about 1.25 to 1.50 inches along the coast with up to about 3 inches in the mountains. These amounts could be somewhat understated. We'll see!

The system that moved through the Los Angeles area Sunday night into Monday was a little stronger than expected, with rainfall amounts generally ranging from about 0.1 inch to 0.25 inch. Here are some preliminary rainfall totals from the NWS.

Update 12/24/08 11:00 am. 12z NAM and GFS forecast a more westward track of the low and have backed off precipitation amounts forecast for the Los Angeles area. The 12z NAM generates about 0.6 inch at Van Nuys and the 12z GFS only about 0.26 inch for the storm. HPC's latest 2-day Quantitative Precipitation Forecast indicates precipitation amounts ranging from about 0.75 inch to 1.50 inch in coastal Southern California. On the other hand, the 06z high resolution WRF-NMM was quite wet, with precipitation amounts in our area ranging from 1.0 to 4.0 inches.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A cold upper level low produced widespread rain and snow in Southern California, closing highways, fouling traffic, and chilling Southlanders. As much as a foot of snow was reported in the Antelope Valley and the snow level dropped to near 2000 ft in the foothills and mountains of Ventura and Los Angeles counties.

As forecast by the NAM/WRF, the precipitation totals were higher to the south of the Los Angeles basin. This Intellicast.com animated loop shows the pattern of rain and snowfall from Tuesday evening to Wednesday evening. Here are some preliminary storm totals from the NWS Los Angeles/Oxnard and storm totals from the NWS San Diego.

Downtown Los Angeles (USC) recorded 0.51 inch for the storm, bringing the water year rainfall total at Los Angeles to 2.79 inches. As of December 17, this is 1.41 inches above normal, and 0.34 inch more rain than we had last year on this date.

What's next? RAMDIS 4km water vapor animation shows a weak disturbance northwest of Pt. Conception, moving east toward the Central Coast. Although today's 18z NAM/WRF is dry overnight south of about Monterey, this area of vorticity could produce a shower north of Pt. Conception. After that, things should stay dry in Southern California until around Monday, when a fast moving front sweeps through the state. Later in the week, sometime around Christmas, the models are suggesting the possibility of a major system impacting California. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

An intense upper level low, fed in part by moisture that originated in the subtropical mid-Pacific, produced widespread rain in Southern California, with snow at the higher elevations. Precipitation totals generally ranged from about 1 to 3 inches, and new rainfall records for December 15 were set at LAX, UCLA, Long Beach, San Gabriel and Santa Barbara. Here are some preliminary rainfall totals from the NWS.

A very cold core upper level cutoff low is currently spinning off the California coast. A GOES sounding from this afternoon indicated a temperature of -33°C at the 500 mb level and significant instability. The low is forecast to move onshore over the next 24 hours, and slight changes in its trajectory could have a big impact on precipitation amounts and intensity.

The NAM/WRF has been quite a bit drier in the Los Angeles area than the GFS, with the heaviest precipitation occurring south of the basin. The latest (00z) run of the NAM appears to be wetter in the Los Angeles area than runs earlier today. With such cold temperatures aloft, heavy rain and strong thunderstorms are a possibility, particularly wherever the low moves onshore. BUFKIT analysis of PMD and VNY data suggests the snow level could drop to 2000-2500 ft., perhaps lower in heavy showers. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Happy Thanksgiving! Our record-setting upper low system is slowly moving east out of the area, but this morning there's still some shower activity occurring south and east of the Los Angeles basin. The best chance of showers today is in the mountains, and areas south and east of the basin, but a shower could pop up just about anywhere in Southern California.

Rainfall totals for the storm have generally ranged from 1.0 to 2.0 inches in the coastal and valley areas, with some higher amounts recorded in foothill and mountain locations. Rainfall records for November 26th were broken at several locations, including Lancaster, Palmdale, Sandberg, UCLA, Burbank, Woodland Hills, and San Gabriel. OPIDS Camp, in the San Gabriel Mountains has recorded 3.29 inches. Here are some preliminary rainfall totals from the NWS.

