| Day | Date | High/Low | Forecast |
| Mon | 22nd | 69/60 | Hazy sunshine remainder of day. Clear evening. |
| Tue | 23rd | 74/62 | Chance of some early morning low clouds; Otherwise, mostly sunny day with some high clouds. Scattered evening high clouds. |
| Wed | 24th | 76/63 | Partly cloudy day with mainly mid/high clouds. |
| Thu | 25th | 75/61 | Chance of some early morning low clouds; Otherwise, mostly sunny day. Mostly clear evening. |
| Fri | 26th | 74/59 | Chance of early morning low clouds; Otherwise, mostly sunny day. Chance of late evening low clouds. |
[Note: Forecasts issued just once a week for the summer]
Synopsis
High pressure aloft is building across the desert Southwest today. It should strengthen through tomorrow and level off on Wednesday (at least, that’s what most of today’s computers project). The marine layer was shallower this morning compared with over the weekend, and the shrinking depth trend should continue through tomorrow (possibly into Wednesday morning). The shallower marine layer, along with weaker on-shore flow, has promoted modest warming for inland areas (more minor closer to the coast). Several more degrees of daytime warming is expected tomorrow before leveling off on Wednesday.
As has been the case multiple times the this month, figuring out how much warming would take place at UCLA has been challenging for me. I’ve over predicted some of the warming cycles (under predicted a couple times too). A shallow but well defined marine layer can limit vertical air mixing near the coast. Today wound up a bit warmer than I predicted, but I didn’t amend the temperature forecasts for Tuesday and Wednesday due to this uncertainty (of how much mixing may take place).
Starting tomorrow, an influx of “monsoon” moisture aloft will enter southern California. Deep layered moisture and instability should remain above 10000 feet elevation, but for the Southland mountain/desert region (mainly southeastern portion), there will be a chance for isolated, brief-lived thunderstorms (mainly Tuesday/Wednesday afternoons). Variable mid/high clouds should gradually cover areas west of the mountains. Should vertical air mixing reach the ground in the coastal plain, it could actually promote a lot higher temperatures than I show in this forecast (much more muggy too). That, in turn, may disrupt the local marine layer (little to no low clouds inner coastal waters). The currently forecast cooling trend in the latter half of the week may get delayed by a couple days.
On way or another, an upper level, Pacific trough is forecast to develop over much of the West by the weekend. So, a noticeable cooling trend should develop (all of southern California, not just the coastal plain). Potentially, widespread “June Gloom” weather is possible for the Sunday-Monday period (Monday currently forecast to be the coolest over the next week). A new warming cycle is anticipated by the middle of next week, but there isn’t great agreement on how much warming will take place (leaning toward slightly warmer than normal before 4th of July…some model forecasts include a “monsoon” moisture incursion).
Next issued forecast/synopsis should be on Monday, 29 June.