| Day | Date | High/Low | Forecast |
| Mon | 10th | 83/57 | Mostly sunny day with some high clouds developing in the afternoon. Some evening high clouds. |
| Tue | 11th | 77/58 | Chance of early morning fog; Otherwise, mostly sunny day with variable high clouds. Becoming mostly cloudy in the evening. |
| Wed | 12th | 71/59 | Partly to mostly cloudy day. Mostly cloudy evening. |
| Thu | 13th | 63/54 | Mostly cloudy day. Rain developing, possibly heavy at times. Rain tapering off in the evening to a chance of a few showers. |
| Fri | 14th | 62/51 | Partly cloudy day with a chance of showers, mainly in the morning; Possibly breezy at times in the afternoon. Clearing in the evening. |
Synopsis
A large and strong (for November) high pressure aloft covers the Southwest today (responsible for the recent warm up in the state). There is off-shore flow occurring, but this one lacks “muscle” to purge the coastal marine layer (noticeable winds in Santa Ana wind prone areas restricted to higher elevations and not all that strong, as far as Santa Ana winds go). It’s certainly strong enough to promote widespread 90 degree weather in the coastal valleys (isolated readings inland coastal plain too today). However, for areas near the coast, the warming trend has been more muted (none at the coast where a shallow marine layer dominates). UCLA reached the low 80s today, but just a couple miles closer to the coast, it was mostly in the mid-70s and dropping off to the mid-60s around the coast.
All the computer models continue to forecast a significant cooling trend for most areas starting tomorrow (modest at first but gains momentum as the week progresses). This results from an approaching storm system from the Gulf of Alaska. Last week, some models had predicted a sub-tropical, upper low pressure would arrive sometime in the late Tuesday-Wednesday period with showers. More recent model runs altered that low pressure’s path in such a way that it would be absorbed by the Gulf of Alaska system. Widespread wet weather is still expected in southern California, but the time table for that has been pushed back to Thursday (some showers possible San Luis Obispo County Wednesday night though).
Although the models are unanimous predicting wet weather, there remains disagreement (for now) on when showers may start in L.A. County. Some model solutions show the L.A. Basin getting wet by mid-morning Thursday. The slowest scenario delays rain till about sunset. There should be a 4 to 7 hour period of steady rain. Within that time frame, occasional heavy intensity rain is probable (high water vapor content and decent storm dynamics for most areas west of the mountains). Predicted, atmospheric instability is unimpressive, but I wouldn’t rule out a brief-lived thunderstorm sometime during the storm (nothing widespread in areal coverage). On/off, showery weather (versus the steady form) is anticipated by late Thursday evening (L.A. County westward). Unless the storm moves more slowly than current model projections, things should start to settle down Friday evening (sooner if model forecasts too slow). Mostly sunny but cool weather should prevail for Saturday.
As with many of the stronger storms, the models vary with predicted rainfall. For this forecast, a range of 0.75 to 1.50 inches in the lowlands away from the mountains appears reasonable. However, there are scenarios with higher totals (more like 2 inches on the high end). As is often the cast, one can double the totals for areas up against coastal facing mountains. The cold core isn’t forecast to reach southern California till Friday. So, snow levels are expected to be above 7000 feet for most of the event. Even on Friday, snow levels aren’t expected to drop below 6000 feet (up to a few inches of “wet snow” at that lower elevation).
The models show weak high pressure aloft over the Southland on Sunday. However, oddly, one model (ECMWF) predicts some instability showers that day (sufficient, leftover, low level moisture). For now, this solution has been rejected, but if it verifies, no relevant rainfall would be expected (showers mostly along/over the mountains). By Monday, however, a new storm is forecast to pass through the state. Most solution lean in favor of an “inside slider” type storm (more wind than wet weather). Another “inside slider” may pass through the Southland around Thursday next week. A warm weather off-shore flow may occur over the subsequent weekend. While little faith should be taken this far out in time, there are some models predicting a modest storm early in the Thanksgiving week period.
Next issued forecast should be on Thursday, 13 November.