Weather Synopsis – March 26, 2024

James Murakami

Tue26th64/52Some lingering, morning low clouds, but mostly sunny day. Mostly clear evening.
Wed27th66/53Chance of some early morning low clouds; Otherwise, mostly sunny day with some high clouds. Some high clouds in the evening.
Thu28th65/53Chance of morning low clouds; Otherwise, mostly sunny day with variable high clouds. Becoming mostly cloudy in the evening.
Fri29th62/54Possible, partial afternoon clearing; Otherwise, mostly cloudy through the evening. Chance of light showers in the evening.
Sat30th59/51Periods of rain, heavy at times; Breezy at times. Showers likely in the evening.


Low level, on-shore flow prevailed today in southern California. Along with a coastal eddy circulation, marine layer clouds were abundant in most areas west of the mountains (most persistent in San Diego County where some areas of drizzle/light rain fell early). High pressure aloft will build into the region tomorrow. It’ll help weaken the on-shore flow and should make the marine layer shallower. However, the computer models aren’t predicting any defined, off-shore flow (some northerly winds in some areas but not of lengthy duration). The marine layer may remain well defined, and low clouds may occur in the coastal plain in the early morning hours (might stay out of most coastal valleys but not certain). Any warming tomorrow (compared with today) should be minor in most areas (modest warming where northerly winds reach the ground).

The aforementioned high pressure will weaken and slide off to the southeast on Thursday. On-shore flow should pick up in strength again. An approaching, large trough of low pressure will also bring varying amounts of high clouds into the Southland (wet weather expected over much of northern California and briefly possible as far south as western Santa Barbara County). The weather should look gloomier down here on Friday as the trough become more established off the northern California coast. Though still a few days away, the vast majority of models have been projecting a significant, spring storm for the state (actually comprised of multiple “waves”…starting in the northwest corner of California tomorrow). Rain is likely to reach San Luis Obispo/Santa Barbara Counties by Friday evening. There is even a chance that some light showers will develop in L.A. County by late evening. It’s almost a certainty that it will be a wet weekend in southern California (not necessarily continuously throughout). Much cooler than normal weather is a virtual certainty (origins in the Gulf of Alaska). However, details of the expected wet weather remain to be hammered out.

The upcoming storm system will be a semi-“cut-off” low pressure (hasn’t developed yet). As with may such circulations, numerical models infrequently handle the predicted course of storm poorly. That is, predicted duration, strength, and areal coverage may not necessarily verify as the models predict. As it stands right now, an accompanying cold front should pass through L.A. County sometime Saturday morning. A period of very heavy rain should occur in most areas. Numerous showers are expected to follow for the remainder of the day and evening. Some areas may be more consistently wet than other areas…especially near/adjacent to coastal facing foothills and mountains. The weather should also be breezy for a time (interior sections starting as early as Thursday when on-shore flow picks up substantially).

Showery weather, including some thunderstorms are expected on Sunday (some chance of isolated thunderstorms on Saturday but more uncertain). Where the greatest activity (i.e. heavy intensity rain showers) occurs will depend on course the aforementioned, “cut-off” low pressure takes on Easter. There is a chance that most or all of those heavy showers will fall to the south and east of L.A. County (“cut-off” center taking a more southern route). What showers occur in L.A. County may occur just in the morning hours (possibly early morning). It’s still too early to say with any real confidence what the weather will be like that day. At the least, there should be much less wind compared with Saturday.

Except for possible instability showers Monday afternoon (mostly over/adjacent to the mountains), that day should be a mostly dry day in the lowlands. The “cut-off” low pressure should be on its way out of the Southland by late Monday afternoon. Storm totals for the period beginning late Friday through Monday should range in the 2 to 3.5 inch range in the lowlands away from the mountains (impressive for spring, let alone a winter storm). Twice as much rain could fall in areas up against coastal facing mountain slopes. Snowfall at the local resorts (~ 6000 feet) may be in the one to two feet range (snow levels mostly at or above 6000 feet until late Saturday…falling to 5000 feet by Sunday). These numbers assume the model consensus holds up. If the “cut-off” center stays too far off the coast or makes landfall well south of L.A., totals should be much lower (maybe less than an inch rain in the L.A. Basin).

Dry and warmer weather should return for Tuesday. If some models are right predicting a marginal, off-shore flow, slightly warmer than normal weather can be expected (Tuesday/Wednesday next week). More seasonal weather should prevail for the remainder of next week (possible return of marine layer clouds in the coastal plain). Some model solutions show a rain threat by the subsequent weekend (another weekend?!), but that’s far from certain at this time.

Next issued forecast/synopsis should be on Thursday, 28 March.