# Tuesday, March 20, 2012

GOES-15 Water Vapor Image from Saturday, March 17, 2012 at 12:00 pm PDT Click
GOES-15 Water Vapor Image
Saturday, March 17, 2012 at 12:00 pm PDT

Updated 03/29/12. Edited to include the rainfall total from October 5 in the Downtown Los Angeles rainfall comparison.

Although there were scattered showers throughout much of Southern California Sunday morning, the Los Angeles Marathon beat the 70/30 odds for measurable rain and stayed dry. Given the cool and breezy conditions, I'm sure runners were glad the precipitation forecast worked out on the dry side!

According to KCQT data Downtown Los Angeles (USC)recorded 0.76 inch for the storm, bringing the water year total to 5.98 inches, which is 46% of normal for the date. This was less than the 1.15 inch recorded Downtown on October 5, the 0.90 inch recorded on November 20, and the 0.96 inch recorded December 12-13, but in some areas Saturday's storm was wetter than any of these storms.

Because of the very strong southwesterly inflow that accompanied the storm, upslope precipitation enhancement produced some impressive totals in the foothills and mountains. For example, West Fork Heliport recorded 3.82 inches, OPIDS Camp 4.49 inches, Mt. Baldy 3.76 inches, and Nordhoff Ridge 5.32 inches. Here are some preliminary rainfall totals from around the area compiled by the NWS, and a snapshot of a Ventura County Watershed Protection District Google Map (PDF) with some additional rainfall totals.

Here are a NEXRAD regional radar image, water vapor satellite image, IR satellite image and RAMDIS visible satellite image of the system at noon Saturday. The parent low north of Pt. Conception is beautifully structured and there is strong convection associated with the frontal boundary south of the Los Angeles.

On a run in the Santa Monica Mountains Sunday morning, I found melting graupel in the Santa Monica Mountains at an elevation of about 2300' along Castro Mtwy about a mile east of Castro Peak. This cell that appears to be the best candidate for the producing the graupel is shown in this KVTX NEXRAD radar image from about 9:00 am PDT Saturday morning.

Both the GFS and ECMWF medium range models show a trough evolving into an upper level low just off the Central California coast this weekend. It's too early to put much credence in the forecast, but some precipitation in the Saturday to Monday timeframe looks like a possibility. We'll see!

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Tuesday, March 20, 2012 8:55:59 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, March 16, 2012

WRF Ensemble Precipitation Forecast from 03/16/12 12z Click
BUFKIT Display of WRF Precipitation Forecast
03/16/12 12z

Updated 03/29/12. Edited to correct the date for the most rainfall in a day this season (through March 16) at Los Angeles.

It's been a bleak rain season. So far the most rainfall Los Angeles has recorded in a day this season was in the record-setting early season storm October 5, when Downtown recorded 1.15 inch of rain. As of today Los Angeles' water year rainfall total stands at a meager 41% of normal.

If current forecasts verify, the rainfall total at Los Angeles for this weekend's storm might exceed last October's storm. Maybe. BUFKIT display of WRF ensemble precipitation forecast shows a spread from 0.4 inch to about 1.1 inch at LAX, and from about 0.65 inch to 1.6 inch at Van Nuys. The 18z WRF/NAM run was wetter than the 12z run producing about 0.95 inch at LAX and 1.1 inch at Van Nuys. A strong southwesterly inflow of around 35-40 kts is forecast and could produce higher precipitation amounts on foothill and mountain slopes which have a southerly to westerly aspect.

The Los Angeles Marathon is this Sunday, and after last year's record-setting Marathon day rainfall, many are wondering about the weather on Sunday. Last year of 19,798 runners that completed the race, more than 10,000 were on the course for longer than 5 hours and nearly 2000 were out there for longer than 7 hours. The Elite Men and most of the runners start at 7:24 am, so the majority of runners will finish after noon.

