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# 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  |   | 
# Sunday, January 1, 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 1, 2012 4:05:47 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Wednesday, November 23, 2011

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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  |   | 
# 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  |   | 
# Friday, March 18, 2011

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HPC 3-Day Precipitation Forecast
For the Period Ending 11:00 a.m. Monday, March 21

Along with January and February, March is one of the big three precipitation months in Southern California in which the average rainfall for Downtown Los Angeles exceeds 3.0 inches. In January we were about 2.5 inches below normal rainfall, and in February about 0.4 inch below normal. So far this March, we're nearly two inches below normal for the month. If it were not for an unusually wet December in which Los Angeles recorded 8.32 inches above normal rainfall, we'd be looking at 50% water year right now instead of over 100%.

If today's 12z NAM and GFS forecasts verify, we could make up that March deficit, and push our water year total up to nearly 120%! According to these numerical forecasts, we could see two to three inches of rain in the Los Angeles area by Monday afternoon, and significantly more in orographically favored foothill and mountain locations. The NAM forecasts moist southerly winds approaching 60 kts at the 5000 ft. level Sunday evening.

BUFKIT analysis of 12z NAM/GFS data generates 2.16/4.11 inches of rain for LAX, 3.56/3.57 inches for Van Nuys, and 4.01/4.20 inches for Santa Barbara. The GFS brings in the second front faster than the NAM, forecasting the onset of heavier rain during the day Sunday, rather than Sunday evening. The 09z SREF puts the probability of more than 1.0 inch of rain in the Los Angeles area for the 24 hour period ending Monday morning at about 90%.

And yes, it does look like there's a chance of rain for the Los Angeles Marathon. Although the heavies rain is forecast to hold off until Sunday afternoon or evening, the 09z SREF pegs the probability of 0.1 inch of rain or more in the Los Angeles area over the 6 hours ending at 11:00 a.m. Sunday at about 70%. BUFKIT analysis of 12z NAM data generates about 0.20 inch at LAX from 8:00 a.m. to noon, with temps in the mid 50's. The GFS says about 0.50 inch over the same period. We'll see!

Be sure to check the NWS Los Angeles/Oxnard web site for the latest forecasts, advisories and warnings. More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Friday, March 18, 2011 11:41:41 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, February 21, 2011

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Experimental HPC 6-Hour Probabilistic Precipitation Guidance
For the 6 Hour Period Ending 4:00 p.m. Tuesday

The rainfall totals from Friday's and Saturday's systems were generally a little below the 2 inches forecast, but it was still enough to boost the water year rainfall total for Downtown Los Angeles to 14.58 inches. This is about 96% of the normal water year total of 15.14 inches. The water year extends from July 1 to June 30, so we still have four months to receive the 0.56 inch of rain that would put us at 100%. Here's an archived copy of a NWS tabulation of some rainfall totals from around the area from early Thursday morning to 10:00 a.m. Sunday.

Southern California's wet weather pattern didn't extend into this week as it looked like it might. The upper low that might have produced the rainfall is now forecast to stay offshore. At the moment it looks like it will mainly result in some clouds as it moves down the coast today through Wednesday. Rain chances increase near the end of the week and into the weekend as an upper low and trough work down the West Coast. Ensemble members vary quite a bit on the track of the upper low, with some solutions wetter in Southern California than others. We'll see!

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

Monday, February 21, 2011 2:28:03 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, February 17, 2011

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HPC 3-Day Precipitation Forecast
For the Period Ending 4:00 a.m. Sunday Morning

The transition from a persistent West Coast ridge to a West Coast trough occurred on Monday more or less as forecast by medium range guidance back on February 5. A series of systems and impulses riding up and over a high amplitude Eastern Pacific ridge are expected to continue to produce cool, blustery weather in Southern California with periods of showers and rain into next week.

Precipitation on Valentine's Day was generally limited to areas north of the Los Angeles basin, but was a little more widespread late Monday night into Tuesday morning, with a number of stations in the Los Angeles area recording a few hundredths of an inch of rain.

Wednesday's system was much more energetic. Because of the convective nature of the precipitation, rainfall amounts were extremely variable, ranging 0.25 inch or less to 1.0 inch or more. Downtown Los Angeles (USC) recorded 0.65 inch of rain for the storm, bringing the water year total for Los Angeles to 13.14 inches. This is well above normal for the date, and about 87% of normal for the water year. Here's an archived copy of a NWS tabulation of some rainfall totals for the period 4:00 p.m. Tuesday to 4:00 a.m. Thursday.

