Weather Synopsis – May 9, 2024

James Murakami

Thu9th68/56Sunny after low clouds clear late morning. Low clouds likely returning in the evening.
Fri10th67/56Morning low clouds likely but mostly sunny by midday. Chance of evening low clouds.
Sat11th68/55Chance of morning low clouds; Otherwise, mostly sunny day. Chance of late evening low clouds.
Sun12th70/54Chance of early morning low clouds; Otherwise, mostly sunny day. Chance of late evening low clouds.
Mon13th69/54Chance of early morning low clouds; Otherwise, mostly sunny day. Chance of late evening low clouds.


The marine layer deepened some overnight. It resulted in more widespread, low clouds this morning than yesterday. The clouds did clear away by midday, however. I was a bit surprised that temperatures in many areas got a little higher today than I anticipated. Though the marine layer was deeper, better vertical air mixing apparently took place to promote the warming.

Today’s computer model forecasts show a trend toward a shallower marine layer for the next few days (i.e. less extensive low cloud coverage in the morning hours). Subtle changes in the wind flow pattern could result in noticeably different weather with regard to the low cloud pattern (particularly relevant when coastal eddies are involved). For this forecast, I’ve stuck with minor changes in weather for the coastal plain. However, if some of the model forecasts are right, building high pressure aloft for the weekend may result in warmer weather than I show in this forecast (UCLA potentially in the mid-70s on Mother’s Day). The main region for warming this weekend should be for well inland areas where the marine air influence should be weaker.

There have been some cloud build ups over some of the mountains this afternoon. An elongated, “cut-off” low pressure over the southern Great Basin states should be closest to southern California tomorrow (predicted center near Las Vegas). Most of the models don’t show much atmospheric instability, but there is a chance for brief, isolated showers or even a thunderstorm tomorrow afternoon (southern mountains and adjacent desert). Depending on where any shower clouds form, it’s possible for winds aloft to carry them into the valleys of the Inland Empire. The shower threat, however, should end by the evening hours. With the upper low pressure moving east, the weekend weather out there should return to the mundane side.

A new, weak, upper low pressure is predicted to approach the Southland from the west early next week (passing overhead on Tuesday). Other than favoring stronger on-shore flow and a deeper marine layer, no big weather change is expected. The only potential exception west of the mountains might be is the chance for a brief, widespread “May Gray” episode. Most of the longer range models show high pressure rebuilding back into the Southland for the second half of next week. It’s not predicted to be a strong high pressure, but temperatures in most areas should get slightly warmer than normal (similar to what’s expected this weekend). The high pressure probably won’t be strong enough to dilute the marine layer. So, areas near the coast should continue to experience late night/early morning low clouds later next week.

Next issued forecast/synopsis may occur on Tuesday, 14 May.