| Day | Date | High/Low | Forecast |
| Mon | 7th | 71/54 | Sunny day with a few high clouds possible. Some evening high clouds. |
| Tue | 8th | 71/56 | Chance of some early morning fog/low clouds; Otherwise, mostly sunny day. Some evening high clouds. |
| Wed | 9th | 76/58 | Sunny day. Mostly clear evening. |
| Thu | 10th | 78/57 | Mostly sunny day with some high clouds. Some evening high clouds. |
| Fri | 11th | 77/55 | Mostly sunny day with some high clouds. Some evening high clouds. |
Synopsis
High pressure aloft has begun to strengthen over southern California. Although it continues to strengthen and expand over the Southwest, (at least through tomorrow morning), surface on-shore flow is forecast (by the computer models) to increase some (already started…reason for minor cooling today in most areas west of the mountains). Satellite imagery showed a swath of low clouds/fog early today along the coast from Orange County southward (still patchy fog present, as of this writing). There was also a batch of shallow low clouds encroaching on some of the outer islands from the. northwest. As a consequence, there may be widespread, coastal fog/low clouds tomorrow morning, especially if a coastal eddy prevails as the models predict. I decided on no temperature change (afternoon high) in today’s forecast but, there is a chance that the coastal plain will be a little cooler tomorrow than it gets today.
On-shore flow should weaken again by later tomorrow and continue through Thursday. At this point, only a marginal off-shore flow is predicted (off-shore toward the north but on-shore toward the east). With high pressure aloft getting moderately strong, good subsidence warming should support valley temperatures reaching the low/mid-90s (by Wednesday). A warming trend is nearly certain for the coastal plain (after tomorrow), but one nagging point (for me) is whether a shallow though diluted marine layer remains (shown by some model forecasts). That would limit the warming trend (peaking low 80s inland coastal plain; 70s closer to the coast, campus included). Should a more defined marine layer exist later into the week, it could remain even cooler (warming to only slightly above normal). I decided to be a little conservative on the campus warming trend.
High pressure aloft is forecast to weaken and move eastward on Friday (approaching upper air trough from the west). Most of the models favor only minor cooling that day (one model shows no cooling that day though). It’s possible that temperatures peak early in the day, and afternoon temperatures will be noticeably lower in the afternoon (strengthening sea breeze pattern). By the weekend, the nearing trough should strengthen the on-shore flow. That, in turn, should support a return of widespread, marine layer clouds this weekend. Temperatures should tumble back to near normal levels over the weekend.
The forecast for next week is a little fuzzy on details. Most of the longer range models show a series of troughs passing through the state next week. That would limit any warming cycles when high pressure aloft passes overhead (at best, getting slightly warmer than normal well inland areas). There is one peculiar forecast showing a large, “cut-off” low pressure affecting southern California for much of next week (by the usually reliable ECMWF model). This scenario not only supports a week of cooler than normal weather, periodic instability showers would be possible. The model majority, however, show nothing of the sort. Thus, for now, I’m not in favor of a chance of wet weather returning next week. Even if the “cut-off” low pressure scenario verifies, positioning and strength of the low pressure will determine if any widespread, relevant precipitation falls on the Southland.
Next issued forecast/synopsis may be on Friday, 11 April.