Weather Synopsis – April 29, 2024

James Murakami

Mon29th67/54Sunny day. Clear evening.
Tue30th69/55Sunny day. Clear evening.
WedMay 1st68/57Mostly sunny except chance of some early morning low clouds. Clear evening.
Thu2nd72/56Sunny day. Clear evening.
Fri3rd71/55Sunny day. Clear evening.


A northwesterly wind flow pattern exists over the state today. Periodic, upper level troughs are forecast to pass nearby, but they should be too far to the north and east to trigger wet weather in the state this week. This includes marine layer induced drizzle. So, the chief forecast problems of the week will be related to the strength of the on-shore flow pattern.

In short, on-shore flow this week should be fairly weak, and any marine layer should be very shallow. The on-shore flow should be weaker tomorrow and on Thursday (compared with today). In fact, if some computer model forecasts are right, a marginal, off-shore flow may take place briefly on Thursday (NAM model most aggressive). While I’ve leaned today’s forecast to favor the off-shore flow scenario, full fledged, off-shore flow events are very uncommon by this time of year. If the predicted, “inside slider” trough ends up weaker than currently predicted, or it passes nearby too far to the east, any surface, off-shore gradient is likely to be just from the north (as has been the case in recent days…one reason for minimal marine layer clouds of late in L.A. County). However, should the off-shore flow actually take place (significant winds only at higher elevations), daytime temperatures near the coast on Thursday are likely to be several degrees higher than currently anticipated (includes UCLA area).

In between days (Wednesday and Friday) are predicted to have ever slightly stronger on-shore flow (compared with Tuesday and Thursday, respectively). That should result in a tad cooler weather in the coastal plain (compared with their respective, previous day). By the weekend, a more lengthy trend of strengthening on-shore flow is predicted by most of the models (more pronounced Sunday-Monday period). The influencing, upper level trough, however, should still be too weak for any rain threat in the state.

The only weather wildcard for this week is the extent of marine layer clouds (a common forecast dilemma by this time of year in southern California). Despite the presence of a weak, coastal eddy circulation early today, low clouds were limited to along and off the coast from about San Pedro southward (low clouds staying just off the coast in parts of Santa Monica Bay). The various models keep the marine layer mostly very shallow or diluted for this week (slightly deeper for brief time Wednesday and more lengthy this weekend). Subtle wind flow pattern shifts could easily allow for more widespread low clouds/fog on any given day this week. This might result in cooler than predicted weather for areas near the coast (campus included). However, for the most part, this week should have slightly warmer than normal weather (particularly Thursday-Friday period).

Next issued forecast/synopsis should be on Thursday, 2 May.