A cooling trend continues through the weekend as highs fall to 10 to 20 degrees below normal. The marine layer will deepen onto the coastal mountain slopes with patchy drizzle and a slight chance of light showers for early Friday and a chance of showers for late Friday night through late Saturday night. The most likely time for showers is for Saturday afternoon along with a slight chance of thunderstorms for Orange and portions of southwestern San Bernardino Counties. There will be periods of stronger and gusty southwest to west winds for the mountains and deserts for Friday afternoon into Saturday evening with gusts to 45 to 55 mph along and below the desert slopes of the mountains. Quieter weather by Sunday with a drying and warming trend for next week with near or above normal high temperatures for inland areas beginning Tuesday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update: The latest high res models are indicating that there will be enough instability for there to be a few thunderstorms possible during the afternoon hours on Saturday, mainly for the San Bernardino Mountains and Inland Empire. Rainfall rates will generally be in the 0.10 to 0.20 range for the coastal and inland areas, and higher to around 0.30 for the western facing slopes, for locations in Orange County and northward, and lesser amounts for San Diego County. Locally higher amounts will be possible with any heavier showers/thunderstorms that develop. There will still be the possibility of some drizzle developing by later tonight through tomorrow morning as well, as the lower levels continue to become more saturated. Other than that, the forecast is still appearing to be on track, with drier conditions and a gradual warmup beginning Sunday through the middle of next week.
(Discussion submitted at 137 PM):
The marine layer cleared out of San Diego and Riverside counties this morning, and is now quickly burning off in Orange County. Clouds will continue to clear towards the coast through the afternoon before another, deeper, marine layer builds back in tonight. Heights continue to fall through Saturday as a trough off the coast of Canada becomes a cutoff low and sweeps down into California. Ahead of this low, gusty west winds develop across the mountains and deserts as the gradient tightens on Friday, extending into the evening. A Wind Advisory has been issued for Friday afternoon through late Saturday night, with gusts up to 45 mph in the deserts and up to 55 mph in the mountain passes. Areas of blowing dust will be possible both days, primarily in the deserts, with reduced visibility down to 3 miles or less in some spots. Further east, the deeper marine layer should be sufficient for some morning drizzle, heavy at times, especially in the valleys and up against the coastal slopes Friday morning. Moisture lingers as the low pushes into Central California Saturday morning, with some light rain/snow showers developing across the furthest north regions. Snow levels fall to around 4800ft by Saturday afternoon, and while the low looks to push south enough for some precipitation, any accumulations will be extremely light. Models continue to show some limited instability and isolated thunderstorms may develop late Saturday morning through early evening, primarily across the area stretching from the San Bernardino Mountains down into the IE and into Orange County. Any thunderstorms that manage to develop will bring gusty winds, and brief, heavy rain which could lead to some localized higher QPF amounts. Outside of any thunderstorms, QPF amounts will generally remain below 0.10" through all of Saturday.
As the low moves up into Nevada Sunday afternoon, any lingering precipitation and gusty winds will quickly end. Weak ridging begins to build back in over Southern California, with temperatures warming into early next week. Highs return to at or above normal by Tuesday, holding steady through late week as zonal flow aloft develops. At this point, models look fairly dry through at least mid week.
250330z. Coasts/Valleys/Coastal Mountain Slopes, Clouds based at 2500-3500 feet MSL with tops climbing to 5500 feet will gradually fill the entire coastal basin. Vis reduced 0-5SM in foothills. Patchy -DZ between 10-18Z Friday with accompanying lower cigs to 2000 feet MSL and lower vis 3-5SM. Clouds start to disperse 17-19Z Friday with some BKN clouds persisting far inland and in foothills. Clouds increasing again after 02Z Friday evening.
Mountains/deserts, Variable high clouds through Friday. West winds increase after 22Z Friday, gusting 35-45 kts, locally 50 kts, over ridges, through passes and desert slopes. Strong up/downdrafts are likely, with isolated LLWS and rotors in lee of mountains, such as vcnty KPSP.
No hazardous marine conditions are expected through Tuesday.
Ca, Wind Advisory from 2 PM Friday to 11 PM PDT Saturday for Apple and Lucerne Valleys-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
