Weather Synopsis – May 2, 2024

James Murakami

Thu2nd67/55Partial afternoon clearing. Becoming mostly cloudy in the evening.
Fri3rd67/55Possible partial afternoon clearing; Otherwise, mostly cloudy through the evening.
Sat4th66/53Mostly cloudy through the evening; Possibly breezy at times in the afternoon. Chance of light showers in the evening.
Sun5th67/52Some clouds in the morning; Otherwise, mostly sunny day and possibly breezy at times in the afternoon. Clear evening.
Mon6th69/53Sunny day. Mostly clear evening.


The marine layer got deeper than most computer model forecasts showed a few days ago. That resulted in widespread, low clouds west of the mountains (yesterday and today) as well as staying cooler than anticipated. In addition, the predicted, marginal off-shore flow for today was weaker than most models forecast. North winds aloft did punch some holes in the low cloud field early this morning, but the dilution of the marine layer wasn’t enough to promote significant warming (where it cleared relatively quickly). For the most part, temperatures near the coast haven’t changed today from yesterday’s readings.

Today’s campus forecast reflects the current status of the marine layer and on-shore flow pattern. Forecast thinking has also changed from earlier model projections regarding the weekend weather. A few days ago, there were some model solutions showing minor wet weather near the Oregon border (valid at the beginning of the weekend). The latest model forecasts show a chance of rain reaching southern California (valid late Saturday or early Sunday). Saturday could be a cloudy day for most areas west of the mountains. Parts of northern California should get decent precipitation (for May). The high elevations of the northern Sierras are likely to get several inches of late season snowfall. In southern California, the accompanying cold front may bring a brief period of light rain to most areas west of the mountains. I had entertained the possibility of marine layer drizzle for some areas, but low level winds may be favorable enough for frontal rain (at least, that’s what the model consensus shows today). The chief uncertainty is whether the wet weather occurs Saturday evening or in the pre-dawn hours of Sunday (total time in any given location away from the mountains should be under three hours duration).

Even among the wetter solutions, only minor precipitation is predicted. Storm totals should be mostly under a tenth inch (maybe only trace amounts for some areas). Some favored spots up against coastal facing foothills/mountains could receive up to a third inch of rain. At resort level, up to a couple inches of “wet” snow could fall. Atmospheric instability should be lacking with this storm. So, no thunderstorms are anticipated in the Southland.

Even if showers occur later than most model solutions show today, most of Sunday should be sunny. Brisk winds following the cold front should help dry out the atmosphere. The polar air following the front, however, should limit warming that day (even where it’s clear for the entire day). Better warming is expected as the week progresses. At this point, the predicted wind flow pattern doesn’t favor warmer than normal weather (includes well inland locales). Like this week, there is uncertainty about how the marine layer will evolve next week. The low cloud field should be disrupted with the predicted cold frontal passage, but a new blanket of low clouds could reform by the middle of next week. This would be aided by the model consensus forecast of a broad though weak area of low pressure aloft somewhere around the Southwest. Whether a spate of “May Gray” weather occurs next week is still uncertain. However, for the coastal plain, I do expect to see at least some low clouds each day by the latter half of next week (temperatures at or slightly below normal levels).

Next issued forecast/synopsis may be Tuesday, 7 May.