| Day | Date | High/Low | Forecast |
| Fri | 11th | 74/57 | Mostly sunny day with scattered high clouds. Chance of evening low clouds. |
| Sat | 12th | 70/55 | Good chance of morning low clouds but mostly sunny afternoon with some high clouds. Evening low clouds likely. |
| Sun | 13th | 68/54 | Morning low clouds likely; Partial afternoon clearing. Evening low clouds likely. |
| Mon | 14th | 68/53 | Chance of morning low clouds; Otherwise, mostly sunny day with some high clouds. Chance of evening low clouds. |
| Tue | 15th | 67/53 | Chance of morning low clouds; Otherwise, mostly sunny day. Chance of evening low clouds. |
Synopsis
Although high pressure aloft has weakened and moved eastward a little since yesterday, temperatures today are about the same or even a bit higher than it got yesterday. I thought an earlier sea breeze today was going to prevent UCLA from warming more than it got yesterday (75 degrees), but Mother Nature had other ideas (did briefly cool to the low 70s after peaking at 77 degrees but back to 76, as of 3:30 PM).
All the computer models predict increasing on-shore flow ahead of an approaching, weak, upper level trough (from the west). A narrow swath of low clouds/fog occurred early today from about Palos Verdes southward. The low cloud field should increase in areal coverage this evening (some dense fog possible along the coast at first). By tomorrow morning (daylight hours), widespread low clouds in the L.A. County, coastal plain is expected. Depending on the location of a predicted, coastal eddy circulation, low clouds may spread northward along the coast to include Ventura/Santa Barbara Counties. The low clouds should dissipate by afternoon in most areas, but some high clouds should continue like today. This return to on-shore flow will result in noticeable, daytime cooling west of the mountains (relative to today).
The upper level trough should be covering the state on Sunday. So, the wind flow pattern may support more persistent low clouds that day (i.e. possibility of limited, afternoon clearing in spots). There could even be some chance at spotty, early morning mist (mainly up against coastal facing foothills/mountains). The cooling trend should continue on Sunday, but the 24 hour change should be less pronounced than the previous day. Modest cooling should also occur in the interior with the upper air trough more squarely over the region.
The trough should weaken on Monday. A marine layer is expected to continue, but daily clearing of low clouds should be more complete than what may happen on Sunday. Daytime temperatures for well inland areas may also increase a little, but any warming should still be no higher than seasonable levels. Little change in the weather is anticipated on Tuesday (just minor shifts in the wind flow pattern affecting southern California).
The longer range models predict a “closed”, upper level low pressure approaching. It originates from the sub-tropics. While the numerical models aren’t predicting it explicitly (so far), there is some chance that the low pressure could tap into high, water vapor content air. So, accompanying atmospheric instability may promote showery weather sometime in the second half of next week. Much will depend on the strength of the low pressure when it nears the Southland as well as it trajectory (i.e. how close its center gets). If it’s too weak, instability showers would be very isolated (mainly around higher mountains…also little or no chance for thunderstorms). If the low pressure center remains too far away at nearest approach, areal coverage of wet weather would likely be limited (potentially excluding L.A. County). For now, I’m only relatively confident on cooler than normal weather happening in the second half of next week.
The aforementioned, low pressure should move east of the region sometime at the end of next week. Weak, upper level high pressure should move over the Southland over the subsequent weekend (temperatures at or slightly above normal). For the week of the 20th, most model solutions favor a northwest wind flow pattern on the West Coast. This would favor occasional, “inside slider” type troughs to pass through or near the state. Chances for wet weather with any of the troughs should be quite limited (marine layer induce showers, at most). Temperatures should be mostly on the cooler than normal side (not by a lot, though).
Next issued forecast/synopsis may be on Monday, 14 April.