Check with the NWS for the latest official information, but as it looks now the bulk of the rain is forecast to occur on Saturday and the Marathon will be run after the cold front has passed through the area. This is a different weather scenario than last year, but one that can produce cold, showery, blustery conditions with strong winds out of the northwest. In the unstable conditions that typically follow a cold front heavy showers, gusty winds and even a thunderstorm are possible. The HPC 6-Hour Probabilistic Precipitation Guidance for the periods ending 10:00 am Sunday morning and 4:00 pm Sunday afternoon indicate a high probability of at least 0.01 inch of rain in the Los Angeles area. We'll see!

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Friday, March 16, 2012 2:15:36 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, February 26, 2012

ESRL/PSD Analog 8-14 Day Probabilistic Precipitation Forecast Click
ESRL/PSD Analog 8-14 Day Probabilistic Precipitation Forecast
Probability of more than 25mm precipitation from 03/04/12 to 03/10/12.

Wednesday Downtown Los Angeles' water year rainfall total fell below 50% of normal for the date. With only 5.22 inches of rain in the bucket it looks like we're headed toward the driest rain season since the record-setting dry water year of 2006-2007, when a meager 3.21 inches was recorded. If Los Angeles ends the rain year (June 30) with less than 7.16 inches of precipitation, the 2011-2012 water year would be one of the ten driest on record.

It's been dry throughout most of Southern California and much of the state. According to data compiled by the NWS Burbank's water year total now stands at a paltry 34% of normal; Long Beach 49% of normal; Camarillo 42% of normal; Santa Barbara 56% of normal; and Paso Robles 49% of normal. Southernmost California has fared a little better with San Diego at about 79% of normal for the date. Central California rainfall is also well below average with San Francisco at 35% of the normal, San Jose at 26% and Sacramento at 40%.

I received an email recently from a reader asking if I thought a March Miracle was likely this year. Keeping in mind the chaotic nature of weather, and that low probability events do sometimes occur, the short answer is that I don't think it's likely we'll see higher than normal rainfall this March.

In a post in early October I discussed what the impact of a second year La Nina might be on 2011-12 Winter precipitation in the continental U.S. For a selection of seven second year La Ninas the coastal Southern California climate division recorded about 5 to 6 inches less precipitation than normal for the period November through March. If we take a look at March rainfall in that same selection of second year La Ninas, four of the seven recorded less than 0.5 inch rain in March, and only one was well above average -- 4.83 inches in March 1975.

Current outlooks are not favorable for higher than average March precipitation. The Climate Prediction Centers 6-10 Day Precipitation Outlook, 8-14 Day Precipitation Outlook, and One Month Precipitation Outlook all indicate below normal precipitation in Southern California. The ESRL/PSD Analog Probabilistic Precipitation Forecast is also dry in the 6-10 and 8-14 day outlook period, and the PSD Ensemble Spread does not look encouraging.

On the climate side of things the active phase of the MJO has been stalled in the Indian Ocean, but the 15-day ensemble ECMWF and several models forecast increased amplitude and eastward propagation. As a result of strong negative East Asian and Tropical torque events, relative atmospheric angular momentum is dropping like a rock, with the GWO taking a big dive into La Nina territory. Should the MJO continue to propagate and AAM increase over the next 2 weeks, perhaps we'll see the scenario necessary to generate an extended Pacific jet strong enough to impact the West Coast.

Monday its looking like we may get a little rain and possibly some lower elevation snow. Goes soundings and model data indicate the Pacific system is moisture-starved, but it is quite cold and is forecast to have strong dynamics. A GOES sounding near the systems core showed a 500mb temp of -30°C. Precipitable water values in the circulation around the low were around 0.6 inch. With such cold air aloft, and strong system dynamics, strong convection is a possibility. We'll see!

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Sunday, February 26, 2012 3:37:30 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, January 20, 2012

HPC 5-Day Precipitation Forecast Issued Friday Afternoon, January 20, 2012 Click
HPC 5-Day Precipitation Forecast
Issued Friday Afternoon, January 20, 2012

Last Sunday's upper level low resulted in a little rain, mostly south of the L.A. basin, but Southern California and much of the West has been dry, dry, dry. How dry? Take a look at this plot of percent of average precipitation for the past 90 days from the Western Regional Climate Center.

