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

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

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

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

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

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

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

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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.

Running in the rain and wind, and splashing through innumerable puddles, Markos Geneti set a new Los Angeles Marathon record in a time of 2:06:35. It was a remarkable performance, in adverse conditions. From 8:00 a.m. to 12:00 p.m. the Mt. Washington RAWS, near the start of the marathon, recorded 0.59 inches of rain; and the Beverly Hills RAWS near mile 17, recorded 1.27 inches. Periods of heavy rain were reported at Santa Monica Airport, near the finish line, through much of the race. According to a report in the Los Angeles Times sports blog, The Fabulous Forum, thousands of runners were evaluated for hypothermia and 25 runners were hospitalized.

Many rainfall records were set around the area Sunday, with some locations recording as much as one-third of a year's normal rainfall in 24 hours! In the early evening rainfall rates of over an inch an hour were recorded in Woodland Hills and Canoga Park. According to a NWS Storm Report, at 6:14 p.m. a flash flood was reported in Woodland Hills with "mud and debris flowing down the street" and "at least four to five vehicles stuck in flowing water."

Downtown Los Angeles (USC) recorded 2.42 inches of rain yesterday, breaking a record set in 1943. Santa Barbara Airport had its wettest day on record, recording 5.23 inches of rain. Here's an archived copy of the NWS Record Report for March 20, listing some of the rainfall records for the day.

Storm totals in excess of 3 inches have been common in Los Angeles, Ventura, Santa Barbara, and San Luis Obispo counties. Higher totals were recorded in many areas. As of 5:00 p.m. the NWS reported that Van Nuys had recorded 6.74 inches of rainfall, Northridge 6.08 inches, Newhall 7.20 inches, Santa Barbara Airport 6.27 inches, San Marcos Pass 10.72 inches, and Gibraltar Dam 11.73 inches. Here's an archived copy of a NWS report with some rainfall and snowfall amounts from around the area.

Downtown Los Angeles made up its rainfall deficit for the month of March and more, increasing its water year rainfall total to 18.55 inches, or about 123% of normal. This makes the 2010-2011 water year the wettest in Los Angeles during a La Nina over the last 60 years, surpassing the totals recorded during the strong La Ninas of 1955-56 (99% of normal) and 1973-74 (106% of normal), and weak La Ninas of 1967-68 (110%) and 2000-01 (118%).

Sunday's heavy rain appears to have had the earmarks of an atmospheric river event. NRL SSM/I IPW imagery (lower right) shows a pre-frontal band of IPW values of 35-40 kg/m2 impinging the coast, NEDIS blended TPW imagery showed a band of ~25 mm TPW extending some 4000 km to the longitude of Hawaii. A BUFKIT cross section based on 12z NAM data for VNY depicted a low level jet (LLJ) structure coinciding with the period of heaviest rainfall. Research by Dr. F. Martin Ralph, et. al., observed that in atmospheric rivers over the eastern Pacific, 75% of the water vapor transport below 500 mb takes place within the lowest 2.25 km and occurs with LLJ wind structure. In addition in cases where a LLJ is present, there was 50% greater precipitation efficiency.

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The strong cold front that swept through Southern California Christmas night resulted in 0.90 inch of rain at Downtown Los Angeles (USC), increasing December's rainfall total to 9.67 inches. This makes December 2010 the wettest December in 121 years (since 1889), and the second wettest December since recordkeeping began in 1877.

Rainfall totals from last night's fast moving front generally ranged from about 0.4 inch to 0.9 inch. Here's an archived copy of a Precipitation Summary from the NWS Los Angeles/Oxnard with some rainfall totals from around the area.

This morning's model runs continue to forecast more rain for Wednesday. The 12z NAM projects about 0.5 inch at LAX during the day Wednesday. The 09z SREF puts the probability of more than 0.25 inch of rain in the Los Angeles area at about 50% for the 24 hour period ending 4:00 p.m. Wednesday afternoon.

Depending on how much rain we get Wednesday, for the first six months of the 2010-11 water year (July 1 to December 31), the rainfall total for Downtown Los Angeles will likely rank as the fourth or fifth wettest in the 133 years that records have been kept.

In the medium range outlook, the 12z GFS and 12z ECMWF differ in how they handle an upper level low that they forecast to develop off the California coast New Year's morning. The 12z GFS is quite wet New Year's weekend, but it's too early to put much credence in that forecast. We'll see!

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After producing phenomenal rainfall totals in Southern California and snowfall totals in the higher elevations of the Sierra, the Pacific low and trough responsible for days and days of wet weather has finally moved east.

Some stations recorded more rain in the last 7 days that would normally be recorded over an entire year. Precipitation amounts over 10 inches were common, and several stations recorded over 20 inches. Tanbark, in the San Gabriel Mountains recorded 24.7 inches, NF Matilija in the Ventura Mountains recorded 24.09 inches, and Lytle Creek in the San Bernardino Mountains recorded an astonishing 26.35 inches!