Through yesterday, Downtown Los Angeles (USC) has recorded a storm total of 1.60 inches, bringing the water year total to 1.87 inches, which is 0.17 inches above normal for the date.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Downtown Los Angeles (USC) happened to be under the right cloud yesterday, and recorded 0.02 inch of rain. There's a continuing chance of showers in Southern California through the weekend. The area could use some rain. The last storm to produce more than a couple tenths of inch of rain at Downtown Los Angeles was back on February 24, 2008 -- more than eight months ago.

Last year, California's rain season might have been scripted by Dr. Jekyll and Mr. Hyde. Lowland rain totals and the Sierra snowpack were well above normal through the end of February, and then the spigot was turned off. The storm track shifted north, and California had its driest March to May on record. (The March 29, 2008 post in Ed Berry's Atmospheric Insights blog describes the events that may have led to and maintained this shift.)

Which rain season personality will emerge this Winter? Earlier this year the equatorial Pacific tried to transition to El Nino, but the atmosphere didn't cooperate. As measured by the Multivariate ENSO Index (MEI), the ENSO state has returned to the weak La Nina threshold. And as measured by the Global Wind Oscillation (GWO), an uncooperative atmosphere has continued to cycle through a La Nina base state.

This suggests a winter precipitation outlook with a La Nina flavor -- similar to last year. This precipitation map, generated by the ESRL-PSD Composite ENSO plots page, shows the mean November-March precipitation for the U.S. during 9 La Niña events from 1948 to the present. The average La Niña rainfall indicated for coastal Southern California is in the 7.0-10.5 inch range. Last season's November-March rainfall in Downtown Los Angeles was about 12 inches.

Here's the current Nov-Dec-Jan precipitation outlook issued October 16 by the Climate Prediction Center. The "EC" means an equal chance of below normal, near normal, or above normal precipitation. The IRI Multi Model Seasonal Forecast for Nov-Dec-Jan is similar. We'll see!

Update 11/4/08. Here are the NWS Public Information Statements with preliminary rainfall totals for the period from Friday evening to Sunday morning, and from overnight last night to 10:00 a.m. this morning. The current Climate Prediction Center 6-10 day and 8-14 Precipitation Outlooks project below normal rainfall for Southern California. In Atmospheric Insights, Ed Berry paints a scenario with an extended North Pacific Jet collapsing into a strong western U.S. trough in the week 2-3 timeframe. We'll see!

Update 11/1/08. Did a trail run this morning in the Pt. Mugu State Park Area. Over the course of 3+ hours watched 2-3 waves of convection march northeast from the Santa Barbara Channel across the Oxnard Plain. We were showered on a few times, but were very happy to be east of these training T-storms and heavy rain. Here is a NWS Public Information Statement with some rainfall totals as of 11:00 a.m.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Downtown Los Angeles recorded a trace of rain, and a few other stations in Southern California recorded meager, but measurable, precipitation Monday. Where it did rain, amounts of a few hundredths of an inch or less were the norm. A good cell must have developed over the southwestern San Gabriel Mountains -- a NWS technical discussion mentioned that 0.5 inch was recorded at Big Tujunga Dam.

Following our "welcome to Summer" heatwave back in June, summertime temperatures have generally been seasonable. Yesterday, Los Angeles Pierce College recorded a high of 102°F, and inland temperatures today appear to be running a little warmer.

This weekend temperatures are expected to drop dramatically as a Pacific storm system and it's unseasonably strong 165+ kt jet affect the west coast this Friday into Saturday. If this morning's 12z GFS verifies, as much as 3-4 inches of precipitation could occur in the mountains of Northern California, Oregon and Washington. At high elevation some of this precip could be in the form of snow.

The front associated with the trough is currently forecast to hold together south of Pt. Conception and could produce some showers in the Los Angeles area on Saturday, particularly in the mountains. A BUFKIT analysis of 12z GFS data generates about 0.3 inch of rain at Van Nuys, but given the time of year, and the ample time remaining between now and Saturday, we'll have to see!

