| Day | Date | High/Low | Forecast |
| Mon | 29th | 75/59 | Sunny remainder of day. Mostly clear evening. |
| Tue | 30th | 75/61 | Mostly sunny day except chance of some early morning low clouds. Mostly clear evening. |
| Wed | 31st | 76/61 | Mostly sunny day except chance of early morning low clouds. Some evening high clouds possible. |
| Thu | 1st August | 78/63 | Mostly sunny day with scattered high clouds. Partly cloudy evening. |
| Fri | 2nd | 80/65 | Partly cloudy day with a slight chance of light showers early. Variable evening clouds. |
Synopsis
Note is an amended forecast from the one issued this morning.
I was skeptical last week that seasonable or slightly cooler than normal weather would occur by early this week (prediction by the consensus of computer models). As it turned out, a weak Pacific trough aloft moving inland over northern California did just that. In addition, some slightly drier surface air reached parts of the southern California coast (helped make it the coolest morning today at UCLA since the end of June).
A second weak trough will pass inland through the Pacific Northwest states tomorrow. That should prevent high pressure aloft (centered over New Mexico) from bulging much into the state through tomorrow. Some model forecasts indicate a slight decrease in on-shore flow (Pacific Northwest trough may stay too far north to affect pressure patterns in the Southwest). That may result in some minor warming tomorrow, but that should apply to mainly well inland areas. A weather wild card for the coastal plain, however, might be a temporary return of widespread, coastal low clouds (present in some areas of the Southland coastline early today). That may delay any daytime, warming trend till Wednesday or even Thursday.
Most of the models are predicting a “monsoon” moisture incursion beginning late Wednesday or early Thursday. It should start out minor (just some high clouds). A number of model solutions show a disturbance (currently around southern Baja California) moving northward and potentially passing through coastal, southern California (early Friday). Much could change between now and Friday (disturbance might bypass the local area), but since I’m issuing only one forecast this week (sorry, no second forecast later in the week), I decided to amend the forecast (particularly for Friday period). If the disturbance travels the coastal route, there could be some chance for brief-lived thunderstorms west of the mountains (in addition to plain shower clouds). However, the models aren’t inclined toward any widespread, measurable rain event west of the mountains (may barely wet the ground in the coastal plain). This shouldn’t apply to the mountain/desert region where isolated thunderstorms could produce brief downpours (mainly afternoon hours)
One potential fallout from the predicted passage of the disturbance is a thorough mixing of subtropical air down to the ground. Not only would it get rather muggy (L.A. standards), Friday temperatures might spike much higher than currently forecast (UCLA potentially could reach the upper 80s…flirting with triple digits in some coastal valley locales). The muggy weather west of the mountains could persist through the weekend. Otherwise, the “monsoon” boundary should edge back to the interior sections of the Southland (usual position during incursions).
Depending on which model solution is right, the “monsoon” flow could continue well through next week (potential for flash flooding in some mountain/desert locales at times). Warmer than normal weather is likely for the Southland next week. Just how warm remains to be seen (some usual uncertainties of how strong on-shore flow will be as well as predicted position of high pressure aloft).
Next issued forecast/synopsis should be on Monday, 5 August.