# Monday, July 01, 2013

Western U.S. Precipitation - Percent of Average (WRCC) for July 1, 2012 to June 30, 2013. Click
Western U.S. Precipitation - Percent of Average (WRCC)
July 1, 2012 to June 30, 2013.

Downtown Los Angeles (USC) finished the water year (July 1 to June 30) with only 5.85 inches of recorded rainfall, making it the sixth driest water year since recordkeeping began in 1877. With a deficit of over 9 inches, the water year rainfall total was about 39% of the norm of 14.93 inches. This tabulation of Rain Season Totals from the NWS/Oxnard shows rainfall totals around the area ranged from a low of 14% of normal at Palmdale Airport to a high of 54% at Long Beach Airport and LAX.

As this WRCC precipitation map for the period July 1 to June 30 shows, below average precipitation was not limited to Southern California. If it were not for heavy precipitation related to atmospheric river events in late November/early December there would be even more red on the map.

It has been even drier since January 1. For example, since January 1 Downtown Los Angeles has received only 25% of normal rainfall; Burbank 21% of normal; LAX 30% of normal; Santa Barbara 28% of normal; and Palmdale 19% of normal. Surprisingly, rainfall totals for Los Angeles since January 1 are only the ninth driest on record. The driest January-June on record was 1972 when 0.26 inch was recorded. And guess what -- we went on to have a very wet rain season in 1972-73 with 21.26 inches of rain in Los Angeles!

As dry as it's been in the Los Angeles area since the first of the year, it has been drier at some locations in the San Francisco Bay Area. Remarkably, LAX has had more rain than SFO, and Burbank Airport in the San Fernando Valley has had more rain than Napa Airport in the Napa Valley!

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

Monday, July 01, 2013 3:09:39 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, December 08, 2012

MIRS Integrated Water Vapor, December 2, 2012 1800 UTC for the preceeding 12 hours. Click
MIRS IWV All Satellites
December 2, 2012 1800 UTC Preceding 12 hours.

If you were to only look at the Global Wind Oscillation (GWO) for November you might think our 2012-2013 El Nino hadn't flopped. The relative AAM anomaly peaked at about 1.4 around November 20, which is the highest it's been since the El Nino of 2009-2010.

Most of the AAM was added in the NH between 15°N and 30°N. This led to the development of a high amplitude mid-Pacific ridge, and undercutting of the ridge by the westerlies. This enabled a low near the dateline to tap tropical moisture and relay it into the circulation of a large eastern Pacific low. This linkage provided the moisture necessary to create the atmospheric rivers that produced excessive precipitation in Northern and Central California last week.

Over the 5-day period ending Monday morning (December 3) Northern and Central California recorded double-digit precipitation totals with several stations recording rainfall amounts in excess of 15 inches. Here are archived Public Information Statements issued by NWS San Francisco Bay Area/Monterey and NWS Eureka with some of the phenomenal precipitation totals recorded in those areas. This AHPS Precipitation Analysis shows the observed precipitation in the western U.S. for the 7-day period ending Monday morning.

New forecast methods developed by NOAA's ESRL PSD using satellite-derived and GFS medium range forecast data indicated high levels of water vapor transport early Friday and early Sunday. This typically characterizes AR events. This Evaluation of GFS Forecast Fields (PDF) shows the observed Integrated Water Vapor (IWV) for December 2, the corresponding analysis, and the 1-day to 5-day forecasts.

System dynamics were much weaker in Southern California, and the IWV content of the atmospheric rivers was less. (Friday IPW and Sunday IPW). Even so orographically favored areas were still able to wring several inches of rain from the moist flow. From Tuesday night to Monday morning Opids Camp recorded 3.02 inches, White Ledge Peak 4.09 inches, Refugio Pass 4.61 inches, and Rocky Butte 8.51 inches.

Over the same period Downtown Los Angeles (USC) recorded 1.03 inches, bringing the water year total to 1.36 inches. As of today that's 1.08 inch less than normal. Here's an archived copy of a NWS compilation of preliminary rainfall totals in our area.

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

Saturday, December 08, 2012 5:30:17 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, October 12, 2012

Click
Cut-off Upper Level Low
GOES-15 Water Vapor Image - 1:30 p.m. Thursday.