Ed Berry first mentioned the possibility of an "anomalous extended North Pacific Ocean jet collapsing into a western USA trough" in a September 6, 2008 post on Atmospheric Insights, and refined the projection, including a timeframe, in subsequent posts.

Update 10/06/08. Saturday's trough and front behaved about as expected with scattered light rainfall around the area. Precipitation amounts generally ranged from a trace or less to about 0.1 inch or so in some foothill and mountain locations.

Update 10/03/08. Focus of the incoming storm system continues to be Northern California and the Pacific Northwest. A BUFKIT analysis of 12z NAM data shows the expected north to south gradient in projected precipitation. About 0.5 inch is projected at Monterey, 0.2 inch at San Luis Obisbo, 0.1 inch at Santa Barbara, and 0.06 inch at Van Nuys. The 09z SREF Ensembles suggest a high probability, low precipitation event in the Los Angeles area with about a 90% probability of more than 0.01 inch of rain, but less than a 10% probability of more than 0.1 inch. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

More Wet Weather Possible Today and Tomorrow.

The unseasonably energetic upper level low that replaced our unseasonably strong high has resulted in dramatic weather in Southern California, including heavy rain, hail, thunderstorms, lightning, and even a pair of tornadoes near March Air Force base. This UCAR regional radar image from yesterday at 5:00 p.m. shows the intense cell that likely spawned the tornadoes.

In Los Angeles County, very heavy rain was recorded in the San Gabriel Valley. According to a NWS Public Information Statement, as of 7:00 p.m. yesterday, 2.29" was recorded at Santa Fe Dam, 1.51" at Whitter Narrows, and 1.42" at the San Gabriel River at Valley. Yesterday, Downtown Los Angeles (USC) recorded 0.05 inch of rain, bringing the water year total to 13.47 inches.

Intellicast radar shows showers continuing in Southern California this morning. The upper level low is forecast to remain over Southern California into Sunday, and BUFKIT analysis of 12z NAM data for several Southern California stations (VNY, LAX, ONT) suggest on and off rain showers may occur through Sunday morning. As long as the cut-off upper low remains over the area there is also the possibility of an isolated heavy shower or thunderstorm developing. We'll see!

Update Sunday, May 26, 2008. Here is an archived copy of a NWS Public Information Statement with rainfall totals for this event through 6:00 p.m. Saturday.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

In it's April 30 ENSO Wrap-Up, the Australian Bureau of Meteorology characterizes Pacific climate patterns as being generally neutral, "with the majority of indicators returning to near-normal levels." The April 28 ENSO Update from the CPC suggests that La Niña will continue through May-July 2008, but many of the factors discussed indicate general weakening of the cold ENSO episode.

We've had only a smattering of rain at Downtown Los Angeles since 0.46 inch was recorded back on February 24. A miniscule 0.01 inch was recorded on March 15, and 0.04 inch on April 2. These NOAA/NWS AHPS Precipitation Analyses map the 60 day Departure from Normal Precipitation and 60 day Percent of Normal Precipitation for the southwestern U.S., as of April 30, 2008.

As of May 1, the water year rainfall total for Downtown Los Angeles (USC) stands at 13.42 inches. This is 90% of the 1921-2006 average of 14.87 inches. According to the 1921-2006 dataset, the average amount of precipitation in May and June has been 0.3 inch and 0.1 inch, respectively. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Normal precipitation. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

A weak cold front held together a little better than expected, producing a few showers in the Los Angeles area early Sunday morning. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 5:00 p.m. No measurable rain was recorded at Downtown Los Angeles (USC- KCQT).

