| Day | Date | High/Low | Forecast |
| Mon | 15th | 68/53 | Hazy sunshine remainder of day. Mostly clear evening. |
| Tue | 16th | 75/56 | Mostly sunny day with some high clouds possible. Some evening high clouds possible. |
| Wed | 17th | 75/57 | Mostly sunny day with some high clouds. Some evening high clouds. |
| Thu | 18th | 77/54 | Mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Fri | 19th | 74/52 | Chance of early morning fog/low clouds; Otherwise, mostly sunny day with scattered high clouds. Chance of evening low clouds. |
Synopsis
A weak, upper level trough had sat off the state coast for a couple of days (reason for cool down and marine layer return recently). It moved inland this morning. High pressure aloft should exert weather influence again in southern California for the remainder of the week. Warmer than normal weather for most of the Southland is anticipated. The question mark for the coastal plain is how warm it will be able to get over the next few days. Weak, surface off-shore flow toward the high desert already exists, but it remains weakly on-shore toward the low desert. At least for today, that onshore gradient has promoted persistent low clouds this afternoon from Orange County southward.
Since subsidence warming from the building high pressure aloft should be limited (deep layered winds aloft not predicted to go northeast), a complete purge of the local marine layer may not occur as most computer models have predicted (over predicted that influence for today). Should a shallow but defined marine layer persist beyond today, the coastal plain likely will see only minor warming compared with today’s readings (UCLA may only reach low 70s, at best). Widespread 80 degree weather in the coastal valleys, however, is still likely (marine layer has stayed out of most of those areas). A leveling off of the warming cycle should occur on Wednesday (passing storm well to our north…some minor precipitation for parts of northern third of state). However, high pressure aloft should bounce back on Thursday. That day should be the warmest day of this week.
The models continue to predict a major shift in the eastern north Pacific jet stream by the weekend. High pressure aloft currently off the state coast will gradually get displaced south and east. A large trough should set up somewhere off the West Coast early next week. As often the case, the various models disagree on details, but widespread, wet weather in the state is likely by the middle of next week. Model solutions vary from minor precipitation to flooding type weather (tap into an atmospheric river). Recent model consensus favors wet weather starting in L.A. County by Tuesday evening. Christmas Eve would be the main wet day in the Southland, but some model solutions show continued, significant precipitation on Christmas Day (tapering off day later).
I am leary of accepting any one solution over another at this point. I am relatively confident in a good soaking for much of southern California sometime next week. The predicted tap into an atmospheric river would limit how low the snow level will get in the Southland (probably stay above 7500 feet for the bulk of the storm). Temperature-wise, cooler than normal weather is almost certain for much of next week, but it shouldn’t get as chilly as with typical, Gulf of Alaska storms.
The longer range models disagree on whether a series of storms will pass through the Southland. Dry weather could return as early as Christmas Day or occasional wet weather may occur through at least the 27th. Again, don’t put too much faith in the details of expected weather for now. However, if statistics hold up again, New Year’s Day should be dry.
Next issued forecast/synopsis (last one of year 2025) should be on Monday, 22 December (first full day of winter).