UCLA Department of Atmospheric and Oceanic Sciences

Detailed Forecast

Today - Mostly cloudy day with showers developing mid-morning. Some showers may be briefly heavy. Decreasing chance of showers by tonight.

Tomorrow - Wednesday
Some early morning clouds possible; Otherwise, sunny day.

Outlook - Thursday through Saturday
Some clouds but mostly sunny Thursday/Friday. Sunny Saturday.

Temperature forecasts

Temperature outlook Thursday through Saturday

Lows
46 - 49 Thursday/Friday; Near 51 Saturday (8 - 11 Celsius)

Highs
63 - 65 Thursday/Friday; Near 69 Saturday (17 - 21 Celsius)

Synopsis
A new storm has entered the Southland today. Like a previous storm, pre-frontal showers developed more quickly than I expected(actually, I neglected to consider this yesterday). Pre-dawn showers occurred in some places(mainly east and south of L.A. County). Showers increased in areal coverage by late morning, but a lengthy period of steady rain in the lowlands isn't expected.

Atmospheric instability is sufficient for scattered thunderstorms, but so far, almost all these storms have been weak in intensity(rather small in size too). I opted to leave thunderstorms out of the campus forecast as I expect that to happen more inland areas or over the coastal waters(inland storms are "home grown" while the coastal waters storms should come ashore south of West L.A.).

Showers should diminish on the Westside by sunset(main frontal band should have passed by then). A secondary area of showers/thunderstorms(associated with the core of the upper level low pressure) should pass south of L.A. County tonight(area moving south down the coast but staying off-shore...landfall possible over San Diego County).

Storm totals in the lowlands should be quite variable due to the showery nature of the system. Rainfall in Santa Barbara County has been a quarter to half inch so far. The L.A. County coastal plain shouldn't get more than a half inch, and many areas probably won't receive more than a quarter inch(Inland Empire may turn out to the wettest area, based on computer model forecasts). Where thunderstorms occur, locally higher amounts are possible, but no prolonged thunderstorms are likely(limited water vapor and instability). Hence, any flooding problems should be much less than with the past storm.

Mountain snow should continue through the night and may persist in areas(desert facing slopes) well in day tomorrow. The snow level(currently near 5000 feet) should drop to near 2500 feet late tonight or early tomorrow. Several inches of snow should fall at resort level, but only a dusting is anticipated below 3000 feet.

Dry weather should return to the coastal plain tomorrow(gradual clearing for the mountains/deserts tomorrow). A weakening storm will bring showers to the northern third of the state late Thursday into Friday, but only some clouds are expected in southern California(modest warming trend through Friday).

By Saturday, all computer models forecast an off-shore flow. They disagree on its strength, but breezy weather is likely in the Santa Ana wind prone areas. Peak gusts Saturday night/Sunday could reach 45 mph in typically favored locales. Off-shore flow should weaken on Monday, but the off-shore flow may continue in some form through the middle of next week.

The predicted off-shore flow will provide warmer than normal weather this President's Day weekend. Widespread 70 degree weather is anticipated(coastal plain into the mid-70s). Isolated readings into the low 80s are possible by Sunday(Monday too).

While a number of longer range models show a rain threat around the 20th(plus or minus a day), fewer solutions show a significant storm(rainfall under a quarter inch). Only a few show a series of storms affecting the Southland in the last full week of February.

Weather forecasting and information provided by James Murakami, UCLA Department of Atmospheric and Oceanic Sciences

Issued: Tuesday, February 9, 2010 a 1:21:22 PM