Widespread precipitation across the lower deserts and adjacent mountain slopes through this morning with showers occasionally making it west of the mountains. Snow levels will rise from 6500 to 7000 ft today. Showers tapering off this afternoon into tonight, with dry conditions expected to return by Sunday. Periods of gusty northeast to east winds will continue through this evening. A gradual warming is expected for next week, with high temperatures returning to above normal by the middle of the week. A weak Santa Ana is possible sometime mid-week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Current radar as of 830 AM shows widespread light precipitation east of the Peninsular range. Some light rain has made it over the mountains, drifting westward through the Inland Empire and through the San Diego County valleys toward the coast.
Orographically forced snow showers continue for the eastern slopes of the San Bernardino and Riverside County mountains above 7,000 feet. Breezy snow showers along with patchy fog above 5,000 feet are causing reduced visibilities for many east facing mountain areas. High resolution guidance continues to show most of the rain and snow shower activity wrapping up and moving eastward by noon with only a slight chance for any given area to experience a stray shower through the afternoon hours.
Northeast and east winds continue to gusts to 35-50 mph along west facing foothills and mountain slopes, expecting to weaken around 4PM.
Otherwise, drier and calmer weather expected for Sunday.
Previous discussion issued 230 AM November 22,
The upper level low is currently centered off the coast of northern Baja and will begin its eastward progression as a vort max rounds the base of the low. Another vort max is lifting north on the eastern side of the low, and as a result widespread light precipitation has developed over the deserts with a few light showers also wrapping around from the north. Light showers will occasionally drift west of the mountains today, but for the most part the bulk of the precipitation is forecast to occur over the deserts and adjacent mountain slopes. Rainfall accumulations in these areas will range from around 0.10-0.40 inch, with isolated amounts closer to 0.80 inch on the east slopes of the Laguna Mountains. West of the mountains any additional accumulation will be less than 0.10 inch. Snow levels are still hovering around 6500 ft, but will rise to 7000 ft later this morning. Additional snow accumulations of a few tenths to around 2 inches is expected, locally higher on the east side Onyx Peak and Mt San Gorgonio.
Showers will gradually taper off this afternoon into tonight as the low moves eastward, ending by early Sunday morning. Northeast to east flow around the north side of the low and offshore pressure gradients will cause breezy winds to continue across the coastal mountain slopes and below the passes with local gusts up to 45 mph in the wind prone areas this morning. Winds weaken this afternoon as gradients and mid-level flow weaken.
Once the low moves out, an upper level ridge will move in from the west and amplify into midweek, bringing a warming trend. Surface high pressure building in over the Great Basin behind a pair of weak short waves will drive a round of true Santa Ana winds Tuesday through Thanksgiving, causing additional warming west of the mountains where high temperatures will be around 5 to 10 degrees above normal on Thanksgiving. Cw3e West-WRF now has a 40% chance of weak to moderate Santa Ana Winds on Tuesday and Thursday, and a peak of around 55% on Wednesday. There is a 15% chance of a moderate event on Wednesday. Given the lack of any upper level support, winds will generally be confined to the usual passes/canyons and coastal slopes.
Beyond Thursday, ensembles are struggling with the breakdown of the ridge and an upper level trough approaching. In general, Friday should be cooler with a return of onshore flow. The timing and track of the next upper trough is still all over the place, some showing a lower amplitude trough, potentially as an inside slider which would lower precip chances here, others digging the low further south with a slower track which would result in higher precipitation chances/amounts but delayed a day or so. For now forecast follows NBM PoPs which brings a slight chance in beginning Saturday morning, increasing to around a 20-30% chance Saturday night.
221630z, Coasts/Valleys, Currently, patchy -RA occurring in valleys and and areas eastward, favoring eastern facing mountain slopes and adjacent deserts. FEW-SCT bases 5-7 kft MSL and an OVC layer based 8- 10 kft MSL. FG to reduce vis 0-2 SM above 5000 ft MSL and SNSH to reduce vis 0-5SM above 7000 ft, especially along east facing slopes. -RA/SNSH taper off after 20z along with vis improvements in the mountains. In the afternoon, only a slight (20%) chance for a leftover ISO SHRA/SNSH for any given area. East to northeast winds gusting 25-35 knots in the coastal foothills and locally into valleys through about 00z Sunday.
No hazardous marine conditions are expected through Wednesday.
Ca, Winter Storm Warning until 10 AM PST this morning for Riverside County Mountains-San Bernardino County Mountains.
PZ, None.
