| Day | Date | High/Low | Forecast |
| Thu | 23rd | 70/56 | Mostly sunny day with variable high clouds. Scattered evening high clouds. |
| Fri | 24th | 70/56 | Chance of early morning low clouds; Otherwise, mostly sunny day with scattered high clouds. Chance of evening low clouds. |
| Sat | 25th | 66/54 | Mostly cloudy through the evening. Slight chance of morning, light showers. Good chance of light showers late afternoon- evening period. |
| Sun | 26th | 66/54 | Partly cloudy day with chance of overnight showers ending early. Possibly breezy at times in the afternoon. Chance of evening low clouds. |
| Mon | 27th | 67/54 | Partly cloudy through the evening. |
Synopsis
A marginal, off-shore flow existed early this morning. The surface pressure field, however, turned weakly on-shore toward the high desert by late morning. So, I expected areas near the coast would level off before getting warmer than normal. As it turned out (at least at UCLA), it wound up a little higher than I expected (73 degrees maximum on campus around noon).
The various computer models predict only minor changes tomorrow in the wind flow pattern (affecting southern California). Weak high pressure aloft should build over the region, but at the surface, increasing on-shore flow is predicted. Well inland areas may respond to the building high pressure by warming a little further (compared with what occurs today). Closer to the coast, things should be the same or even cool slightly over today’s highs (depending on subtle changes in the local, wind flow). I left my preliminary forecast numbers unchanged for Friday thinking that the sea breeze should be more “assertive” tomorrow.
On Saturday, an upper level trough to our west should approach. Several model solutions have consistently predicted showers reaching the Southland from this trough. It is predicted to be a little stronger than the trough that passed through the Southland on Tuesday (minor, measurable rain fell in some areas), and available water vapor should be sufficient for widespread wet weather. However, the predicted dynamics from this “storm” appear more favorable to the east and south of L.A. County (opposite case to the “storm” a couple days ago). I worded the campus forecast to indicate a “good chance” for showers late Saturday (based on model consensus), but confidence isn’t the greatest.
Even if the wet weather verifies, storm totals should be under a quarter inch in the lowlands away from the mountains. In L.A.County, I wouldn’t be surprised if totals stay well under a tenth inch (maybe just trace amounts being common). Snow levels may drop to 6000 feet for a time Saturday evening/Sunday morning, but little accumulation is anticipated (at best, 2-3 inches of “wet” snow). Atmospheric instability isn’t predicted to support thunderstorms.
Except for the early morning hours Sunday, most of that day should be just partly cloudy (parts of coastal plain may be sunny in the afternoon). The afternoon sea breeze should also blow briskly over most of the coastal plain. Despite the exiting “storm” on Sunday, a large scale troughing pattern along the West Coast is forecast by the numerical models. So, partly cloudy and cooler than normal weather should prevail for early next week. One trough embedded within the larger scale trough could produce some wet weather sometime in the Tuesday night- Wednesday period. At this time, a number of model solutions predict a relatively weak trough (weaker than this weekend’s system). The core of the trough may make landfall to our south. In short, chances of showers toward the middle of next week look remote (based on today’s model consensus).
Dry and warmer weather should occur for the last day of the month. It should last going into the first half of the subsequent weekend. A cooling cycle should begin after that. However, it may be a minor cool down, and some model solutions show a moderately strong high pressure aloft during the first full week of May (i.e. much warmer than normal weather). This is far from unanimous agreement though.
Next issued forecast/synopsis should be on Monday, 27 April.