UCLA Weather

from the Department of Atmospheric and Oceanic Sciences.

Friday - 3:13pm



High - 75°

Low - 63°

Today: Sunny day. Clear evening.

Five Day Forecast

Latest Average Hourly Temperatures

The marine layer deepened slightly last night, but it dropped back to about the same depth as yesterday morning early today. That was surprising (to me) in that the on-shore flow strengthened overnight (not just for a few hours). What triggered the lowering of the marine layer wasn't clear to me. More perplexing (again, for me), was the decreased, areal coverage of low clouds early today (much less from L.A. County southward). The coastal eddy appeared farther off the coast, which may have had an influence in less low clouds. However, I've seen other occasions where an eddy well off the coast still promoted widespread, low clouds. Once again, the complexities of the marine layer have baffled me.

As stated yesterday, only minor day to day changes are forecast in the wind flow pattern affecting southern California. Slight weakening in the on-shore flow is expected tomorrow. Some computer model forecasts continue to show a marginal, surface off-shore flow early tomorrow. However, the upper air support for relevant warming appears lacking (in the model forecasts). Hence, almost no temperature changes in daytime readings (today versus tomorrow) may occur near the coast. Well inland areas should be modestly warmer tomorrow (likely widespread 90 degree weather in the valleys), but slight cooling should follow on Sunday (another reversal to stronger on-shore flow). Another warming cycle is expected early next week (Monday or Tuesday), but that too, should be modest at best (midweek temperatures not too different from what's expected tomorrow).

The predicted, areal coverage of marine layer, low clouds remains a question mark. Unless some dry air entrainment into the low cloud field occurs, early morning low clouds should remain a daily ,weather staple by the coast. Clouds shouldn't extend far inland nor persist long through the morning hours (excepting some beaches though). An upper air trough passing by to our north should increase the on-shore flow enough to promote more widespread low clouds Monday morning (coastal plain and perhaps some valleys). Less coverage should follow on Tuesday (possibly minimal coverage second half of the week).

Upper level high pressure is forecast to be situated over the state late next week. It should persist going into the first days of October. Warmer than normal weather is expected for most areas, but it's becoming less clear if a well defined, off-shore flow will occur. Some model solutions are trending away from that scenario (could be feeble like what's expected tomorrow). Warmer than normal weather is likely for a few days, at least. However, it's unclear whether widespread 90 degree weather will occur in the coastal plain for a couple days. There are some model forecasts showing the current, minor ups and downs in daytime temperature will be the rule for the remainder of the month.

UCLA Forecasts and analyses are written by James Murakami

– posted: 2018-09-21

Data and technology is provided by UCLA's Department of Atmospheric and Oceanic Sciences

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