A storm produced copious amounts of rain over much of northern California yesterday (heavy, "wet" snow on the highest peaks of the northern Sierras too). As expected, it pretty much fizzled by the time the storm reached southern California (plenty of available, water vapor but lacking storm dynamics). Still, rainfall turned out more widespread than I expected. The computer models indicated measurable rainfall barely reaching L.A. County, but it reached into the Inland Empire and south into San Diego County early today. Storm totals came in mostly as expected (under a tenth inch most areas, including 0.02 inch at UCLA), but I was surprised to see totals over a tenth in the Riverside County mountains (had expected only trace amounts at most).
The threat of wet weather is over in southern California despite considerable clouds in some areas as of midday. While daytime temperatures today are the lowest they've been this week (most areas), it's still mild for November (seasonable most locales). Sunnier weather is expected this weekend, and a weak off-shore flow will promote warmer than normal weather again. Even warmer weather is expected as Thanksgiving Day nears (more on that in a bit).
The aforementioned, off-shore flow should begin overnight tonight. The latest model runs have backed off further on any significant wind event (breezy weather in most Santa Ana wind prone areas but nothing too serious). Any breezy weather should diminish in areal coverage after tomorrow morning (only a brief period of wind support aloft...not that much to begin with, though). This off-shore flow event should be gone by Sunday afternoon (weak, on-shore flow for Monday). A new, off-shore flow should develop on Tuesday, but no widespread, significant wind should occur with this latter event. A surface, off-shore flow, however, could last through the Thanksgiving weekend.
Warmer than normal weather is likely this weekend, but the latest model runs have backed off slightly on how much warming may take place. 80 degree weather is probable, but temperatures in the coastal plain will probably stay under that. Areas near the coast may only see minor warming over today's readings (off-shore flow too weak to inhibit the daily sea breeze). A bit of cooling my occur on Monday as a storm affects northern California. The vast majority of model solutions keep wet weather well north of the Southland (plenty of mid/high clouds possible, however). In a worst case scenario, some sprinkles could get as far south as Ventura County Monday afternoon or evening.
While no widespread, significant, wind event is expected with next week's off-shore flow, it is almost certain to promote much warmer than normal weather (fairly strong high pressure aloft predicted). Widespread 80 degree weather is expected by Wednesday (campus included). Thanksgiving Day is currently expected to be the warmest day next week. There is potential for some isolated 90 degree readings. Cooler weather is expected for the remainder of the holiday weekend, but at this point, most model solutions favor only a slow cooling trend (temperatures above normal for the whole weekend). A few model solutions show a marine layer returning but not until the end of the holiday weekend.
Most of the longer range models keep the Southland dry for the remainder of the month (occasional wet weather for northern California but uncertain about areal coverage and amounts of precipitation). There are some model solutions depicting a minor rain threat reaching the Southland sometime after the 26th, but nothing shows up with any consistency (wet one run, dry the next few runs). Temperatures will probably run close to seasonable levels, but for now, it looks like no rain will fall in southern California for the rest of November.
UCLA Forecasts and analyses are written by James Murakami
– posted: 2017-11-17