Downtown Los Angeles (USC) has not recorded measurable rain for more than a month. The last measurable rain was on December 17 when 0.01 inch recorded. The water year precipitation total for Los Angeles has been stuck on 3.76 inches, which is about 2.5 inches below normal. The Sierra has been especially dry. The Statewide Summary of Snow Water Content for January 18 reported the snowpack at 10% of normal. Remarkably, Mammoth Mountain recorded no natural snow between December 5 and January 19!

The good news is the very stubborn West Coast ridge has finally relented, opening the door to a more zonal flow and a sequence of shortwave troughs. The change in pattern is forecast to produce significant rain and snow over most of the West Coast the next few days. The HPC 5-day Precipitation Forecast indicates up to about 5 inches of precipitation in some areas of the Sierra and North Coast, and over 9 inches in some areas of the Pacific Northwest.

The change in pattern isn't forecast to produce much rain south of Pt. Conception, but at this point just about any amount would be helpful. BUFKIT analysis of WRF Ensemble forecasts for Van Nuys indicate precipitation amounts ranging from about 0.1 inch to 0.5 inch, beginning sometime this evening and ending midday Saturday. The 18z NAM precipitation forecast for Van Nuys projects about 0.25 inch for the storm. Some mountain areas could see somewhat higher precipitation totals, particularly those with a west-facing aspect.

Another shortwave is forecast to move through the area Monday. Model projections differ, but we could get a little rain out of that system as well. We'll see!

Update January 25, 2012 8:00 am PST. Precipitation totals across the area from Monday's system generally ranged from about 0.3 inch to 0.75 inch. Downtown Los Angeles (USC) recorded 0.62 inches for the storm. This combined with the 0.68 inches from Saturday's system boosted the water year total for Los Angles to 5.06 inches, which is about 75% of normal for the date. The medium range models have been all over the place. Yesterday the 12z GFS forecast for Monday morning depicted an upper low and trough on the West Coast, while the ECMWF indicated some ridging. Here's a GFS/ECMWF comparison from San Jose State University Meteorology. Given the recent Sudden Stratospheric Warming (SSW) and rejuvenation of the MJO there's plenty of uncertainty in the medium range. The ECMWF seems to like the idea of a relatively fast-moving trough affecting the West Coast sometime around February 1. We'll see!

Update January 21, 2012 1:30 pm PST. Perhaps because its jet stream dynamics were more favorable than expected, this first system was a little stronger and held together a little better south of Pt. Conception than suggested by the models. Rainfall totals tabulated by the NWS generally ranged from about 0.2 to 0.7 inch in the Los Angeles area, with somewhat higher totals recorded in Ventura County and Santa Barbara County. Model projections have varied on the strength of the system forecast to move through the area on Monday. The 12z NAM projected about 0.4 inch for Van Nuys; the 18z NAM about 0.3 inch, and the 12z GFS about 0.5 inch. The system appears similar to today's, but it looks like the shortwave trough and vortex max may track more directly into Southern California.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Friday, January 20, 2012 3:33:43 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, January 03, 2012

Following is a chart comparing the 2011-12 La Nina to other cold ENSO episodes that have occurred since 1949. With the exception of 1961-62 and 2008-09 the cold episodes are based on the Oceanic Niño Index (ONI) and are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. A description of the parameters follows the chart. A GWO phase space plot is included for those cold episodes for which AAM data is available. Data for 2011-12 will be updated periodically.