Instability associated with a cut-off upper level low resulted in scattered strong thunderstorms and widespread showers in Southern California on Thursday. A GOES Sounding 8 nm NW of KLAX at 3:00 pm indicated an LI of -4 and CAPE of 836.

According to NWS Storm Reports a spotter in Simi Valley area near Tapo St. and the 118 Frwy reported 1.0 inch of rain in 15 minutes and 1.5 inches in 30 minutes with street flooding. A Mesonet station in Simi Valley recorded 0.84 inches of rain in 12 minutes. A Mesonet station near Pasadena recorded 1.1 inches in 25 minutes. Long Beach Airport set a new rainfall record for the date of 0.30 inches.

The rain gauge at Downtown Los Angeles (USC) dodged all but a few rain drops, recording 0.01 inch for the storm. Here's an archived copy of a NWS compilation of preliminary rainfall totals across the area.

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

Friday, October 12, 2012 4:53:51 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, September 29, 2012

In a post last June I mentioned that the atmosphere wasn't responding to warming Pacific equatorial SSTs. At that time normalized relative AAM values had dropped to around -2 sigma. Although El Nino-like SST conditions developed in the equatorial Pacific in July and persisted in August, the atmospheric component (AAM) did not follow suit. The average AAM for the period July-September was less than any other El Nino year going back to 1950. (See chart below.)

Following a relative rapid 2 sigma increase over a period of six months, the July/August value of the Multivariate ENSO Index (MEI) dropped from 1.139 to 0.579, and its rank for the season dropped from just below a 'strong' El Nino to just below a 'weak' El Nino. Over the last month SST Anomaly in Nino Region 3.4 has dropped 0.6°C. A review of the ONI record reveals that a drop in the index, which is based on a 3 month running mean of Nino 3.4 anomaly, has not occurred before the Sep-Oct-Nov season during a warm episode.

As of mid September most models were still forecasting development of weak El Nino conditions. The IRI/CPC Plume-based ENSO Forecast puts the probability of El Nino conditions in the Sep-Oct-Nov season at a little over 80%! The probability of Neutral conditions is pegged at a little under 20%. The chance of returning to La Nina conditions is considered virtually nil. Going back to 1950, year two La Nina conditions almost always transition either back to La Nina conditions or to El Nino conditions. Depending on the climatology used there is either one (1985-86) or no cases of a transition to Neutral conditions from a second year La Nina.

Many dynamical model MJO forecasts are predicting a developing MJO signal in the Western Pacific, and that appears to be occurring. Velocity potential loops and Pacific Basin stitched satellite imagery show enhanced convection west of the date line, and today's MJO phase space plot from CAWCR/BOM shows a signal beginning to emerge. On the wind side, Mountain torques are over +4 sigma and Coriolis torque is at -2 sigma. Whether the (apparently) emerging MJO will help reboot our fading El Nino remains to be seen.

Update Friday, October 5, 2012. Eastward-propagating MJO-like signal didn't evolve as forecast by GFS (and several other models). Here's today's MJO phase space plot from CAWCR/BOM. Large swings in the magnitude of Mountain and Coriolis torques have continued. Relative AAM remains at about -1 sigma. The Early October CPC/IRI Consensus Probabilistic ENSO Forecast indicates an increasing chance of Neutral conditions developing over the next several months, but still gives an edge to El Nino conditions developing before the end of 2012.

Following is a chart comparing 2012-13 to warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised Oceanic Niño Index (ONI) based on multiple-centered 30 year base periods and are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. A description of the parameters follows the chart. With the exception of years prior to 1957, a GWO phase space plot is included for each warm episode.