Here's are snapshots of provisional 7-day rainfall totals in Ventura County and 7-day rainfall totals in Los Angeles County from the Ventura County Watershed Protection District ALERT Map Viewer; and a snapshot of provisional 7-day rainfall totals from the NWS San Diego's Experimental Rainfall Summary Display. And here are archived copies of NWS precipitation summaries with preliminary rainfall totals from the NWS Los Angeles/Oxnard and NWS San Diego offices.

The remarkable amount of rainfall makes December 2010 one of the wettest on record in Southern California. According to preliminary NWS data Downtown Los Angeles (USC) has recorded 8.52 inches of rain so far this December. This ranks it as the third wettest December in Los Angeles since recordkeeping began in 1877, exceeded only by December 1889 (15.8 inches) and December 2004 (8.77 inches). With additional rain a possibility, December 2010 only needs 0.25 inch to surpass 2004. For more detailed info see "A Look at the Record-Breaking Week of Rainfall" a PDF from the NWS Los Angeles/Oxnard.

The Sierra recorded gargantuan snowfall totals, with some of the largest being in the Southern Sierra. In the last week the snow sensor at Farewell Gap recorded 22.6 inches snow water equivalent, which roughly translates to 18 feet of snow. This morning California Cooperative Snow Surveys reports the Southern Section Sierra snowpack at 287% of normal, and the snowpack overall in the Sierra at 207%! Mammoth Mountain reports 167 inches of snow so far this December, a new record for the period 1968 to date, obliterating the records set in 1971 (139.8 inches) and 2002 (134.4 inches).

As of yesterday Downtown Los Angeles (USC) rainfall was a whopping 6.88 inches above normal for the water year. That puts us way, way ahead of what is typical for a La Nina influenced rain season -- at least for a couple of months.

Update December 24, 2010. Looks like there will be two opportunities before the end of December for Downtown Los Angeles (USC) to increase its rainfall total for the month and become the second wettest December since recordkeeping began in 1877. The first chance is Saturday night. For the 24 hour period ending 10:00 a.m. Sunday, the 09z SREF puts the probability of more than 0.25 inch of precipitation in the Los Angeles area at about 70%. The WRF ensembles precipitation forecast for LAX for Saturday night ranges from a low of about 0.25 inch to a high of about 0.7 inch. The 18z GFS says the second opportunity will be Wednesday, and forecasts a little under an inch of rain at LAX. We'll see!

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

October was an unusually wet month in coastal Southern California. Many areas recorded more than an inch above normal rainfall, and some as much as 3 inches above normal. In a month where around 0.5 inch is considered normal, some areas received several times the normal amount of rainfall.

Most of October's rain resulted from two energetic upper lows, and a relatively strong trough/front that swept through the area October 30th. The front produced a new precipitation record for the date of 1.09 inches at Santa Barbara Airport Here's an archived NWS Public Information Statement with some rainfall totals for that storm.

Last week, an approaching Pacific trough pumped up a thick high pressure ridge over California, sending temperatures soaring and breaking temperature records across the area. November 3rd Long Beach Airport set a new high temperature record for the date of 100°F, and Downtown Los Angeles set a new record of 97°F. November 4th temps were once again in high 90s and several stations broke or tied high temperature records. Here are archived copies of the NWS Record Event reports for November 3 and November 4.

The southern part of the Pacific trough that produced our record high temps cut-off into a small upper low as it approached the coast, and moved onshore north of the Los Angeles basin on Saturday. The remainder of the trough and its associated front moved through the area Sunday evening into Monday. The front held together a little better than expected, and rainfall totals in the Los Angeles basin and valleys generally ranged from about 0.10 inch to 0.30 inch. Here's an archived NWS Public Information Statement with some rainfall totals from around the area..

The latest round of rainfall leaves many areas of Southern California way ahead on rainfall totals for the water year. Downtown Los Angeles (USC) missed out on a couple of the systems, and as of close of business yesterday has recorded 1.10 inch for the water year, which is only 0.06 inch above normal. By comparison, Los Angeles Airport is 0.85 inch above normal, and Camarillo/Oxnard is 0.97 inch above normal. This headstart on the rain season should help keep our rainfall totals a little closer to normal as our La Nina influenced rain season continues.

Speaking of La Nina, the September/October value of the Multivariate ENSO Index (MEI) increased slightly by 0.079 sigma, ending the record plunge from El Nino conditions earlier this year. In the past 30 days there was some decrease in the magnitude of negative SST anomalies in the east-central equatorial Pacific, but subsurface temperatures remain quite cool. Computer models are split on whether Nino 3.4 SST anomalies will continue to decline in magnitude during the Northern Hemisphere winter, but nearly all models indicate decreasing anomalies in early 2011. We'll see!

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