Weather Synopsis – March 5, 2024

James Murakami

Tue5th63/50Some clouds but mostly sunny day. Becoming partly cloudy in the evening.
Wed6th60/48Partly cloudy early but becoming mostly cloudy; Rain becoming likely by late afternoon into early evening. Ran may be briefly heavy. Rain tapering to a chance of showers late evening.
Thu7th63/49Some clouds but mostly sunny morning; Partly cloudy afternoon with a slight chance of brief showers. Becoming mostly clear in the evening.
Fri8th67/51Sunny day. Mostly clear evening.
Sat9th67/51Mostly sunny day with some high clouds. Some high clouds in the evening.


Weak high pressure aloft exists over southern California today. No low level, off-shore flow accompanies this high pressure. So, marine layer clouds are prevalent across many areas west of the mountains (scattered clouds to partly cloudy though mostly clear along and off the coast). The marine layer has also limited daytime warming despite the high pressure aloft and weaker on-shore flow (compared with yesterday).

A Pacific trough of low pressure is approaching the state from the west. All the computer models predict widespread, wet weather over southern California (main body of the storm aimed at the Southland…little wet weather expected over northern California this time around). Depending on whether an organized marine layer develops overnight, there is a chance for some areas of drizzle/light rain tomorrow morning (leaning against that with this campus forecast but confidence not the greatest). Some models favor showers reaching L.A. County early tomorrow afternoon. Other model solutions favor late in the afternoon. In any case, wet weather across L.A. County is expected by sunset. If some model solutions are right, a period of moderate to heavy intensity rain will occur (usually reliable ECMWF model in this camp). Isolated thunderstorms can’t be ruled out with this scenario (not included in the campus forecast though). Once the accompanying cold front passes by, the steady rain should taper off to scattered showers (probably mid-evening on the Westside…front moving from west to east).

Other than lingering, isolated showers, most of L.A. County shouldn’t see wet weather in the overnight hours (Wednesday into Thursday). Though there will be plenty of residual water vapor, it may start out mostly clear in many areas Thursday morning (daylight hours). Gradually, some low level, atmospheric instability should promote scattered clouds to perhaps partly cloudy weather (more so in the afternoon). A number of model solutions show a secondary, upper air disturbance passing near or over the Southland late Thursday afternoon. Predicted atmospheric instability should be marginal, but some showers and even brief-lived thunderstorms could occur, especially over and adjacent to the mountains. Thus, I wrote in a slight chance for a brief shower in the campus area for late Thursday afternoon. Conditions for showers should rapidly disappear by sunset (upper air disturbance should have exited L.A. Basin by that time).

Storm totals in the lowlands away from the mountains should range in the quarter to three quarter of an inch range (similar to the most recent storm a few days ago although there were exceptions). Snow levels should fall to 5000 feet late Wednesday evening. It could fall a little more by early Thursday. With the bulk of the precipitation expected with the cold front, little snow accumulation should occur below 5000 feet. At resort level a few to several inches of snow is likely (well under a foot, based on storm a few days ago).

Dry, mostly sunny weather should prevail on Friday. Some model forecasts indicate a marginal, off-shore flow for that day. There is a chance for gusty, northerly winds in Santa Ana wind prone areas, especially at higher elevation (peak gusts 50 mph at higher elevations). However, this is far from certain, and it should be short-lived in duration (wind slacking off in the afternoon). Temperatures could get slightly above normal levels if the marginal off-shore flow develops, but for this forecast, I kept things a tad cooler.

Most models show additional storms passing through northern California over the weekend and early next week (every 24 to 36 hours). All are forecast to be fairly minor with regard to precipitation. Based on the current model consensus, these storms should largely bypass southern California (some scenarios include minor, brief showers San Luis Obispo County and north facing Tehachapi Mountains). The predicted high pressure, however, shouldn’t be strong enough to promote totally clear skies nor any significant warming trend (at least through early next week). The outlook gets murkier late next week. The vast majority of models favor high pressure building over or near the state by the second half of next week. Depending on which scenario verifies, we could see several days of warm weather in the Southland. Or, there could be breezy, somewhat cool, Santa Ana winds (temperatures mostly near normal). There is even a scenario (remote chance at this point) of a nearby, “cut-off” low pressure that could promote some mountain showers…partly cloudy west of the mountains and slightly cooler than normal temperatures). At this point, there is no clear favorite (coin toss forecast though statistically speaking, the odds should favor sunny and warm).

Next issued forecast/synopsis should be on Thursday, 7 March.