Year Jul-Sep
AAM
Nov-Mar
AAM
Peak MEI Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1951-521 -- -- 0.853 JULAUG 1.2 SON 26.21 --
1952-533 -- -- 0.840 APRMAY 0.7 MAM 9.46 --
1953-543 -- -- 0.522 AUGSEP 0.8 ASO,SON,OND 11.99 --
1957-58 -- 0.773 1.473 DECJAN, JANFEB 1.8 NDJ, DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-592 -0.919 -0.206 0.803 JANFEB 0.6 NDJ, DJF,JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.005 0.046 0.857 OCTNOV, DECJAN 1.4 OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.826 -0.748 1.483 JULAUG 1.9 SON,OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-694 0.130 0.513 0.868 JANFEB 1.1 DJF, JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-704 0.358 0.413 0.644 OCTNOV 0.9 SON,OND 7.77  
1972-73 -0.096 -0.239 1.886 JUNJUL, JULAUG 2.1 OND,NDJ 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.284 -0.828 1.027 AUGSEP 0.8 OND,NDJ 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.646 1.008 1.007 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.938 2.337 3.037 FEBMAR 2.2 NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.232 0.019 2.122 APRMAY 1.3 JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.153 1.000 1.951 JULAUG 1.6 JAS, ASO 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.008 0.808 2.271 MARAPR 1.6 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.422 0.764 1.434 SEPOCT 1.2 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.811 1.481 3.001 JULAUG,AUGSEP 2.4 OND 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.047 0.324 1.184 DECJAN 1.3 OND,NDJ 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.020 0.747 1.018 FEBMAR 0.7 JAS-NDJ 37.96 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.143 -0.322 1.289 OCTNOV 1 OND, NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.103 0.303 1.520 JANFEB 1.6 NDJ,DJF 16.36 Click for Nov-Mar GWO Phase Space Plot
2012-136 -0.951 0.296 1.139 JUNJUL 0.6 SON 5.85 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. AAM anomaly is average for Jan-Mar 1958.
3. Continuous warm episode from DJF 1952/53 to JFM 1954.
4. Continuous warm episode from JAS 1968 to DJF 1969/70.
5. Continuous warm episode from JAS 1986 to JFM 1988.
6. Data as of May 8, 2013.

Jul-Sep AAM & Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the periods July 1 to September 30 amd 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 (Multiple centered 30-year base periods.)

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.

Saturday, September 29, 2012 3:15:07 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, June 30, 2012

TAO/TRITON Time-Longitude Plot SST and Anomaly Click
TAO/TRITON Time-Longitude Plot of SST and Anomaly
Saturday, June 30, 2012

Downtown Los Angeles (USC) will end the the 2011-2012 water year (July 1 to June 30) having recorded 8.69 inches of rain. This is about 58% of the 1981-2010 normal of 14.93 inches. The deficit of 6.24 inches is a little more than the 5-6 inch deficit recorded in a selection of similar second year La Nina years. According to data compiled by the NWS Santa Barbara will end the water year at about 66% of normal; Camarillo/Oxnard at 57%; Burbank Airport at 51%; LAX at 59%; and Long Beach Airport at 62%.

This TAO/Triton plot of Pacific equatorial SST and anomaly clearly depicts the evolution of our two year La Nina and the recent transition to warmer conditions. Is an El Nino in the works for this Winter? According to the Multivariate ENSO Index (MEI) a transition to El Nino conditions may already be underway. The April/May value of the MEI was +0.706. This is already within the range of a weak El Niño ranking. In his June 6 discussion of the MEI climatologist Klaus Wolter noted the last month's increase in the MEI was the 6th highest increase for this time of year since 1950. He also pointed out that it was the 4th monthly increase of this caliber in a row -- second only to the record of six consecutive large monthly increases in 1997 at the beginning of the mega El Nino of 1997-98. It will be very interesting to see if the string of large increases in the MEI continues with the May/June value.

While the ocean seems to be on board with the El Nino idea, the atmosphere appears to be balking -- at least for the moment. As of June 24, the AAM component of the GWO was down around -2.0, which is nearly as low as it's been during year two of the 2010-2012 La Nina. A positive value of AAM is generally associated with El Nino conditions.

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

Saturday, June 30, 2012 4:27:44 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, April 30, 2012

NCAR NEXRAD Composite Regional Radar Image from Wednesday, April 25, 2012 at 9:57 pm PDT Click
NCAR NEXRAD Composite Regional Radar Image
Wednesday, April 25, 2012 at 9:57 pm PDT

Judging from this NEXRAD regional composite radar image last week's system might have been much wetter. As has happened a couple of times this season, much of the heavier rain appears to have remained offshore. Even so, this compilation of rainfall totals from around the area by the NWS Los Angeles/Oxnard lists some respectable rainfall totals for a late season storm in Southern California.

Downtown Los Angeles (USC) recorded 0.49 inch for the storm, increasing April's rainfall total to 1.71 inches. This is almost double April's normal of 0.91 inches. The water year total rainfall for Downtown Los Angeles now stands at 8.68 inches; which is about 60% of normal at this point in the water year. The water year extends from July 1 to June 30.

