Monsoonal flow that began last Thursday has resulted in numerous thunderstorms in the mountains and deserts of Southern California, with flash flooding and debris flows reported in several locations.

Areas in or near recently burned terrain are particularly susceptible, and flash floods and debris flows appear to have originated in the 2007 Oak Fire burn area in the eastern Sierra, and the still burning Piute Fire burn area near Lake Isabella.

This sequence of three GOES-WEST VIS/IR satellite images from NRL's NEXSAT web site shows the explosive development of a convective cell north of Mt. Whitney on Saturday afternoon. This appears to be the thunderstorm that produced the heavy rain in the area burned by the Oak Fire, and resulted in the Oak Creek debris flow near Independence. Here's an AVI loop, generated on the NEXSAT web site, for the period 3:00 p.m to 6:00 p.m. PDT on Saturday.

A particularly large thunderstorm cell/complex developed in the Sierra Nevada south of Mt. Whitney midday Saturday and drifted south down the Kern River drainage over the course of the afternoon. At about 2:45 p.m. the cell/complex was centered near the confluence of the Little Kern River and N.F. Kern River and measured about 44 miles in diameter. Here's a Google Earth image of the cell/complex with a 250m resolution True Color Aqua cloud layer imported from the MODIS Rapid Response System.

This GOES-East/West Precipitable Water composite from 9:00 this morning indicates precipitable water values as high as 1.6" in some areas of Southern California, and the possibility of more mountain and desert thunderstorms continues today.

Update July 25, 2008. The large cell/complex that developed south of Mt. Whitney on Saturday, July 12, and drifted south down the Kern River drainage appears to have produced the flash flooding and debris flows on Erskine Creek and other creeks in the Lake Isabella area late Saturday afternoon. This cell/complex can also be seen in sequence of three GOES-WEST VIS/IR satellite images and the AVI loop previously referenced.

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Temperatures today at Los Angeles Pierce College in Woodland Hills appear to be running about a degree hotter than yesterday, when a new record high for the date of 109°F was recorded at the campus weather station.

A BUFKIT analysis of 12z data for Van Nuys shows temps peaking today at about 107°F, followed by a slow cooling trend into next week, with high temps dropping down into the high eighties. In this graph of temperatures, the red line is the 2-meter temperature and the blue line is the surface "skin" temperature.

Equatorial Pacific SSTs continue the transition to neutral conditions. This TAO section plot of 5-day Depth Average Temperature clearly shows the change in state with a marked increase in sub-surface temperatures, particularly in the far eastern and western equatorial Pacific.

It looks like Downtown Los Angeles (USC) will end the July 1, 2007 to June 30, 2008 water year with 13.53 inches of rain recorded. This is 91% of the 1921-2006 average of 14.87 inches.

Update Monday, June 23, 2008. On Friday, Los Angeles Pierce College in Woodland Hills eventually reached a record-setting high of 111°F! Here is an archived copy of a NWS Los Angeles/Oxnard Record Event Report listing record highs from around the area for Friday, June 20.

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More Wet Weather Possible Today and Tomorrow.

The unseasonably energetic upper level low that replaced our unseasonably strong high has resulted in dramatic weather in Southern California, including heavy rain, hail, thunderstorms, lightning, and even a pair of tornadoes near March Air Force base. This UCAR regional radar image from yesterday at 5:00 p.m. shows the intense cell that likely spawned the tornadoes.

In Los Angeles County, very heavy rain was recorded in the San Gabriel Valley. According to a NWS Public Information Statement, as of 7:00 p.m. yesterday, 2.29" was recorded at Santa Fe Dam, 1.51" at Whitter Narrows, and 1.42" at the San Gabriel River at Valley. Yesterday, Downtown Los Angeles (USC) recorded 0.05 inch of rain, bringing the water year total to 13.47 inches.

Intellicast radar shows showers continuing in Southern California this morning. The upper level low is forecast to remain over Southern California into Sunday, and BUFKIT analysis of 12z NAM data for several Southern California stations (VNY, LAX, ONT) suggest on and off rain showers may occur through Sunday morning. As long as the cut-off upper low remains over the area there is also the possibility of an isolated heavy shower or thunderstorm developing. We'll see!

Update Sunday, May 26, 2008. Here is an archived copy of a NWS Public Information Statement with rainfall totals for this event through 6:00 p.m. Saturday.

