Weather Synopsis – March 28, 2024

James Murakami

Thu28th64/51Mostly sunny morning; Variable afternoon high clouds. Partly cloudy evening.
Fri29th62/53Partly cloudy morning; Partly to mostly cloudy afternoon. Mostly cloudy evening with a chance of light showers.
Sat30th59/50Overnight rain, heavy at times and breezy; Partly to mostly cloudy day with a good chance of occasional showers. Partly to mostly cloudy evening with a good chance of showers.
Sun31st60/49Partly to mostly cloudy through the evening. A chance of showers and a slight chance of a thunderstorm during the day. Deceasing chance of showers in the evening.
Mon1st April65/50Some morning clouds possible but mostly sunny day. Mostly clear evening.


An upper level trough occupies the waters off the West Coast (center west of Washington state early this afternoon). A disturbance passing through the large scale trough brought some modest precipitation as far south as western Santa Barbara (yesterday and overnight). The trough also promoted the return of a healthy on-shore flow in southern California (reason for brisk, afternoon winds in the interior as well as along most of the coast).

All the computer models predict that the low pressure west of Washington will reform farther south tomorrow (west of northern California). This semi-“cut-off” low pressure will then travel down the West Coast (center staying over the ocean but eventually moving inland south of the border early next week). Wet weather associated with this low pressure will bring widespread wet weather to the Southland (starting San Luis Obispo County tomorrow afternoon). The most concentrated rain in L.A. County should occur with a cold front in the overnight hours early Saturday (short duration period of heavy to intense rain). It should also be breezy with this portion of the storm. The remainder of the weekend should be showery west of the mountains. Some lowland areas should get little further rain while other areas experience occasionally, brief-lived downpours. Isolated thunderstorms may occur on Saturday, but activity may become more numerous on Sunday. Showers should diminish greatly by Sunday evening (exiting most or all of L.A. County). Some chance for renewed, instability showers may occur Monday afternoon, but this should be mostly over/adjacent to the higher mountains. Rapid clearing is expected Monday evening with the exiting low pressure.

While the upcoming storm will be significant for early spring, most of the models have backed off some on storm totals (FYI–this storm is expected to be just a “so- so” event in northern California). I’ve downsized storm totals to 0.75 – 2 inches in the lowlands away from the mountains (from 2 – 3.5 inches). Twice as much could still occur near coastal facing mountain slopes. The initial cold front should produce heavy rain, but it may zip through the region fairly quickly. Occasional heavy intensity showers are likely over the rest of the Easter weekend, but much of the heavier showers are expected close to the mountains. In addition, the center of the “cut-off” low pressure may pass to the south of L.A. County while staying a little too far off the coast. This may lead to less showers in the L.A. County coastal plain on Sunday.

Snow levels should be at or above 6000 feet through early Saturday (falling to 5000 feet by late Saturday evening and possibly as low as 4500 feet Sunday morning). Snowfall at resort level (~6000 feet) may reach at foot, but with the showery nature of most of the storm, total accumulation may be several inches lower or higher in some locales.

Sunny and noticeably warmer weather is expected by Tuesday. Most model solutions show at least a marginal off-shore flow developing on Tuesday (lasting into Wednesday morning). No strong, widespread wind is expected in Santa Ana wind prone areas, but peak gusts in the higher mountains may reach 50 mph for a short time on Tuesday. Assuming it’s a marginal, off-shore flow, warming in the coastal plain may be a little muted, but daytime temperature should still rise into the low/mid-70s. Some readings into the low/mid-80s are likely in the coastal valleys on Tuesday/Wednesday. If a weak but full fledged off-shore flow occurs, several more degrees of warming are probable in some locales (especially near the coast). Cooler weather should occur in the second half of the week (back to seasonable or slightly cooler than normal by the end of next week).

It’s still not a certainty, but a number of model solutions show a minor rain threat on Friday or Saturday next week. The predicted trough may wind up as a “inside slider”. So, it may turn out to be more wind than wet weather (most precipitation falling to the south and east of L.A. County). It’s also possible that the “inside slider” will be too weak to induce relevant showers (just a wind storm for the interior and widespread, marine layer clouds west of the mountains).

Next issued forecast/synopsis may occur on Tuesday, 2 April.