| Day | Date | High/Low | Forecast |
| Tue | 8th | 89/75 | Showers ending noon hour and becoming partly cloudy. Partly cloudy evening. |
| Wed | 9th | 93/73 | Partly cloudy through the evening. |
| Thu | 10th | 89/69 | Partly cloudy through the evening. |
| Fri | 11th | 84/67 | Some clouds but mostly sunny day. Mostly clear evening. |
| Sat | 12th | 82/64 | Some early morning low clouds possible; Otherwise, mostly sunny day. Mostly clear evening. |
Synopsis
Well, the weather of recent days was not what I ordered. The Labor Day weekend began warmer than I anticipated (should have seen it though with all that predicted, subtropical air preceding moisture from then hurricane Marie). While some computer models did predict significant rain for parts of southern California (included L.A. Basin in some scenarios), Sunday afternoon was supposed to be mostly dry west of the mountains (many locales remained wet, intense at times around UCLA). Record rainfall for the dates (6-7 September) occurred on campus (storm total 1.18 inches…some totals reached over 1.5 inches in the hillsides north of UCLA). I was most surprised by the occasional showers yesterday and today (included thunderstorms in places today…closest near Santa Monica airport late morning though little in the way of rainfall there).
The various models handled today’s shower activity poorly (was supposed to have been almost entirely in mountain/desert region). Today’s model output insists tomorrow’s showers/thunderstorms will be over the southern mountains and eastern desert (nothing west of the mountains). That scenario looks plausible this time as recent radar data shows storm motions more south to north than earlier (southwest to northeast). The shift in winds aloft should cut off the supply of moisture from former hurricane Marie (now just a huge but still breezy, coastal eddy over 700 miles southwest of Los Angeles). The shifting winds should continue to funnel “monsoon” moisture over Mexico into the Southland but more over the interior. Unfortunately, reduction in humid weather west of the mountains should be a slow process (tomorrow should be almost as muggy as today in many locales).
The models maintain ample upper level moisture over most of the Southland through Thursday. I worded the cloud forecast with “partly cloudy”, but the clouds may be more variable in thickness. If clouds remain on the thicker side (blotting out the sun), it shouldn’t get as warm as I show in today’s forecast. A predicted, upper level trough in the Pacific Northwest will help displace the current, intensifying high pressure in the desert Southwest. So, a noticeable, cooling trend should begin by the end of the week. Model agreement though isn’t great on how much cooling will take place (potentially not getting cooler than normal in the coastal plain). Whatever cooling cycle may get reversed around the middle of next week. At this point, that warming period should be relatively minor.
Longer range model forecast show more troughing on the West Coast as we near astronomical autumn (22nd). Some model solutions favor a foretaste of cool, autumn temperatures (for L.A.). Others favor less cooling (seasonable for late September). A few solutions show high pressure nearby and funneling “monsoon” moisture again. It’s a “wait and see” situation.
Next issued forecast should be on Monday, 14 September.