| Day | Date | High/Low | Forecast |
| Fri | 15th | 67/57 | Postcast High temperature…Possible partial afternoon clearing; Otherwise, mostly cloudy through the evening. |
| Sat | 16th | 68/56 | Amended High temperature…Possible partial afternoon clearing; Otherwise, mostly cloudy through the evening. |
| Sun | 17th | 67/56 | Morning low clouds likely but mostly sunny afternoon with some high clouds; Possibly breezy at times in the afternoon. Chance of evening low clouds. |
| Mon | 18th | 71/55 | Chance of some early morning low clouds; Otherwise, mostly sunny day with some high clouds. Some evening high clouds. |
| Tue | 19th | 72/57 | Mostly sunny day with some high clouds. Some evening high clouds. |
Synopsis
A belt of high pressure aloft in the northeastern Pacific extends to southern California today. At the surface, a strong on-shore flow pattern exists. All this has favored “May Gray” weather west of the mountains (has mostly cleared Inland Empire southward to San Diego County, as of this writing though). A couple of “inside slider” type troughs will pass near the Southland this weekend. The troughs should help maintain a good on-shore flow pattern (even windier at times in the interior). A deep marine layer should continue west of the mountains, but subtle changes in the low level winds may result in better clearing in places over the weekend (not necessarily same locales each day).
The second “inside slider” on Sunday may actually help disrupt the local, low cloud field. So, don’t be surprised if Sunday winds up a sunnier day than what I expect tomorrow. An influx of cooler air should keep temperatures lower than what might otherwise occur if Sunday has mostly sunny skies. As often the case, the complexities of marine layer physics keeps me unsure of my forecast (mainly in the cloud forecast). Sunny or mostly overcast, daytime temperatures in southern California should be slightly cooler than normal (influx of cooler air from the “inside sliders”.
By Monday, most of the computer models predict a brief period of off-shore flow. One model (NAM) is the most enthusiastic about a short duration, Santa Ana wind event. Potentially, higher mountains could see peak wind gusts reaching 55 mph (Santa Ana wind prone areas at low elevations could see peak winds at 35 mph). Since the overall, wind flow pattern isn’t conducive for widespread, significant wind in the lowlands, I’m skeptical of the stronger wind scenarios (at this time). However, isolated, peak, higher mountain gusts to 50 mph wouldn’t be an unreasonable forecast.
Assuming warm air from aloft mixes into the low clouds, Monday should be a mostly sunny day (kept a chance of some early morning, low clouds as a just in case). My chief uncertainty for Monday is how much warming could occur west of the mountains. Some well inland areas should reach the low/mid-80s, but close to the coast (campus included), a lingering marine layer (even a diluted one) could limit the warming potential to the mid-70s. I stayed conservative for this forecast as I’ve been over forecasting temperatures during predicted warming cycles.
Temperatures in the coastal plain shouldn’t stray too far above normal temperatures next week. Although a belt of high pressure aloft is predicted around the Southland, a number of model solutions show some form of trough off the Southland coast. This may help reorganize marine layer clouds as next week progresses. Some model solutions show potential for another spate of “May Gray” weather by the subsequent weekend.
Next issued forecast/synopsis should be on Monday, 18 May.