| Day | Date | High/Low | Forecast |
| Mon | 9th | 69/59 | Sunny after low clouds clear late morning. Low clouds returning in the evening. |
| Tue | 10th | 72/60 | Morning low clouds likely but mostly sunny with some high clouds by late. morning. Chance of evening low clouds. |
| Wed | 11th | 73/60 | Good chance of morning low clouds but mostly sunny with some high clouds by late. morning. Chance of evening low clouds. |
| Thu | 12th | 73/61 | Good chance of morning low clouds but mostly sunny with some high clouds by late. morning. Chance of evening low clouds. |
| Fri | 13th | 74/61 | Chance of early morning low clouds; Otherwise, mostly sunny day with some high clouds. Some high clouds in the evening possible. |
Synopsis
A weak, upper level, low pressure that was west of the state has finally moved inland (through the Mohave desert). High pressure aloft will build over the state by tomorrow. It should continue to expand its weather influence into the desert Southwest through this weekend. A new Pacific trough is forecast to weaken the aforementioned high pressure, and the ridge of high pressure should also get displaced to the southeast for a few days next week. If some of the longer range models are right, the high pressure should rebuild back into the Southwest late next week and stick around through at least the subsequent weekend (may get stronger than the one this week).
We’ve reached the time of year where upper level dynamics tend to be weaker than earlier in the year. The on-shore flow pattern (i.e. sea breeze pattern) so common to southern California can be influenced (at times) more from low level forces than upper level ones (latter usually more the rule). This week, on-shore flow has remained stronger than what the computer models have been forecasting. Coastal eddies have countered (so far) the effects by upper level circulations. Most areas within the realm of the marine layer haven’t warmed up as much as was expected last week. The various models continue to insist on weaker on-shore flow for the next few days, but admittedly, they predict only minor weakening (despite the strengthening high pressure aloft). Warmer weather in the subsequent days is a near certainty. The question is by how much.
All the models predict the marine layer will remain a daily, weather fixture in the coastal plain through Friday. The marine layer depth should decrease over time. That, in turn, should lead to less extensive low clouds as the week progresses (all the coastal valleys may be low cloud free by Thursday or Friday). It’s less clear (to me) whether coastal low clouds will get restricted to the immediate coast by the weekend. I’ve leaned the campus forecast for minor warming (getting slightly warmer than normal by Friday). The warming should be more noticeable over the weekend, but confidence is low at this time (I’ve over forecast warming trends of late).
I should point out that some occurrence of vertical air mixing of sufficient strength could disrupt the local, low cloud field. This would help accelerate the warming trend in the coming days (more so nearer the coast than well inland areas…latter should see better warming from the predicted, shallower marine layer). On the other hand, a coastal eddy and predicted, intense desert heating (results from the expected, desert Southwest high pressure ridge aloft) may lead to a stronger than predicted, low level, on-shore flow (i.e. strong sea breeze influence keeps marine layer intact…temperatures stay lower than current expectations west of the mountains).
Assuming the high pressure gets displaced early next week, some enhancement of the marine layer should result (more extensive low clouds and at least a modest, cooling trend for a couple days). Another warming cycle is expected late next week, however, when high pressure should build back into the Southwest. It should be noted that the recent cooling cycles have generally been less in magnitude than preceding ones. Recent warming cycles, for the most part, have trended higher in magnitude than preceding ones (nearly always the case as summer nears…astronomically speaking, summer begins on 20 June at 7:42 PM).
Next issued forecast/synopsis should be on Monday, 16 June.