| Day | Date | High/Low | Forecast |
| Mon | 18th | 76/63 | Sunny remainder of day. Chance of late evening low clouds. |
| Tue | 19th | 78/64 | Chance of early morning low clouds; Otherwise, mostly sunny day with some high clouds. Some evening high clouds. |
| Wed | 20th | 82/67 | Mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Thu | 21st | 84/69 | Partly cloudy through the evening with high clouds. |
| Fri | 22nd | 86/69 | Partly cloudy through the evening with high clouds. |
Synopsis
This summer, overall, has been relatively mild (so far). There have been a number of warmer than normal days (a few much warmer than normal, especially for well inland areas), but the summer, overall, has been cooler than normal (again, so far). Areas near the coast (UCLA included) have fared well thanks to a mostly, decent strength, on-shore flow (supporting a defined marine layer). Warm periods have been generally short duration so far (above normal temperatures mostly under three days duration).
Well, if the current, computer model consensus holds up, we may see the longest duration heat spell of the summer. High pressure aloft is building back into the Southwest (as it typically does in summer). Unlike a number of high pressures this summer, this one is predicted to be accompanied by fairly weak, surface on-shore flow (instead of moderately strong). In addition, there is definite potential for sub-tropical air to mix down to the ground. That air is predicted to be part of a “monsoon” moisture incursion into southern California (from Arizona/northwest Mexico). The mixing of air should disrupt the low cloud field for several days (nature’s air conditioner becoming much less affective in moderating warm cycles).
Based on today’s model output, some minor to modest warming (latter applicable to well inland locales) is expected tomorrow. More noticeable warming should affect all areas on Wednesday/Thursday as high pressure aloft gets stronger. For this forecast, I’ve taken a more conservative stance with today’s forecast (been over forecasting warm spells most of the summer). However, I wouldn’t be surprised if it winds up warmer (flirting with the 90 degree mark by Friday). The predicted mixing of sub-tropical air down to the ground should also favor warmer overnight, low temperatures (more than has happened so far this summer). Don’t be surprised if the campus doesn’t cooler below the low 70s (again, above forecast taking a conservative view). Surrounding hills and lower mountain slopes potentially may not get much below 80 degrees on some overnights later this week.
All the models predict a “monsoon” moisture incursion into the Southland later this week (starting with varying amounts of mid/high clouds). However, there remains some disagreement on how significant the moisture incursion will get. Deep layered moisture may continue to remain mostly east and south of the state. Isolated, brief-lived thunderstorms may occur daily beginning as early as Thursday afternoon, but it’s uncertain if widespread, significant thunderstorms will ultimately form (valid period this weekend in mountain/desert region). At this time, only variable mid/high clouds are predicted west of the mountains (muggier than normal, however).
It may cool somewhat this weekend compared with what’s expected on Friday, but warmer than normal weather over most of the Southland is expected well into next week (possibly all of next week). The desert region potentially could get slightly cooler than normal under a “monsoon” incursion, but it would be offset by much more humid weather out there. Drier air should develop sometime early next week, but some model solutions indicate another moisture increase late next week. Of course, a small error in predicted winds could lead to a noticeably different, weather outcome.
Next issued forecast/synopsis should be on Monday, 25 August.