Los Angeles only needs about 2 more inches of rain to top the 100% mark for the water year, and it looks like we could get most of that Friday and Saturday. BUFKIT analysis of 12z NAM data for Van Nuys indicates about 1.6 inches of rain Friday into Saturday, and then another 0.5 inch Saturday night. The HPC 3-day Quantitative Precipitation Forecast for the period ending 4:00 a.m. Sunday also indicates about 2.0 inches of rain in Southern California. This morning's 09z SREF puts the probability of more than 1.0 inch rain for the 24 hour period ending 1:00 p.m. Saturday at about 70%.

Temperature data at the surface and at depth in the equatorial Pacific suggest the La Nina is moderating. The tough question is whether warming will continue into the NH summer, with neutral ENSO conditions prevailing as we move into autumn; or if the ENSO cycle will swing back toward a La Nina state. Since 1949, about half of the first year La Nina episodes continued into a second or third year. At the moment the majority of computer models favor a transition to ENSO neutral or warm conditions by July 2011. Here is a compilation of ENSO Forecasts from the IRI ENSO Quick Look for February 17, 2011. We'll see!

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

Thursday, February 17, 2011 1:31:48 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Saturday, February 5, 2011

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NCEP Ensemble Forecast
240 hr. Forecast for February 14 at 4:00 p.m. PST

Although the Pacific jet did expand as anticipated through about January 27, and then retract around January 29, leading to a upper low off the California coast, it wasn't the discontinuous ridge regression which had been hoped for -- or the change in pattern that would open the door to Pacific storms wishing to visit sunny Southern California.

The area did manage to get a bit of rainfall out of the system. Downtown Los Angeles (USC) recorded 0.21 inch on Sunday, bringing the rainfall total for January up to a paltry 0.79 inches, which is more than 2.5 inches below normal for the month. At this point Downtown Los Angeles remains almost 5 inches above normal for the water year (July 1 to June 30), but with each dry day that cushion grows a little smaller. Here's an archived copy of a NWS tabulation of some rainfall totals from last Sunday's storm.

Well, what the MJO couldn't do maybe random influences will. Both the GFS and ECMWF are forecasting a change to a wetter pattern for California around Valentine's Day. This is supported by the NCEP Ensembles, and ESRL/PSD Analog Probabilistic Precipitation Forecasts for the 8-14 day period. As this CPC 8-14 day Precipitation Outlook indicates, the chances look the best from Central California, north into Oregon. We'll see!

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

Saturday, February 5, 2011 4:48:56 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, January 20, 2011

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Extended Pacific Jet and Resulting Mega-Ridge
GFS Forecast for Sunday Afternoon

Over the next two weeks, the MJO signal currently propagating across the western Pacific is forecast to destructively interfere with the La Nina base state, suppressing convection in the Indian Ocean and Indonesia and enhancing convection near the dateline. This is forecast to result in a transition from upper tropospheric anomalous cyclones to anticyclones near the dateline, and an extension of the East Asian/Pacific jet. These circulation changes may eventually lead to a retrogression of our persistent West Coast ridge, or perhaps a breakthrough of the westerlies underneath the highly amplified ridge.

The key word here is eventually. Over the next week or so, the extending Pacific jet is forecast to reamplify the ridge over the West Coast. But at some point, perhaps near the beginning of February, destructive interference in the Western Pacific will dwindle and convection in the Indian Ocean will strengthen. This should result in retraction of the Pacific jet, and possibly, a West Coast trough. The 240 hr forecast of the 12z ECMWF hinted at this possibility, as did the 18z GFS. We'll see!

After starting out cold and wet, the weather this January in Southern California, and much of the state, has been warm and dry. Monday, Pierce College in Woodland Hills hit a high of 88°F, and Downtown Los Angeles (USC) 84°F. So far this January, only 0.58 of rain has been recorded at Downtown Los Angeles (USC), which is a little less than one-third of normal for the month. However, because of our prodigious December rainfall the water year total at Los Angeles is currently 6.5 inches above the normal for the date of 5.78 inches.

Earlier this month I photographed these mid-level mammatus clouds over the western San Fernando Valley. They were produced by the moisture and dynamics associated with a closed upper level low that was about 390 miles WSW of Los Angeles. To see how the clouds evolved and more about the scenario at the time, see this post on PhotographyontheRun.com.

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

Thursday, January 20, 2011 7:25:42 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   |