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.

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.

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.

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.

If current precipitation forecasts and outlooks validate, December 2010 could become one of the wettest on record in California, and at the higher elevations of the Sierra, one of the most snowy. This morning's 5-day precipitation forecast from the Hydrometeorological Prediction Center, for the 5-day period ending early Wednesday morning, indicates up to 7.9 inches of precipitation locally, and 14.7 inches (water equivalent) in the Sierra. And additional precipitation is forecast beyond the 5 day period.

A large Pacific low working in concert with a low west of Hawaii has established a tropical connection, and is pumping copious amounts of moisture into California. This tropical moisture conveyor belt scenario is currently forecast to continue into next week. Late Sunday, shortwave impulses dig down into the low and elongate it southwestward, creating a large longwave trough. This northern part of this trough is forecast to evolve into another large upper and surface low in the northeastern Pacific. The southern part of the trough is forecast to develop a surface low and front that moves into Southern California Tuesday into Wednesday.

In the short term, BUFKIT analysis of WRF ensemble data for Van Nuys shows precipitation totals through early Sunday morning ranging from about 1.0 inch up to about 3.5 inches. Analysis of 12z NAM data for Van Nuys produces around 1.8 inches through early Sunday morning and nearly 5 inches through early Monday morning. The 09z SREF pegs the probability of more than 1.0 inch of precipitation in Los Angeles area at around 70%. Precipitable water values of over 1.0 inch, high relative humidity, and a strong south to southwesterly inflow of over 30 knots should produce significantly enhanced precipitation on favored slopes -- generally those with a south to southwest aspect.

It's a little early to put much credence in forecasts for next week, other than more rain appears likely. The 06z GFS produced astronomic precipitation totals mid-week -- several inches more than either yesterday afternoon's 00z run (2.75 inches), or this morning's 12z run (4.6 inches). We'll see!

As of yesterday Downtown Los Angeles (USC) rainfall was 0.91 inch below normal for the water year, and much of Southern California was falling behind in the rainfall department. It looks like by next week we'll be ahead of the La Nina game again, perhaps way ahead.

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

Thanks to October's unusual amount of rainfall, precipitation totals for many areas of Southern California remain near or above normal for the 2010-11 water year. But November has been relatively dry, and Downtown Los Angeles (USC) is now about 0.30 inch below normal for the month, and for the water year. That's expected to change over the weekend.

A series of impulses on the downstream side of a high amplitude upper ridge is forecast to amplify a trough and generate an energetic upper low along the coast of the western U.S. tonight.

The 00z NAM/WRF shows a strong front moving down the coast and through Southern California on Saturday, a second impulse on Sunday, and possibly a third on Monday.

BUFKIT analysis of this evening's 00z NAM data for Van Nuys project rainfall totals of about an inch over the 24 hr. period ending Saturday at 4:00 p.m., and then another third of an inch or so Sunday. The 00z GFS isn't as generous with the rainfall amounts, generating about 0.5 inch on Saturday and 0.3 inch on Sunday, but appears too fast when compared to current satellite and radar images.

SREF means & spreads suggest amounts across the area should generally range from about 0.5 inch to 1.25 inches, with more expected in the mountains. We'll see!

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