Year Nov-Mar
AAM
Peak MEI4 Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1949-501,2 -- -1.423 APRMAY -1.7 DJF 9.94 --
1950-511 -- -1.247 NOVDEC -1.0 NDJ, DJF 8.21 --
1954-551 -- -1.578 MAYJUN (54) -1.2 ASO 11.94 --
1955-561 -- -2.276 MAYJUN (55) -2.0 OND 16.00 --
1956-571 -- -1.516 MAYJUN (56) -0.9 SON, OND 9.54 --
1961-623 -0.513 -1.093 DECJAN -0.6 ASO, SON 18.79 Click for Nov-Mar GWO Phase Space Plot
1962-63 -1.259 -0.843 JANFEB -0.7 OND, NDJ 8.38 Click for Nov-Mar GWO Phase Space Plot
1964-65 -1.145 -1.496 JULAUG -1.2 SON, OND 13.69 Click for Nov-Mar GWO Phase Space Plot
1967-68 -0.770 -1.060 APRMAY -0.9 JFM 16.58 Click for Nov-Mar GWO Phase Space Plot
1970-71 -0.976 -1.898 MARAPR -1.3 DJF, JFM 12.32 Click for Nov-Mar GWO Phase Space Plot
1971-72 -0.173 -1.463 AUGSEP -1.0 OND 7.17 Click for Nov-Mar GWO Phase Space Plot
1973-74 -1.331 -1.942 DECJAN -2.1 NDJ 14.92 Click for Nov-Mar GWO Phase Space Plot
1974-75 -0.842 -1.255 OCTNOV -0.9 OND 14.35 Click for Nov-Mar GWO Phase Space Plot
1975-76 -0.713 -2.000 SEPOCT -1.7 OND, NDJ 7.22 Click for Nov-Mar GWO Phase Space Plot
1984-85 -0.597 -0.743 APRMAY -1.1 NDJ 12.82 Click for Nov-Mar GWO Phase Space Plot
1988-89 -1.139 -1.591 AUGSEP -1.9 OND, NDJ 8.08 Click for Nov-Mar GWO Phase Space Plot
1995-96 -0.227 -0.644 DECJAN -0.7 OND to JFM 12.46 Click for Nov-Mar GWO Phase Space Plot
1998-99 -0.541 -1.233 JANFEB -1.4 NDJ, DJF 9.09 Click for Nov-Mar GWO Phase Space Plot
1999-00 -0.781 -1.242 JANFEB -1.6 NDJ, DJF 11.57 Click for Nov-Mar GWO Phase Space Plot
2000-01 -0.795 -.755 OCTNOV -0.7 NDJ 17.94 Click for Nov-Mar GWO Phase Space Plot
2007-08 -1.010 -1.631 FEBMAR -1.4 DJF, JFM 13.53 Click for Nov-Mar GWO Phase Space Plot
2008-093 -0.596 -.783 SEPOCT -0.8 DJF 9.08 Click for Nov-Mar GWO Phase Space Plot
2010-11 -0.596 -2.037 AUGSEP -1.4 SON, OND, NDJ 20.20 Click for Nov-Mar GWO Phase Space Plot
2011-125 -0.370 -1.046 DECJAN -1.0 OND, NDJ 8.19 Click for Nov-Mar GWO Phase Space Plot
1. AAM and AAM tendency anomaly data not available.
2. Based on ONI values beginning with DJF 1949-50.
3. ONI did not meet threshold of 5 consecutive overlapping seasons.
4. MEI values are normalized and may change as new data is added. Specified values were current as of April 24, 2012.
5. Data as of April 24, 2012.

Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the period November 1 to March 31 of the following year. Data is from the GWO phase space data file linked on the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

Peak MEI: The peak seasonal value of the Multivariate ENSO Index (MEI). Reference Wolter and Timlin, 1993, 1998. MEI values are normalized and may change as new data is added.

Peak MEI Season: The peak bi-monthly season(s) for which the MEI is computed.

Peak ONI: The peak Oceanic Niño Index (ONI) based on SST anomalies in the Niño 3.4 region. Reference Climate Prediction Center Cold & Warm Episodes by Season.

Peak ONI Season: The peak tri-monthly season(s) for which the ONI is computed.

L.A. Rain: The water year precipitation total in inches for Downtown Los Angeles (USC). Reference NWS Los Angeles/Oxnard Downtown Los Angeles Climate Page, 1921-2006 Water Year Rainfall.

GWO Phase Space Plot: Plot of global relative atmospheric angular momentum anomaly vs. global relative atmospheric angular momentum tendency anomaly for the period November 1 to March 31 of the following year. Data is from the GWO phase space data file linked on the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

Tuesday, January 03, 2012 7:46:46 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, January 01, 2012

CPC 6-10 Day Outlook Precipitation Probability, issued Sunday, January 1, 2012 Click
CPC 6-10 Day Outlook Precipitation Probability
Issued Sunday, January 1, 2012

There's been no rainfall recorded at Downtown Los Angeles (USC) since December 17 when 0.01 inch recorded. Los Angeles ended December with 1.01 inch of rain. This is less than half of normal for the month and far less than last December's deluge of 10.23 inches.

