| Day | Date | High/Low | Forecast |
| Mon | 12th | 67/55 | Mostly sunny with some high clouds after morning low clouds clear; Possibly breezy at times in the afternoon. Evening low clouds becoming likely. |
| Tue | 13th | 66/53 | Morning low clouds likely; Mostly sunny afternoon and possibly breezy at times. Partly cloudy evening. |
| Wed | 14th | 67/55 | Partly cloudy through the evening. |
| Thu | 15th | 67/56 | Mostly sunny after morning low clouds clear. Chance of evening low clouds. |
| Fri | 16th | 65/56 | Mostly sunny after morning low clouds clear. Evening low clouds likely. |
Synopsis
Well, it got warmer than I expected across the Southland late last week. Many valley locales reached triple digits on Saturday (a record for the date 103 degrees in Woodland Hills, for example). Even near the coast, UCLA reached the 90 degree mark for the first time this year (91 degrees on the 10th was just one degree shy of the record for the date set in 1934). Only at water’s edge did the temperature fail to exceed the 60s. Weaker than expected (by me) on-shore flow and decent, vertical air mixing were the culprits. While noticeably cooler yesterday (compared with the day before), it was still a much warmer than normal Mother’s Day in most area (key exception being at the beach).
A large, upper level trough currently lies over the West Coast today. Some cold air instability showers have occurred over parts of northern California (mainly around the mountains). In southern California, strong on-shore flow has returned (Nature’s air conditioner substantially cooling much of the Southland). This trough is forecast to sag farther to the south through tomorrow. So, temperatures in most areas should lower a bit more on Tuesday (more pronounced well inland areas than near the coast). The breezy weather in the interior should continue and possibly expand in areal coverage. The afternoon sea breeze should blow more briskly tomorrow than today.
With the trough center making nearest approach tomorrow, there is some chance for marine layer induced drizzle or light showers in the morning (mainly early hours). This should take place mostly around coastal facing foothills/mountains. However, there are some model forecasts of no widespread overcast (low cloud field may get disrupted). This condition would last into Wednesday. Regardless of whether a widespread, solid overcast occurs west of the mountains or not, the aforementioned trough will promote continued cooler than normal weather.
The trough should weaken and shift farther to the east after tomorrow. However, other “short wave” troughs should leave some portion of the large trough over the Southland. This should promote mostly cooler than normal weather for the remainder of the work week (at best, a minor warming trend for inland locales). If the local, low cloud field does get disrupted tomorrow, it should be “repaired” by Thursday (i.e. widespread, morning overcast west of the mountains). At this point, I don’t see an episode of “May Gray” weather in the coastal plain (i.e. overcast lingering into the afternoon hours), but confidence is low.
Most of the longer range models show another trough moving into the West Coast this weekend. The models disagree on how strong the southern end of the trough will be, but some model solutions show some potential for widespread, marine layer, light rain Saturday morning (instability showers possibly on Sunday but mostly around the mountains). I’m confident on cooler than normal weather this weekend (possibly cooler than it gets today), but confidence in any wet weather is still quite low. If the trough winds up weak, the most that could happen is spotty, early morning mist.
Warmer weather is forecast to return by the middle of next week and continue for several days (probably through the subsequent weekend. There is some potential for much warmer than normal, but a number of model solutions keep the high pressure center too far away (from southern California). Local forces (i.e. sea breeze pattern) may keep temperatures more tempered compared with well inland areas. So, for now, I don’t see a repeat of the recent heat happening late next week.
Next issued forecast/synopsis may be on Friday, 16 May.