| Day | Date | High/Low | Forecast |
| Mon | 17th | 61/47 | Variable morning clouds; Becoming mostly cloudy in the afternoon and possibly breezy at times. Slight chance of light showers late afternoon. Clearing in the evening. |
| Tue | 18th | 64/49 | Mostly sunny day with some afternoon high clouds. Mostly clear evening. |
| Wed | 19th | 70/51 | Mostly sunny day with some high clouds. Some evening high clouds. |
| Thu | 20th | 68/51 | Mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Fri | 21st | 70/53 | Mostly sunny day with some high clouds. Mostly clear evening. |
Synopsis
A storm is passing through the state today. The southern end of the system is much weaker than the portion passing through northern California (only an average storm, however). Some light rain is falling in Ventura County as of 3 PM (a few spots reporting a hundredth or two inch of rain). With the main storm dynamics remaining well to the north, no widespread, relevant precipitation is expected as the cold front passes through. Depending on whether low level winds stay out of the west, there may or may not be widespread rain in the L.A. Basin (time period sometime 3:30 – 5 PM…less than half hour duration in any given spot away from the mountains). Measurable rain (less than a tenth inch) in L.A. County should be confined to near/over the higher mountains (coastal facing side at first). Snow levels may drop to as low as 3000 feet tonight (currently around 5500 feet), but by then, most activity should be winding down in the mountains (will take longer for areas to the east and south of L.A. County). Snowfall should be insignificant for most mountains.
Mostly sunny and warmer weather is expected for the remainder of the week. A brief, weak, off-shore flow should promote warmer than normal weather on Wednesday. A passing, upper level trough should favor a return of weak on-shore flow on Thursday. Another reversal may occur on Friday though any warming that day should be minor (no greater than what’s anticipated on Wednesday). Yet, another dip in temperatures should occur on Saturday (another passing trough to our north). Some of the computer models show a shallow marine layer setting up. If widespread low clouds develop in the coastal plain, Saturday temperatures should be lower than normal (less cooling in the valleys unless the marine layer turns out deeper than expected).
A more noticeable warm trend may occur Sunday and beyond (through at least next Tuesday). The model consensus show a moderate strength high pressure aloft and weak easterly wind flow closer to the surface (should dilute or purge Saturday’s marine layer). There is potential for the coastal plain to warm into the low/mid-80s early next week (some chance at isolated 90 degree weather next Tuesday in the coastal valleys). Any cooling trend (minor at first) shouldn’t occur till the second half of next week.
Last week, some of the longer range models predicted a minor storm reaching southern California around the 27th or 28th. While that scenario is still up for play, recent model runs have delayed any relevant threat of wet weather (in the Southland) by a few days (30th or 31st). It would be a minor storm (precipitation-wise), but temperatures in southern California would again be noticeably below normal (more like recent dry days). Of course, with the approach of spring (astronomically speaking, spring begins Thursday at 2:01 AM), model runs can vary quite a bit from day to day (wilder undulations in the jet stream more common by this time of year). So, I wouldn’t take the rain outlook too seriously for now.
Next issued forecast/synopsis may occur on Friday, 21 March.