An experimental PSD forecast issued November 19, 2013 for the period December 2013 through February 2014 prepared for the California DWR by Dr. Klaus Wolter of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado shows a significantly increased chance of less than normal precipitation in most of Southern California and the Central San Joaquin Valley. The forecast guidance shows the shift in tercile probabilities for precipitation, similar in concept to the NOAA CPC precipitation outlooks.

According to Dr. Wolter the statistical forecast scheme integrates as many of the known influences on California's climate as possible, using data from 1950 onwards. In the absence of El Nino and La Nina influences considerations such as the status of the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO), or recent Alaskan temperatures can be evaluated through statistical models to make a forecast.

Dr. Wolter also produced composite precipitation anomalies for the periods October-December and January-March for years with comparable PD0-AMO indices. In Southern California the Oct-Dec anomalies were -0.5 to -0.7 SD below the 1895-2000 Longterm Average and the Jan-Mar anomalies were -0.1 to -0.3 SD below average.

Since October 1 precipitation in California, Oregon and Washington has generally been well below normal. As of today the precipitation recorded at Downtown Los Angeles is at about 30% of normal for the water year (July 1-June30). If Los Angeles doesn't record more than 0.58 inch of rain over the remainder of December, 2013 will rank as the driest calendar year on record.

A wildcard in the California precipitation outlook is the occurrence of atmospheric rivers such as those that occurred at the end of November 2012 and during December 2010. An analysis of all winter ARs in California during WY1998–2011 presented in the paper The 2010/2011 snow season in California's Sierra Nevada: Role of atmospheric rivers and modes of large-scale variability by Bin Guan, et.al., found that atmospheric river frequency is increased during negative phases of the Arctic Oscillation (AO) and the Pacific-North American (PNA) teleconnection patterns.

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Updated November 5, 2013. My mistake -- a spreadsheet range error -- thanks for the heads up Reg! The driest January 1 to November 1 for Downtown Los Angeles was in 1972 with 0.92 inch. Here are the driest ten years for that period:

1. 1972 0.92
2. 2002 1.62
3. 1984 1.93
4. 1961 2.37
5. 1971 2.39
6. 1947 2.45
7. 2013 2.78
8. 1894 2.89
9. 1953 2.89
10. 2007 3.37

An energetic upper level low brought the first widespread precipitation of the rain season to Southern California October 9, with rain at the lower elevations and some snow in the local mountains. Rainfall amounts varied widely, ranging from a trace in some areas to over an inch in the mountains.

Downtown Los Angeles (USC) recorded only 0.04 inch for the storm, bringing the water year rainfall total to 0.13 inch, which is 0.31 inch below normal. Downtown Los Angeles has recorded only 2.76 inches of rain since January 1. This is one of the driest January 1 - October 20 in Los Angeles over the past 135 years! To get out of the bottom ten for calendar year rainfall Los Angeles needs about 3.5 inches of rain by December 31. Normal rainfall for November is 1.04 inches and for December is 2.33 inches.

For months I've been monitoring climate data and forecasts looking for something on which to base a 2013-14 Winter precipitation Outlook. Historically ENSO has played the major role in Southern California rain season weather, with El Nino conditions generally producing wetter weather and La Nina conditions generally drier. But ENSO conditions are currently Neutral and are expected to remain so through the end of the year.

Most climate models forecast slow warming of SSTs in the equatorial Pacific (NINO 3.4 region) over the next several months, but at this time of the year it would be very unusual to have substantial warming. The CPC/IRI ENSO Forecasts from IRI's October Quick Look indicate the probability of an El Nino developing before the end of the year is less than 20% -- and 20% seems high.

One computer model that at times has been forecasting above average precipitation in Southern California this Winter is the Climate Forecast System version 2 (CFSv2). The CFSv2 is fully coupled ocean-atmosphere-land-sea ice model used to forecast parameters such as sea surface temperature, temperature and precipitation rate. While skillful at predicting tropical SSTs, the CFSv2 generally performs very poorly when forecasting precipitation over land, so forecasts such as this earlier one for Dec-Jan-Feb must be viewed somewhat skeptically.

Another glass half-full observation is that the Madden-Julian Oscillation (MJO) has been relatively active this year and if this activity continues it provides recurring opportunities for enhanced U.S. West Coast precipitation. The downside is that it can result in periods of dry weather as well.

With the ocean and atmosphere neutral there's just not much on which to base a rain season forecast. As a result of the government shutdown the release of the official NOAA 2013-14 Winter Outlook has been delayed until November. The October CPC outlook is usually the basis of the initial official NOAA U.S. Winter Outlook. The U.S. Dec-Jan-Feb Precipitation Outlook, released October 17, calls for an equal chance of below average, average, or above average precipitation for all of California. We'll see!

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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.

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.

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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.

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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.

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!

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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.

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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.

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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!

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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.