| Day | Date | High/Low | Forecast |
| Fri | 22nd | 68/58 | Low clouds clearing hazy sunshine in the afternoon. Low clouds in the evening. |
| Sat | 23rd | 68/58 | Low clouds clearing hazy sunshine in the afternoon. Low clouds in the evening. |
| Sun | 24th | 68/58 | Low clouds clearing hazy sunshine in the afternoon. Low clouds in the evening. |
| Mon | 25th | 67/57 | Low clouds clearing hazy sunshine in the afternoon. Low clouds in the evening. |
| Tue | 26th | 67/57 | Low clouds clearing hazy sunshine in the afternoon. Low clouds in the evening. |
Synopsis
An off-shore flow earlier in the week proved it had more “muscle” than I expected. 90 degree weather in the valleys was anticipated, but I had doubts about how warm areas near the coast (UCLA included) would get. Though significant wind was restricted to higher elevation locales, the off-shore flow was well defined on Tuesday (less so by Wednesday). The biggest surprise for me was that the off-shore flow managed to weaken ocean breezes late in the afternoon. So, there was renewed warming late in the afternoon in some places. For some locales like UCLA, the day’s high temperatures on Tuesday occurred after 5 PM (80 degrees at 7:31 PM). The Santa Monica pier warmed to 69 degrees around 5:30 PM and stay so through 7:30 PM (max for the afternoon had been 65 degrees prior to 5 PM).
The off-shore flow was replaced by on-shore flow by yesterday (rather strong today…breezy in the interior this afternoon). All the computer models predict on-shore flow of varying strength through the Memorial Day weekend (probably lasting for a few more days after that). That is one reason for me putting the forecast on auto-pilot today. As is commonly the case, even subtle day to day changes in the wind flow pattern can alter the “behavior” of marine layer clouds (i.e. how extensive and persistent low clouds are on any given day). There is some chance that “May Gray” weather will be more pronounced on some days than others (Memorial Day, for instance). However, I’m not confident enough to write it into today’s forecast. Regardless of the outcome, daytime temperatures changes in the coastal plain this holiday weekend should be minor (a bit more noticeable in the coastal valleys, depending on how persistent low clouds get on a given day).
Most of the longer range models show a “closed”, upper low pressure developing in Nevada by Thursday. Model solutions vary on strength as well as proximity to southern California. Details on predicted on-shore flow may depend on the position/strength of the expected, “closed” low. For now, “May Gray” weather is expected to continue through at least midweek. It could last through Friday, however. A modest warming trend could still develop at the end of work week as the model consensus does weaken the low pressure (also gets nudged east). Some model solutions show slightly warmer than normal weather returning for the subsequent weekend (far from certain though).
Next issued forecast/synopsis should be on Tuesday, 26 May.