Even though December 2011 was somewhat dry, it comes nowhere near setting a record. Since 1877 there have been eight Decembers in which no rain was recorded, and 44 Decembers with 1.01 inches of rain or less.

Downtown begins 2012 with a water year rainfall total of 3.76 inches. Last year we would have said this was near normal, but using the new normals derived from 1981-2010 data the total is 0.56 inch below normal. It has been several years since Downtown Los Angeles (USC) recorded below normal rainfall for the first six months of the water year. The last time was July 1 to December 31, 2007.

In a word the weather for the Rose Parade is expected to be SPECTACULAR. The current NWS point forecast for Pasadena is calling for an overnight low Sunday-Monday of 54 and a high Monday of 83. Click here for the latest NWS forecast for Pasadena.

The MJO has been relatively active this autumn and after going on a two week holiday appeared to be more coherent as it moved into the Western Pacific between Christmas and New Year's. However the NCEP GEFS and several other models forecast the MJO to rapidly diminish in amplitude and eastward propagation.

At the moment the precipitation outlook continues to be on the dry side. We'll see!

The November 30 - December 1, 2011 downslope windstorm felled thousands of trees, produced multi-day power outages and resulted in millions of dollars of damage in valley communities along the San Gabriel Mountains. An initial analysis of the conditions leading up to the event suggest a combination of factors contributed to the strength of the winds. Among them were a highly amplified and energetic north-south upper flow which was evolving into a cutoff upper low over southeastern California; a deepening surface low south of Las Vegas; cold air advection; and a possible inversion near mountain-top level.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Sunday, January 01, 2012 4:05:47 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Wednesday, November 23, 2011

Click
GOES-11 Water Vapor Image
Sunday, November 20, 2011 - 11:30 am PST

For the past two years Los Angeles has recorded above normal rainfall over the first six months of the water year (Jul. 1 to Dec. 31). So far this year is following suit.

After a record-setting storm in early October in which Downtown Los Angeles (USC) recorded over an inch or rain, a series of upper level troughs have continued to bump up the rainfall total. The systems have tended to be amplifying upper level troughs that split, typically transforming the southern half of the trough into a difficult-to-forecast cut-off upper level low. The resulting cut-off lows have then tracked over, along, or off the Southern California coast producing varying amounts of rain.

Sunday's system was the fourth to produce measurable rain in Los Angeles this November. A strong cold front produced very heavy rain, resulting in flooded streets and highways and resulting in a host of other weather-related problems. In the middle of it all runners in the PCTR Santa Monica Mountains 9K, 18K, 30K and 50K were running distances up to 31.5 miles on the trails of Pt. Mugu State Park.

Downtown Los Angeles (USC) recorded 0.90 inches for the storm, bringing the water year total to 2.75 inches. This is 1.11 inch above the new 1981-2010 normal for rainfall from July 1 through November 22. Here are some additional (preliminary) precipitation totals from around the area, compiled by the NWS Los Angeles/Oxnard. More than an inch above normal sounds like a lot, but as of today only guarantees Los Angeles precipitation will be above normal through December 12.

Back on July 1 NOAA released the new 1981-2010 climate normals, replacing the 1971-2000 normals that have been used this past decade. Normals serve as a 30 year baseline average of climate variables such as monthly and annual maximum, minimum, and mean temperature; and monthly and annual total precipitation. For example, Downtown Los Angeles' new normal annual precipitation total is now 14.93 inches, down from the 15.14 inches we've been using.

After dropping to -0.503 for July/August, and then to -0.772 for August/September, the September/October value of the Multivariate ENSO Index (MEI) has dropped a bit more to -.968 sigma. This is well within La Nina territory, but almost one sigma less than last year's September/October value. Plots of the Global Wind Oscillation (GWO) for July 1 to November 19, 2011 and the same period last year illustrate the year-to-year difference in the atmosphere's response to La Nina conditions. So far, this year's response is consistent with a more active MJO and a shift toward a more neutral ENSO state.

