UCLA Department of Atmospheric and Oceanic Sciences

Detailed Forecast

Today - Mostly sunny day with scattered high clouds. Increasing clouds tonight leading to a slight chance of light showers after midnight.

Tomorrow - Saturday
Some morning clouds but becoming mostly sunny; chance of pre-dawn, light showers.

Outlook - Sunday through Tuesday
Sunny days.

Temperature forecasts

Temperature outlook Sunday through Tuesday

Lows
49 - 51 Sunday/Monday; Near 55 Tuesday (9 - 13 Celsius)

Highs
Near 67 Sunday; 72 - 75 Monday/Tuesday (19 - 24 Celsius)

Synopsis
On-shore flow has returned, and that's promoting cooler weather today. However, the cooling hasn't been as much (most areas) as I had expected. The weaker than anticipated on-shore flow this morning contributed, but I still thought moderate cooling would occur. Well, at least on campus, the high appears to have peaked at 71 degrees(12:16 PM)...temperatures back to the upper 60s as of this writing. It should be cooler tomorrow in most areas in the wake of a passing cold front.

The weak on-shore flow this morning resulted in areas of dense fog at/near the coast from about Venice Beach southward(cleared fairly quickly)...something I neglected to mention yesterday. Low clouds should be on the increase tonight as a cold front approaches. Still, no widespread overcast is likely in L.A. County before midnight. Skies should clear out by sunrise tomorrow in the County(clearing from west to east).

The southern end of a storm affecting northern California today will be pretty weak. Scattered showers are probable down to about Point Conception overnight. The north facing slopes of the Tehachapi Mountains should also receive showers(rain except for highest peaks). Elsewhere in the Southland, the chances for showers don't look that great. Because the cold front should be relatively high in water vapor content, I left the risk at "chance" for the pre-dawn hours(actual threat in the L.A. basin should last no longer than half an hour). Measurable rain is very unlikely in the County.

Although the computer models predict a marginal off-shore flow on Sunday, another storm is forecast to pass by well to our north. The passage to the north should prevent much warming on Sunday. At best inland areas may warm back to near normal(only minor warming expected near the coast).

A more noticeable warming should start on Monday. By then a definitive off-shore flow should be in place. Just how warm it gets next week and when that occurs is a little uncertain. Most past model runs showed Wednesday to be the warmest day next week. However, a number of models today show a weak upper air disturbance that could limit warming on Wednesday(warmer than normal but not likely with widespread 80 degree weather). If some model solutions are right, Thanksgiving Day will be the warmest day(widespread 80 degree weather possible even near the immediate coast). Cooler weather would follow, but cooling might be minor for the remainder of the holiday period(at least, based on some model scenarios...others show more robust cooling to below normal temperatures).

That disturbance I mentioned may also help trigger a moderately strong Santa Ana wind event around the middle of next week. Wind gusts could exceed 60 mph in the mountains. At this point, I'm leaning toward less wind, but it should nonetheless be breezy in the Santa Ana wind prone areas in the first half of next week.

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

Issued: Friday, November 20, 2009 a 1:22:28 PM