| Day | Date | High/Low | Forecast |
| Mon | 4th | 65/53 | Variable clouds but generally partly cloudy through the evening. Possibly breezy at times in the afternoon. Slight chance of light showers in the evening. |
| Tue | 5th | 67/54 | Partly cloudy morning but becoming mostly sunny by afternoon. Mostly clear evening. |
| Wed | 6th | 69/56 | Chance of morning low clouds; Otherwise, mostly sunny day. Mostly clear evening. |
| Thu | 7th | 73/57 | Chance of early morning low clouds; Otherwise, mostly sunny day. Mostly clear evening. |
| Fri | 8th | 76/58 | Sunny day. Mostly clear evening. |
Synopsis
A large, upper level low pressure (this one a “cut-off” type) was centered near San Luis Obispo early this afternoon. A band of light rain lay over a portion of northern California. In southern California, some weak instability showers were over some mountain areas (San Luis Obispo County southward into Santa Barbara/northwest Ventura Counties). This low pressure doesn’t possess much deep layered moisture (mainly marine layer driven in the Southland). Storm dynamics this far south is also rather weak. All the computer models predict additional showers over parts of the Southland through tomorrow. However, the primary threat (minor) for L.A. County should be tonight till the pre-dawn hours of Tuesday. No widespread, measurable rainfall is anticipated (best chances in the lowland County of a couple hundredths inch in the southeast). Based on the model consensus, a better chance of measurable rain (under a tenth inch in the lowlands away from the mountains) may be over parts of the Inland Empire southward into San Diego County. Isolated rainfall in the mountains could reach a quarter inch through tomorrow.
The upper low pressure center should reach the Colorado River by mid-afternoon tomorrow. The shower threat should wind down quickly after that time. It may be partly cloudy tomorrow morning in the L.A. County coastal plain, but I wouldn’t be surprised if good clearing occur by the afternoon (leaned today’s forecast that way). A brisk afternoon sea breeze is anticipated, but it should be less breezy tomorrow compared with today.
High pressure aloft will build into the state by Wednesday. Weakening on-shore flow should promote a diminishing marine layer. At this point, the model solutions aren’t predicting any full fledged, off-shore flow. A number of model solutions also maintain a shallow marine through the end of the week. A moderately strong high pressure aloft favors a good warming trend in the latter half of this week (lasting through early next week). However, a lingering marine layer may limit the warming cycle in the coastal plain (especially near the coast). Valley temperatures into the upper 80s to low 90s would be possible by the weekend. However, a shallow but defined marine layer could limit the campus area to the mid-70s. (low to mid-80s for a day or two, otherwise).
At one time, the longer range models showed a new upper trough forming over the state this Mother’s Day weekend. Now, only a minor, “inside slider” type trough is forecast. There may be a minor reversal or temporary halt to the late week, warming trend on Saturday, but widespread, warmer than normal weather is expected through early next week. A cooling trend is expected by the middle of next week, but for now, the model consensus shows only modest cooling next week (slightly warmer than normal). Most model solutions show no relevant rain threat in the state through mid-month.
Next issued forecast/synopsis should be on Thursday, 7 May.