While there's still a chance of rain in Southern California Thanksgiving Day, the forecast is looking better than it did a few days ago when rain was considered likely. The difficulty in the forecast is yet another upper level trough splitting into a cut-off upper level low. The 12z NAM forecasts the low to remain offshore on Thanksgiving Day, and move into Northern Baja by the late afternoon. The 09z SREF puts the probability of more than 0.01 inch of rain in coastal Southern California for the 12 hours ending 4:00 pm Thursday at 10% - 30% and the chance of more than 0.10 inch of rain at around 10%. A shift in the track of the low toward the coast would significantly increase the chance of rain. We'll see!

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Wednesday, November 23, 2011 8:47:53 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Saturday, October 08, 2011

Click
GOES-11 Water Vapor Image
Wednesday, October 5, 2011 - 11:30 am PDT

An unseasonably deep upper level low, unusually strong 170+ kt Pacific jet, and associated cold front combined to produce record-setting rainfall in Southern California Wednesday, October 5. Rainfall totals exceeded 1.0 inch in many areas.

Downtown Los Angeles (USC) recorded 1.15 inches, setting a new record for the date, and kick-starting the area's rainy season to 0.78 inch above normal. Rainfall records for the date were also set for LAX, Long Beach, Camarillo, Santa Barbara and several other locations. It was the first measurable rainfall at Los Angeles since June 17. Here are some preliminary precipitation totals from the NWS Los Angeles/Oxnard,NWS San Joaquin Valley/Hanford and NWS San Diego.

Enhanced convection in the Western Pacific associated with active phase of the MJO, and an extension of the North Pacific Jet caused by a positive East Asian mountain torque event appeared to have contributed to the unseasonable amount of rainfall. As observed by Ed Berry (Atmospheric Insights, Dec. 30, 2007), "...the MJO itself does not generate enough extratropical westerly wind flow to allow the East Asian jet to impact the USA west coast. A strong positive East Asian mountain torque needs to be involved, on average."

The increase in relative AAM shown by the GWO not withstanding, La Nina conditions appear to be consolidating in the equatorial Pacific. This four month sequence of Pacific Ocean Equatorial Temperature anomaly cross sections shows substantial subsurface cooling from July 11 to September 11. The Multivariate ENSO Index (MEI) has dropped from -0.5 for July/August to -0.8 for the August/September season. This drops the MEI from a rank of 16th last month to 13th this month, just above the quintile definition of a moderate La Niña ranking. Last year the MEI for August/September ranked 1st in the record since 1950. This TAO time-longitude plot of SST and SST anomaly shows less cooling than last year on this date.

To get an idea of what the impact of a second year La Nina might be on 2011-12 Winter precipitation in the continental U.S., the ESRL/PSD US Climate Division Dataset Mapping Page was used to construct a map of US composite precipitation anomalies for November to March for year two La Ninas since 1949. The years included were based primarily on MEI rankings, and include 1950-51, 1955-56, 1962-63, 1971-72, 1974-75, 1999-2000 and 2008-09. The base period was 1971-2000.

For this selection of years the coastal Southern California climate division recorded about 5 to 6 inches less precipitation than normal for the period November through March. The percent of normal water year rainfall recorded at Downtown Los Angeles (USC) ranged from a low of 47% (1971, 7.17"), to a high of 106% (1955, 16.00"). The average rainfall at Los Angeles for these years was 70.5% of normal, or 10.7".

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Saturday, October 08, 2011 2:05:22 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, September 12, 2011

Click
GOES-11 Water Vapor Image
Saturday September 10, 2011 - 6:30 pm PDT

A dynamic cutoff upper low centered over Southern California produced numerous thunderstorms in Southern California and a broad area of the southwestern U.S. Saturday. The thunderstorms produced thousands of lightning strikes, some heavy downpours, hail and strong winds.

According to an article on Yuba.net over 15,000 lightning strikes were recorded in California over the 24 hour period ending 0600 PDT Sunday. This plot of lightning detections was produced by Tahoe National Forest. (Typically lightning detections include both cloud-cloud and cloud-ground strokes.)