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Chance of a Shower Next Weekend?

An unseasonably strong and extended Pacific jetstream has resulted in a very high amplitude high pressure ridge over the West Coast with record and near record temperatures seen from Seattle to San Diego.

Yesterday, Woodland Hills set a new high temperature record for the date of 101°F. Record high temperatures were also recorded at Ojai, Sandberg, Santa Ana, El Cajon, Red Bluff, Redding, Sacramento, Stockton, Modesto, San Jose, Eureka and several other stations in California. Triple digit highs were recorded across much of the interior of the state.

It's hot again today, and will be hot again tomorrow, but the GFS, ECMWF and other guidance is suggesting that as the extended Pacific jet collapses, the west coast ridge will retrograde off the coast and be replaced by a trough by Memorial Day Weekend. This would result in cooler weather in California, and even the possibility of showers in some areas, such as the Sierra and our local mountains. We'll see!

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In it's April 30 ENSO Wrap-Up, the Australian Bureau of Meteorology characterizes Pacific climate patterns as being generally neutral, "with the majority of indicators returning to near-normal levels." The April 28 ENSO Update from the CPC suggests that La Niña will continue through May-July 2008, but many of the factors discussed indicate general weakening of the cold ENSO episode.

We've had only a smattering of rain at Downtown Los Angeles since 0.46 inch was recorded back on February 24. A miniscule 0.01 inch was recorded on March 15, and 0.04 inch on April 2. These NOAA/NWS AHPS Precipitation Analyses map the 60 day Departure from Normal Precipitation and 60 day Percent of Normal Precipitation for the southwestern U.S., as of April 30, 2008.

As of May 1, the water year rainfall total for Downtown Los Angeles (USC) stands at 13.42 inches. This is 90% of the 1921-2006 average of 14.87 inches. According to the 1921-2006 dataset, the average amount of precipitation in May and June has been 0.3 inch and 0.1 inch, respectively. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Normal precipitation. We'll see!

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A blustery Spring storm is expected to produce measurable rain over much of Southern California tomorrow. As has often been the case this year, the 12z NAM and 12z GFS are at odds, with the NAM generating less than 0.25 inch at Los Angeles, and the GFS more than 0.5 inch.

Today's NWS Precipitation Outlooks for Southern California indicate normal precipitation in the 6-10 day period and below normal for the 8-14 day period. We'll see!

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A weak cold front held together a little better than expected, producing a few showers in the Los Angeles area early Sunday morning. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 5:00 p.m. No measurable rain was recorded at Downtown Los Angeles (USC- KCQT).

Only 0.01 inch of rain was recorded at Downtown Los Angeles (USC- KCQT) the entire month of March, pulling the water year rainfall total more than a 0.5 inch below normal for the first time this rain season. It looks like there's a pretty good chance of some rain Wednesday. We'll see!

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Weather conditions were tough for the Amgen Tour of California cyclists cranking over Mill Creek Summit yesterday. The Mill Creek RAWS recorded an average temperature of 35°F, with winds of 25 mph, gusting to 40 mph, at about the time the peloton cleared the summit. The Clear Creek RAWS, where riders turned right onto Angeles Crest Highway, recorded about 0.20 inch of rain during the afternoon, with the temperature hovering at around 40°F.

As bad as it was for the tour cyclists, the system was generally not as wet as expected -- particularly in the Los Angeles County mountains, where precipitation amounts ranged from about 0.25 inch to about 1.0 inch. Similar rainfall amounts were recorded in the Los Angeles basin and valleys.

Downtown Los Angeles (USC- KCQT) recorded 0.07 inches of rain Saturday, and 0.46 inches Sunday, bringing the water year total (since July 1) to 13.37 inches, which is about 3.1 inches above normal for the water year to date.

Since mid-week last week some Sierra snow sensors have recorded as much as 8 or 9 inches snow water equivalent of precipitation -- the rough equivalent of 6 or 7 feet of snow. Today's Statewide Summary of Snow Water Equivalents, provided by the California Cooperative Snow Surveys, reports the Sierra snowpack at 119% of normal for the date and 101% of the average April 1 seasonal total.

It looks like most of the west coast weather action will be shifting to the Pacific Northwest for the next week or so. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation. We'll see!

