| Day | Date | High/Low | Forecast |
| Fri | 30th | 84/64 | Amended high temperature…Sunny remainder of day. Some evening high clouds possible. |
| Sat | 31st | 82/66 | Amended high temperature…Generally partly cloudy with mid/high clouds through the evening. |
| Sun | 1st June | 76/60 | Partly to mostly cloudy with mid/high clouds through the evening. |
| Mon | 2nd | 72/59 | Good chance of morning low clouds but sunny afternoon. Evening low clouds returning. |
| Tue | 3rd | 70/58 | Good chance of morning low clouds but sunny afternoon. Chance of evening low clouds. |
Synopsis
A “cut-off” low pressure was spinning just west of central Baja California today. There was deep layered, easterly wind flow aloft, which often favors significant warming (off-shore flow). However, early today, a shallow marine layer fostered low clouds from the South Bay area southward. Thus, I thought warming near the coast would be more tempered than the off-shore flow aloft would suggest. The computer models also showed only modest warming near the coast. Well, sub-tropical aloft mixed down to the ground in most areas by late morning. That led to a big warm up for areas more than a couple miles from the coast (also for elevations higher than a couple hundred feet in the Santa Monica mountains). That’s the reason for my amended forecast (really a postcast…84 degree maximum as of 1:46 PM).
The “cut-off” low pressure is forecast to drift a little westward for a little while before it starts moving northeast late tomorrow (headed for Arizona). The wind flow in the eastern hemisphere of the low pressure should import increasing “monsoon” moisture aloft into southern California (already a bit muggy today). Varying amounts of mid/high clouds should prevail tomorrow and Sunday. Although tropical storm Alvin (a few hundred miles south of the southern tip of Baja early this afternoon) is forecast to dissipate as it travels northward, a surge of the tropical storm, deep layered moisture should work its way up the Gulf of California. Sufficient atmospheric instability is forecast to promote isolated showers/brief-lived thunderstorms tomorrow afternoon for the southeast corner of the state. There is some chance that parts of the Southland (not limited to mountain/desert region) could see light showers Saturday night into Sunday. A better chance of mountain/desert thunderstorms should occur by Sunday afternoon. I did not include a chance for light showers in the campus forecast, but don’t be surprised if sprinkles occur in the L.A. Basin Sunday morning.
The weekend temperature is a tricky one. Increased “monsoon” moisture should favor thicker clouds (i.e. lessen solar heating compared with today). The various models also predict increasing surface on-shore flow. These conditions should support lower temperatures tomorrow (more so on Sunday when the “cut-off” low pressure makes closest approach…predicted center never entering state though). However, continued vertical air mixing is expected (just not as vigorous as today…I think). That should favor temperatures as high, if not somewhat higher than it gets today (some triple digit readings noted in the valleys today). My amended forecast for Saturday leans toward minor cooling relative to today, but admitted, confidence isn’t high. Even if cooling ends up more noticeable, it should still be warmer than normal away from the immediate coast.
On Monday a different, “closed”, upper low pressure is forecast to approach southern California (coming from the northwest). Although this low pressure should help shunt “monsoon” moisture east of the state, on-shore flow should increase significantly. So, a return of widespread, marine layer clouds (west of the mountains) should occur Monday and Tuesday (passage of the low pressure by Tuesday afternoon). This low pressure is forecast to be weaker than some models showed last week, but cooler than normal weather should nonetheless occur early next week (areas near the coast struggling to pass the 70 degree mark). It’s also quite possible that spotty, early morning mist/drizzle will occur (Tuesday has somewhat better chance, in theory). There’s also some chance that “June Gloom” weather will occur (i.e. persistent low clouds even into the afternoon hours).
While the Tuesday low pressure should move east sometime Tuesday, the model consensus favor some vestige trough remaining for rest of next week. The trough should be pretty weak, which should allow for a warming trend after Tuesday. However, if a shallow but defined marine layer prevails, any warming trend near the coast (campus included) should be modest at best (better warming for well inland areas though…slightly warmer than normal by second half of next week). For the time being, the model consensus doesn’t predict a return triple digit heat for the coastal valleys next week.
Next issued forecast/synopsis may be on Monday, 2 June. [Note: I am planning to switch to once a week forecasts after next week…as I did last summer.]