Thunderstorms were widespread in Southern California and several strong thunderstorms were reported by the NWS. This NWS NEXRAD image from about noon on Saturday shows several strong cells including one area flagged as severe. This composite image from WSI/Intellicast.com at 2:45 pm PDT shows estimated cloud tops, cell movement and hail. Half inch hail was reported in several locations by NWS spotters and there was one report of 1.25 inch hail near Lake Los Angeles. A wide swath of enhanced thunderstorm activity developed in the afternoon to the north and northeast of Los Angeles.

Some of the higher rainfall totals reported by the NWS include Lake Palmdale at 0.98 inch; Palmdale 0.84 inch and Lockwood Valley 0.58 inch. Downtown Los Angeles recorded a trace. Here's a NWS Los Angeles/Oxnard tabulation of some rainfall totals from around the area. Here also is a NWS San Joaquin Valley/Hanford tabulation of some rainfall totals in the southern San Joaquin Valley and Sierra.

In a Southern California Weathernotes post in February I commented that the tough question regarding La Niña was whether warming would continue into the NH summer, with neutral ENSO conditions prevailing as we move into autumn; or if the ENSO cycle would swing back toward a La Nina state. It was noted that since 1949, about half of the first year La Nina episodes have continued into a second or third year.

Climate scientist and Multivariate ENSO Index (MEI) codeveloper Klaus Wolter first mentioned the roughly 50/50 chance that La Nina would return following a summer respite in September 2010. A glance at a plot of the extended MEI index, going back to 1871 clearly shows a propensity for a return of La Nina in the year (or years) following stronger La Nina episodes.

In a September 8, 2011 press release NOAA reported that La Nina is back. More precisely, in their September 8 ENSO Diagnostic Discussion CPC states "La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12." The Multivariate ENSO Index (MEI) has dropped below the weak La Nina threshold, and several oceanic and atmospheric factors are indicative of a reemerging La Nina. There's still a (historically) slight chance of a return to ENSO neutral conditions this fall, but it doesn't appear likely. We'll see!

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Monday, September 12, 2011 1:39:58 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Thursday, June 30, 2011

Click
GOES-11 Water Vapor Image
Tuesday June 28, 2011 - 2:30 pm PDT

Tuesday a front associated with an unseasonably strong Pacific low pressure system broke rainfall records in much of the northern half of the state. Precipitation records for the date were broken in numerous locations, including Monterey, San Jose, Oakland, San Francisco, Napa, Sacramento, Redding, Eureka and Crescent City. Here are archived copies of record reports from the San Francisco Bay/Monterey NWS Office and the Sacramento NWS Office.

The front and trough produced a few clouds and cooled temperatures in the Los Angeles area, but I didn't see any reports of rain. Downtown Los Angeles (USC) will end the July 1, 2010 to June 30, 2011 water year with 20.20 inches of rain. This is about 133% of the climate normal of 15.14 inches. According to NWS data Camarillo/Oxnard recorded 139% of normal rainfall, Long Beach 145%, Santa Barbara 169% and Palmdale 105%.

Looks like temperatures will be warming up for the July 4th weekend. Temperatures are expected to reach into the 80s at the coast, 90's inland and 100's in the valleys. Desert areas could reach 110 or higher. Models suggest the possibility of some monsoon moisture moving into the area Sunday or Monday, along with a chance of thunderstorms in the mountains and deserts. Check the NWS Los Angeles/Oxnard Office for the latest forecasts and warnings.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Thursday, June 30, 2011 3:30:58 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, June 07, 2011

Click
Aqua-MODIS Composite Satellite Image (NRL)
Saturday, June 4, 2011

An unseasonably strong Pacific low pressure system that stalled about 200 NM off the Central Californio coast set new rainfall records from San Francisco to Santa Barbara over the weekend. The N-S oriented front associated with the system was positioned over Santa Barbara and San Luis Obispo counties much of the weekend, resulting in unusually high rainfall totals in some areas. Midday Sunday the upper low began to move east along 35°N, increasing divergence aloft in areas north of Pt. Conception and producing additional precipitation Sunday afternoon and evening.