Only 0.01 inch of rain was recorded at Downtown Los Angeles (USC- KCQT) the entire month of March, pulling the water year rainfall total more than a 0.5 inch below normal for the first time this rain season. It looks like there's a pretty good chance of some rain Wednesday. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Weather conditions were tough for the Amgen Tour of California cyclists cranking over Mill Creek Summit yesterday. The Mill Creek RAWS recorded an average temperature of 35°F, with winds of 25 mph, gusting to 40 mph, at about the time the peloton cleared the summit. The Clear Creek RAWS, where riders turned right onto Angeles Crest Highway, recorded about 0.20 inch of rain during the afternoon, with the temperature hovering at around 40°F.

As bad as it was for the tour cyclists, the system was generally not as wet as expected -- particularly in the Los Angeles County mountains, where precipitation amounts ranged from about 0.25 inch to about 1.0 inch. Similar rainfall amounts were recorded in the Los Angeles basin and valleys.

Downtown Los Angeles (USC- KCQT) recorded 0.07 inches of rain Saturday, and 0.46 inches Sunday, bringing the water year total (since July 1) to 13.37 inches, which is about 3.1 inches above normal for the water year to date.

Since mid-week last week some Sierra snow sensors have recorded as much as 8 or 9 inches snow water equivalent of precipitation -- the rough equivalent of 6 or 7 feet of snow. Today's Statewide Summary of Snow Water Equivalents, provided by the California Cooperative Snow Surveys, reports the Sierra snowpack at 119% of normal for the date and 101% of the average April 1 seasonal total.

It looks like most of the west coast weather action will be shifting to the Pacific Northwest for the next week or so. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Rapidly intensifying Pacific low pressure system approaching the west coast looks very impressive on satellite images this afternoon, with strong upper and low level jet dynamics, a good moisture feed, and a classic baroclinic leaf.

The system is forecast to be filling as it moves onshore, but a very strong jet max moving through the base of the trough should keep the dynamics interesting. In any case, significant rain is expected throughout much of California over the weekend, with heavy snow in the Sierra.

Southern California is forecast to be on the southern margin of the action, however in keeping with the wet trend this rain season, the 18z GFS is forecasting about 1.5 inches of rain at Los Angeles from midday Saturday through Sunday afternoon, and the 18z NAM about 1.0 inch. A moderately strong mid-level southerly to southwesterly inflow should increase precipitation amounts in favored foothills and mountain locations.

Precipitation totals resulting from the passage of the second trough yesterday afternoon into this morning have ranged from about 0.25 to 0.75 inch in the Los Angeles area, with up to about 1.0 inch recorded at some locations. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. Isolated showers have continued to pop up around the Los Angeles area much of the day, but are forecast to be ending in most areas this evening.

Downtown Los Angeles (USC- KCQT) recorded 0.19 inches of rain Thursday, bringing the water year total (since July 1) to 12.84 inches. We're still at a deficit for the month of February, but remain above normal for the water year to date. Much of the February deficit may be erased by Monday. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Precipitation totals from the first of a series of shortwaves associated with a extended Pacific jetstream produced rainfall amounts ranging from about 0.1 to 0.25 inch in the Los Angeles area yesterday, with up to about 0.5 inch recorded in some mountain locations.

Downtown Los Angeles (USC- KCQT) recorded 0.14 inches of rain Wednesday, bringing the water year total (since July 1) to 12.27 inches -- still about 2.5 inches above normal for the date. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. yesterday afternoon.

There were a few sprinkles this morning, and Intellicast composite radar shows some shower activity around the area at 12:30 p.m. this afternoon. More general rain is expected to develop this afternoon or evening. Today's 12z NAM projects about 0.6 inch at Los Angeles between now and mid-morning Friday. Over that same period, a BUFKIT analysis of 12z NAM data for Van Nuys projects about 0.75 inch, but an analysis of 12z GFS data generates only about 0.25 inch.

A third system is forecast for the Saturday afternoon into Sunday timeframe and is expected to produce similar amounts of precipitation. However, the upper level flow will be transitioning to a more amplified pattern, so the computer models may have some difficulty with the forecast. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Below Normal precipitation.

More information concerning Southern California weather can be found using our WEATHER LINKS page.