| Day | Date | High/Low | Forecast |
| Thu | 14th | 69/54 | Sunny day and breezy at times. Mostly clear evening and breezy at times. |
| Fri | 15th | 69/53 | Mostly sunny day with scattered clouds; Possibly breezy at times in the morning. Scattered evening clouds. |
| Sat | 16th | 67/52 | Variable clouds but mostly sunny day. Variable evening clouds. |
| Sun | 17th | 67/52 | Mostly sunny day with some clouds. Becoming mostly clear in the evening. |
| Mon | 18th | 71/55 | Sunny day. Mostly clear evening. |
Synopsis
As the numerical models predicted, a moderately strong, Santa Ana wind event is in progress today (winds yesterday, while related, were more post “insider slider” winds). Peak wind gusts in the mountains exceeded 80 mph in a few locales this morning. The highest wind gusts I’ve seen were in the San Gabriel Mountains (86 mph at Magic Mountain Truck Trail) and San Bernardino Mountains (87 mph at Marshall Peak). The peak wind gust at UCLA is 34 mph (12:46 PM). The breezy weather (outright blustery in many areas) should continue through the evening, but upper air support for the strong, widespread winds should wane (compared with recent hours). The off-shore flow should weaken enough tomorrow to restrict winds to mainly higher elevations only . Although the off-shore flow isn’t predicted to completely end this weekend, significant wind should be in the mountains only.
As with most strong, Santa Ana wind events, daytime temperatures are often highest at or near the coast (related to influx of polar air and effects of warming by sinking air motion). Considering that it’s mid-March, warmest readings (so far) in the low 70s would make this a “cool” Santa Ana wind (would warm more commonly into the 80s). As the current influx of polar air (afternoon temperatures just in the upper 40s and 50s in the high desert) ends, somewhat warmer weather should prevail the next couple of days (exception might be immediate coast where a returning sea breeze should actually cool that area relative to today’s readings).
One can attribute the current Southland weather to a “cut-off” low pressure currently centered near Lake Havasu. While it’s generally clear in L.A. County, most of the Inland Empire and points south have been partly to mostly cloudy today. Radar has even detected showers with much of these clouds. However, with the off-shore flow producing a very dry, lower atmosphere (lowest 8000 feet or so), rain drops may not be reaching the ground in most locales (where radar indicates wet weather). The aforementioned, “cut-off” low is forecast to get as close as Imperial County tonight before it wobbles back to the Colorado River Valley tomorrow (northern Arizona by Saturday). The air mass to the south and east of L.A. County may get moist enough for some of those showers to produce measurable rain. Snow levels could fall to as low as 4000 feet in spots, assuming sufficient, evaporative cooling of the lower atmosphere takes place. The “cut-off” low pressure may even promote enough atmospheric instability to allow for isolated, short-lived, mountain thunderstorms.
Most of the wet weather threat should occur in the afternoon hours (tomorrow being the most active day though some showers are predicted over the weekend). Areal coverage should be confined mainly to the Inland Empire and points south (mountain and desert region). Some model forecasts include the eastern San Gabriel Mountains as well as the higher mountains in Ventura County (valid tomorrow afternoon). I wouldn’t rule this scenario out, but no relevant showers are likely in those locales. Also, unlike an event last Thursday, there shouldn’t be any showers migrating into the L.A. Basin (less instability predicted this time around as well as less favorable dynamics).
Today’s model consensus has the “cut-off” low pressure wavering somewhere near the California/Arizona border through Monday. However, it should also weaken throughout this period. So, it’s weather effects should become less noticeable with time. High pressure aloft should bring more warming early next week, but no widespread 80 degree weather (inland areas) is anticipated (high pressure not expected to be strong enough for that). By the middle of next week, marine layer weather should return to the coastal plain (typical for spring…astronomically speaking, spring arrives at 8:06 PM on Tuesday, the 19th. Looking farther out in time, some model solutions continue to show a minor storm threat over the subsequent weekend (occasional storms could follow the follow week). I still don’t have much confidence in any given scenario (some solutions favor high pressure and warmer then normal weather).
Next issued forecast/synopsis should be on Tuesday, 19 March.