In a "normal" season Los Angeles would be expected to record another 0.35 inch of rain by June 30. Both the 6-10 Day Precipitation Outlook and 8-14 Day Precipitation Outlook from the CPC are indicating a better chance of below normal precipitation in Southern California than of normal or above normal precipitation. The CPC Monthly and Three Monthly Temperature and Precipitation Outlooks are indicating an equal chance of above normal, normal, and below normal precipitation in Southern California. We'll see!

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

Monday, April 30, 2012 1:38:49 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, April 14, 2012

WSI Intellicast.com Composite Radar Image from Friday, April 13, 2012 at 11:00 am PDT Click
WSI Intellicast.com Composite Radar Image
Friday, April 13, 2012 at 11:00 am PDT

Some of the video of yesterday's rainstorm looked more like coverage of a hurricane rather than an April storm in Los Angeles. There were flooded streets and creeks, lightning strikes of aircraft and gas lines, strong winds, waterspouts, hail, toppled trees, mountain snow and more. Downtown Los Angeles (USC) set a new rainfall record for the date of 0.49 inches, breaking a record set in 1956.

The system's strong dynamics were due in part to upper level divergence associated with an ideally positioned jet max and strong positive vorticity advection. The result was strong omega, with 12z NAM vertical velocities at KVNY on the order of -25 microbars per second from 900 mb to 600 mb.

Apirl's above average rainfall has increased the water year (July 1 to June 30) rainfall total for Downtown Los Angeles to 8.19 inches, which is about 58% of normal. Here are some preliminary rainfall totals from around the area for the storm earlier in the week and yesterday's storm compiled by the NWS, and a snapshot of a Ventura County Watershed Protection District Google Map (large image) with some rainfall totals for the past week.

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

Saturday, April 14, 2012 1:49:05 PM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Thursday, March 29, 2012

NRL GOES-15 Visible/IR Satellite Image from Sunday, March 25, 2012 at 1:31 pm PDT Click
NRL GOES-15 Visible/IR Satellite Image
Sunday, March 25, 2012 at 1:31 pm PDT

Low pressure "alow and aloft" and associated surface boundaries resulted in some higher than expected rainfall totals Sunday. Gauges in the Santa Monica Mountains generally recorded from 2-3 inches of rain, Valleys and the Metro area 1-2 inches, and Los Angeles County mountains 1-2.5 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 with some additional rainfall totals.

Downtown Los Angeles (USC) recorded 0.95 inch for the storm, bringing the 2011-2012 water year total to 6.93 inches. This boosts the water year total to 51% of normal. The wet weather the last two weekends makes March the wettest month of the rain season to date at Los Angeles. It may have taken the edge off a very dry rain season for the moment, but rainfall totals the past 30 days have still been below normal in much of Southern California and additional rainfall would really help.

The good news is it looks like the current progressive pattern of West Coast troughs will continue into April. While at the moment it appears the next trough in the series won't produce more than a smattering of rain south of Pt. Conception, the ECMWF has been relatively consistent in bringing in a system similar to our last storm weekend after next. That's a long way out, and the GFS and GEFS don't agree with the ECMWF, but we'll see!

Update 04/02/12. Saturday's system produced a little more rain than expected south of Pt. Conception. Downtown Los Angeles (USC) recorded 0.04 inch for the storm, bringing the 2011-2012 water year total to 6.97 inches. Here are some rainfall totals from around the area compiled by the NWS. At the moment it looks like a disturbance rotating around a large Gulf of Alaska low will probably not elongate and deepen the low enough to produce rain in Southern California, but will result in cooler temperatures Wednesday and Thursday. Higher pressure is forecast to build in behind the trough, with a warming trend forecast through Easter weekend.

According to the Australian Bureau of Meteorology ENSO Wrap-up, issued March 27, the 2011–12 La Niña event has ended, with key indicators returning to neutral levels.

The IRI/CPC mid-March plume of forecasts made by dynamical and statistical models for SST in the Nino 3.4 region suggest ENSO Neutral conditions will persist through boreal autumn 2012. However, as climatologist Klaus Wolter points out, all ten of the two-year La Niña events between 1900 and 2009 either continued as a La Niña event for a third year (four of ten), or switched to El Niño (six of ten), with none of them becoming ENSO-neutral.

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

Thursday, March 29, 2012 10:32:16 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# 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  |   |