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Rapidly intensifying Pacific low pressure system approaching the west coast looks very impressive on satellite images this afternoon, with strong upper and low level jet dynamics, a good moisture feed, and a classic baroclinic leaf.

The system is forecast to be filling as it moves onshore, but a very strong jet max moving through the base of the trough should keep the dynamics interesting. In any case, significant rain is expected throughout much of California over the weekend, with heavy snow in the Sierra.

Southern California is forecast to be on the southern margin of the action, however in keeping with the wet trend this rain season, the 18z GFS is forecasting about 1.5 inches of rain at Los Angeles from midday Saturday through Sunday afternoon, and the 18z NAM about 1.0 inch. A moderately strong mid-level southerly to southwesterly inflow should increase precipitation amounts in favored foothills and mountain locations.

Precipitation totals resulting from the passage of the second trough yesterday afternoon into this morning have ranged from about 0.25 to 0.75 inch in the Los Angeles area, with up to about 1.0 inch recorded at some locations. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. Isolated showers have continued to pop up around the Los Angeles area much of the day, but are forecast to be ending in most areas this evening.

Downtown Los Angeles (USC- KCQT) recorded 0.19 inches of rain Thursday, bringing the water year total (since July 1) to 12.84 inches. We're still at a deficit for the month of February, but remain above normal for the water year to date. Much of the February deficit may be erased by Monday. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation.

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Precipitation totals from the first of a series of shortwaves associated with a extended Pacific jetstream produced rainfall amounts ranging from about 0.1 to 0.25 inch in the Los Angeles area yesterday, with up to about 0.5 inch recorded in some mountain locations.

Downtown Los Angeles (USC- KCQT) recorded 0.14 inches of rain Wednesday, bringing the water year total (since July 1) to 12.27 inches -- still about 2.5 inches above normal for the date. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. yesterday afternoon.

There were a few sprinkles this morning, and Intellicast composite radar shows some shower activity around the area at 12:30 p.m. this afternoon. More general rain is expected to develop this afternoon or evening. Today's 12z NAM projects about 0.6 inch at Los Angeles between now and mid-morning Friday. Over that same period, a BUFKIT analysis of 12z NAM data for Van Nuys projects about 0.75 inch, but an analysis of 12z GFS data generates only about 0.25 inch.

A third system is forecast for the Saturday afternoon into Sunday timeframe and is expected to produce similar amounts of precipitation. However, the upper level flow will be transitioning to a more amplified pattern, so the computer models may have some difficulty with the forecast. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Below Normal precipitation.

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Today's trough was supposed to be an inside slider that stirred up some strong winds, and perhaps some drizzle. A more westward position of the upper low than forecast by yesterday's 18z GFS and NAM, has resulted in a more vigorous system that has produced rain in several areas of the Southland and snow in the mountains.

As of 11:00 a.m. the California Nevada River Forecast Center Los Angeles Area Precipitation Map shows 24 hour precipitation amounts ranging from 0.1 to 0.2 inch, generally south of the Los Angeles basin.

The last few runs of the GFS have been indicating a transition back to a wetter pattern around mid-week of next week, when a strong Pacific jet and a series of shortwave troughs are forecast to target the west coast. It appears that there is the possibility of a significant precipitation event in California, but it's too early to say where, when and how much rain may occur. We'll have to see how things develop over the next few days!

Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Above Normal precipitation.

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Sunday's storm added more rain to Southern California's unexpectedly wet water year totals, and more snow to the Sierra snowpack. This rain season western storms have reduced drought classifications by as much as three steps in some areas of California and four in Arizona.

As of February 4, Downtown Los Angeles (USC- KCQT) has recorded 12.13 inches of rain since July 1-- about 4.5 inches above normal for the date. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals for Sunday's storm.

Sierra snow course measurements for February 1 are coming in and manual measurements are confirming what automatic snow sensors have already reported -- that the Sierra snowpack is well above normal for the date.

Will the wet western weather continue? The GFS and ECMWF medium range models, and NCEP and PSD ensembles are forecasting a generally quiescent, rain free period for Southern California over the next several days, and into the extended period. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Below Normal precipitation.

However, there are suggestions (see Atmospheric Insights) that sometime around February 15-20, the currently active MJO may more or less phase with the GWO, and amplify La Nina to produce a energetic, extended Pacific jet and west coast trough, similar to what occurred around January 3, 2008. We'll see!

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