Weather Synopsis – May 16, 2024

James Murakami

Thu16th66/57Partial afternoon clearing. Low clouds likely in the evening.
Fri17th67/55Morning low clouds likely but sunny afternoon. Low clouds likely by late e evening.
Sat18th67/55Mostly sunny after low clouds clear late morning. Chance of evening low clouds.
Sun19th67/56Mostly sunny after low clouds clear late morning. Good chance of evening low clouds.
Mon20th66/56Mostly sunny afternoon after low clouds clear. Evening low clouds likely.


High pressure aloft has built into the state today, but it hasn’t had a relevant affect on the low cloud field in southern California (so far). The low level, on-shore flow weakened only every slightly, and an intermittent, coastal eddy continues (computer models had predicted a temporary absence of the coastal eddy by now). Clearing of low clouds did occur in some areas (started in San Diego area), but except for a little thinning of the overcast, the Westside remained socked in with low clouds (left forecast unchanged in case a last minute clearing occurs late in the afternoon).

The models continue to forecast only minor day to day changes in the low level, wind flow pattern. The on-shore flow may weaken on some days and strengthen on other days, but the changes should be minor enough to prevent significant changes in the low cloud pattern (at least, for the coastal plain). There is always a chance that some unexpected, vertical air mixing occurs. That could help mix dry air aloft (above the marine layer) down into the low cloud field. The result could be that holes develop in the blanket of low clouds off the Southland coast. A predicted, weak, upper air disturbance could help trigger that mixing (valid over the weekend). I’ve leaned today’s forecast in that direction, but confidence is low. Furthermore, I hedged the temperature forecast with an almost persistence forecast. Even if better clearing occurs on a given day, the on-shore flow should remain too strong to allow for noticeable warming in the coastal plain. Even the coastal valleys probably won’t warm back to seasonal normals during the next few days.

Most of the longer range models aren’t predicting any major changes, weather-wise. Multiple, upper level troughs are forecast to pass near or over southern California next week. These troughs are expected to be “inside slider” troughs (mainly wind storms for interior sections). The marine layer may get deep enough for spotty, early morning mist/drizzle on occasion. In short, more “May Gray” weather is probable for the next week or so. If some model solutions are right, it may persist right through the subsequent, Memorial Day weekend. Some warm weather that includes the coastal plain is certain to come (summer is a little over the month away). It just may take awhile.

Next issued forecast/synopsis may occur on Tuesday, 21 May.