| Day | Date | High/Low | Forecast |
| Mon | 14th | 66/53 | Mostly sunny with variable high clouds after low clouds clear late morning. Return of evening low clouds likely. |
| Tue | 15th | 66/53 | Morning low clouds likely but mostly sunny with some high clouds by afternoon. Evening low clouds likely. |
| Wed | 16th | 65/53 | Morning low clouds; Partial afternoon clearing. Evening low clouds. |
| Thu | 17th | 65/53 | Mostly cloudy day but possible, partial afternoon clearing; Slight chance of morning drizzle. Cloudy evening with a slight chance of evening drizzle/light rain. |
| Fri | 18th | 65/52 | Mostly cloudy morning with a slight chance of light rain; Partly cloudy afternoon. Partly cloudy evening. |
Synopsis
A large but weak, upper level trough exists west of southern California. Smaller scale circulations embedded within the trough have made for a complex, wind flow pattern affecting the Southland. For the most, the effects aren’t significant in terms of sensible weather, but getting the weather details right is problematic (“one size fits all” doesn’t necessarily work). Thus, today’s forecast is based partly on what the computer model consensus shows plus some intuition on my part.
Day to day temperature changes this week may vary as much as a few degrees (today got briefly warmer than I anticipated…69 degrees). However, generally cooler than normal weather should prevail across the Southland, especially during the Thursday-Friday period. The various models predict a healthy depth marine layer for the work week (deepest should be Thursday-Friday). So, widespread low clouds west of the mountains should be a daily, weather staple (not necessarily as a widespread, solid overcast, however). Spotty, early morning mist/drizzle will be possible tomorrow and Wednesday. Varying amounts of mid/high clouds are also predicted at times.
By Wednesday evening, the aforementioned trough should trek eastward (reason for deepening marine layer). Some of the models show increased coverage of light rain by early Thursday. Most of the wet weather is expected to be adjacent to coastal facing foothills and mountains. Predicted, atmospheric instability doesn’t favor thunderstorm development on Thursday, but a stronger than currently predicted trough could change that idea. In any case, rainfall, where it occurs, shouldn’t amount to more than a tenth inch for most areas (quarter inch for a few spots adjacent to the mountains).
By Friday, a separate, cold trough from the north is forecast to absorb the other trough moving into the Southwest. It’s taking an “inside slider” path into the Southwest, but the cold trough should help trigger marine layer induced showers (best chances around mountains as well as areas to the east and south of L.A. County). Cold air instability isn’t forecast to be great, but brief-lived thunderstorms can’t be ruled out for Friday (east of L.A. County). Another tenth to quarter inch rain is possible for Friday. Snow levels on Thursday shouldn’t drop below 6500 feet, but it should briefly fall to 5000 feet early Friday. Possibly an inch of snow at resort level may occur (not widespread in areal coverage though).
Improving weather is expected over the weekend as the cold trough moves east away from the state. The marine layer isn’t forecast to go away (shallower and somewhat diluted). So, some areas of low clouds are probable for the morning hours (not necessarily as an overcast). Warming for the weekend should also be limited as no strong high pressure aloft is predicted to reach the Southland (temperatures near normal levels).
Most of the longer range models show a wind flow pattern that won’t allow for any significant high pressure to develop into the state. A mostly, on-shore flow pattern is foreseen for next week (near seasonable weather). Some models show high pressure building more securely in the last few days of the month, but it’s not a majority model solution for now (a few solutions even predict some wet weather reaching southern California).
Next issued forecast/synopsis may be on Friday, 18 April.