Saturday a new rainfall record for the date was set in San Francisco; and on Saturday and Sunday new rainfall records were set in Stockton, Modesto, Paso Robles and Santa Maria. Sunday Santa Barbara Airport recorded 1.24 inches of rain, breaking the record for the date, and increasing the station's rainfall total for June to the highest since recordkeeping began in 1941. The dissipating front produced some scattered showers in the Los Angeles area Sunday.

There were some impressive storm totals. Nordhoff Ridge, in Ventura County, recorded 1.07 inches of rain; Refugio Pass, in Santa Barbara County, 2.64 inches; and Rocky Butte, in San Luis Obispo County, 3.94 inches. Downtown Los Angeles (USC) recorded a trace of rain on Sunday, leaving our water year (July 1 to June 30) rainfall total at 20.19 inches. Here is an archived copy of a NWS Los Angeles/Oxnard compilation of some rainfall totals from around the area.

Saturday I did a trail run on the 8000-9000 ft. ridge between Mt. Pinos and Mt. Abel, north of Los Angeles, and was able to observe first-hand the very strong southerly flow associated with this system, and the spectacular wave clouds that resulted.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Tuesday, June 07, 2011 11:43:44 AM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, May 16, 2011

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BUFKIT - Precipitation and Temperature Forecast
WRF Ensemble for VNY 05/16/11 12z

Overall it's been a wet water year in Southern California, but in the fashion of a Mediterranean climate the wet water year has been comprised of a patchwork of wet and dry months.

If it were not for an unusually stormy December in which Downtown Los Angeles recorded 8.32 inches more rain than normal, Los Angeles would be looking at about 76% of normal rainfall this water year instead of 131%. This reduced amount would be more typical of the rainfall recorded in Los Angeles during a La Nina influenced water year.

March was wet, but April and May have been dry. Sunday morning's wet weather added 0.07 inch to May's total for Los Angeles, but the combined April/May rainfall deficit is still about 0.9 inch.

BUFKIT analysis of WRF ensemble data for Van Nuys and LAX suggests tomorrow's storm is likely to produce between 0.1 inch and 0.3 inch of rain in the Los Angeles basin, and perhaps up to 0.4 inch in the San Fernando Valley. SREF Ensemble probabilities and HPC Probabilistic Precipitation Guidance support this estimate.

It won't take a lot of rain to break the record for May 17 at Downtown Los Angeles -- 0.18 inch would do it -- and it would also raise the water year rainfall total for Los Angeles to over 20 inches. The previous precipitation record for May 17 was 0.17", set in 1883. Note: Record for USC Campus (KCQT) is 0.06, set in 1949, but data from Civic Center is used for Downtown Los Angeles records prior to 1921.

There's a chance of more rain Wednesday, and then perhaps again Sunday into Monday. We'll see!

Update Tuesday, May 17, 2011. Rainfall amounts from the storm that affected Los Angeles last night and this morning were generally within the range projected by the WRF ensembles. Downtown Los Angeles (USC) recorded 0.15 inch for the storm, bring the water year total to 19.99 inches. Here's a report compiled by the NWS with some rainfall totals from around the area. Tonight's system is forecast to produce similar rainfall totals. At the moment some drizzle or light rain looks like a possibility in the Los Angeles area Sunday and early Monday.

Update Wednesday, May 18, 2011. Thanks to the system that moved into the area last night, Downtown Los Angeles (USC) recorded additional rainfall Tuesday evening, nudging the rainfall total for May 17 up to 0.18 inch, and breaking the old rainfall record for the date set in 1883. Shower activity appears to be winding down and partly cloudy skies are forecast for Los Angeles this afternoon. Rainfall totals from the second system were generally similar to Tuesday's amounts. Here's a report compiled by the NWS Los Angeles/Oxnard that lists the cumulative rainfall that has resulted from these two storms for a number of stations around the area. The water year total for Downtown Los Angeles (USC) now stands at 20.19 inches.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Monday, May 16, 2011 7:32:59 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   |