| Day | Date | High/Low | Forecast |
| Fri | 6th | 71/54 | Sunny remainder of day. Clear evening. |
| Sat | 7th | 76/55 | Sunny day. Clear evening. |
| Sun | 8th | 68/51 | Mostly sunny day with some high clouds except chance of some early morning fog. Chance of evening low clouds. |
| Mon | 9th | 66/50 | Chance of morning low clouds; Otherwise, mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Tue | 10th | 70/50 | Mostly sunny day with scattered high clouds. Mostly clear evening. |
Synopsis
After a couple days of weak, on-shore flow, off-shore flow has returned in earnest. Some valley locales this afternoon have warmed into the mid-80s along with a few wind gusts into the 30s. This is in contrast to most beaches where a lingering marine layer has kept temperatures mostly in the 50s (patchy fog/low clouds hanging tough in spots from Malibu southward, as of this writing). If the numerical models are right, even the beaches should have one day (tomorrow) of temperatures into the low/mid-70s while widespread 80 degree weather occurs for well inland areas. This could include the inland, coastal plain as the models have infrequently under estimated peak temperatures during off-shore flow events. I stayed with the model consensus forecast, but I wouldn’t be surprised if UCLA flirts with the 80 degree mark tomorrow (just need to keep ocean breezes away long enough).
The ridge of high pressure responsible for the off-shore flow should weaken on Sunday. Santa Ana winds should peak tomorrow morning where peak wind gusts may reach 55 mph at higher elevations (should stay under 45 mph at lowland spots that are prone to Santa Ana winds). Since the deep layered, wind direction should shift from north to more easterly, winds should ease up in some areas (those locales that typically see peak winds from a north direction). All areas should see less wind on Sunday although noticeable winds are anticipated through much of the morning hours. A brief return of on-shore flow is expected late Sunday into Monday morning. After the passage of an “inside slider” trough, a new Santa Ana wind event should occur (lasting through mid-week). Another on-shore flow cycle should prevail late next week (magnitude uncertain at this time as model solutions vary).
Today’s model consensus shows a noticeable drop in temperatures on Sunday (compared with the Saturday forecast). A drop is likely, but I have some concern that cooling that day will be more modest than the models show. High pressure aloft isn’t forecast to weaken a whole lot through much of the daytime hours. So, off-shore flow may linger long enough to allow for warmer weather that day. Today’s campus temperature forecast goes with the model consensus, but confidence isn’t the greatest (wouldn’t be surprised if it winds up several degrees higher). By Monday, however, the “inside slider” should promote a short period of on-shore flow accompanied by a shallow marine layer (probable return of low clouds/fog in the coastal plain).
All the models predict off-shore flow for late Monday through Thursday (peak winds Tuesday though warmest day probably will be Wednesday). However, the various models have disagreed on how strong the Santa Ana wind event would be. Some model solutions have favored a strong wind event (peak mountain, wind gusts exceeding 75 mph). On the other end, a much weaker off-shore flow may not get any worse than the current off-shore flow. There would also be repercussions with temperatures (from a “cool” Santa Ana wind to one similar to the current event). For this forecast, I’m leaning toward a weaker event (i.e. one more similar to the current event). The models have generally shifted toward weaker Santa Ana winds (less wind support from the passing “inside slider”). Of course, being several days away, it’s still possible for the models to shift back toward a windier event (cooler as well though peak temperatures should at least reach the low 70s).
At one time, there were predictions of cold air instability showers valid for the upcoming, Monday-Tuesday period (no longer a consideration). There were also predictions for multiple storm opportunities later in the week. That scenario hasn’t changed although the first storm chance may not come till the subsequent weekend (14th-15th)…at least a day earlier in northern California. Most of the model solutions don’t favor particularly wet systems (no direct connection with an atmospheric river). Some models don’t favor anything worse than marginal, “inside sliders” for southern California (more wind storms than wet storms). Model consistency has been lacking so far (one day it’s wet for a particular date only to be followed by dry day with a subsequent run). While there seems a good chance of at least one storm event starting about mid-month or slightly later, I can’t say with any confidence that southern California will be included in the wet zone (potentially limited mostly to northern California). It’s still a “wait and see” situation.
Next issued forecast/synopsis should be on Monday, 9 December.