Cooler with night and morning low clouds in the coastal areas and valleys tonight. A low pressure system moving southward along the West Coast will bring stronger onshore winds Monday into Tuesday night, along with showers from the coast to the mountains Monday night into Tuesday night. Gradual warming and drying with periods of weak offshore flow Wednesday through Friday. For next weekend the warming continues inland while marine layer clouds and fog return to the coastal areas.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Satellite imagery indicates that marine layer clouds have scattered out of the coasts and western valleys. Expecting clear skies along with cool and breezy conditions today under a broad trough covering the western CONUS. Marine layer deepens further tonight into Monday as a shortwave begins to plunge southward along the US west coast. Highs 5 to 15 degrees below normal Monday with increasing west to southwest winds.
By late Monday, the tightening gradient ahead of the approaching shortwave will lead to elevated to strong wind gusts for the mountains and deserts. Winds peaking late Monday night with widespread gusts 30-40 mph and exceeding 55 mph for the wind- prone passes and slopes. This system will also bring colder air, and chances for showers and high-elevation snow. Tuesday will likely be the coldest day with daytime temperatures as much as 10-20 degrees below normal in the inland valleys, mountains and deserts. Precipitation will begin Monday night into early Tuesday morning, starting in the northern and western areas (vicinity LA basin) and spreading south and east through the day on Tuesday before ending Tuesday night. Rainfall guidance has trended upward slightly due to the track of the low shifting slightly west which allows for more marine influence. Rainfall rates may exceed 0.25" per hour for the northwestern coastal basin in OC and the western Inland Empire. Higher rates possible for coastal slopes of the Santa Anas and San Bernardino County Mountains. Rainfall amounts will range from 1 to 2 inches along the coastal slopes of the San Bernardino County Mountains to almost nothing in the lower deserts. Generally higher amounts expected in the northern and western areas with 0.25-0.75" for lower elevations of OC and the Inland Empire. Generally less than 0.25" in the vicinity of San Diego. Snow levels will remain generally above 7000 feet with minor accumulations above resort levels. Big Bear Lake may see a dusting.
Much more benign weather expected from Wednesday onward with a gradual return to seasonably cool temperatures by late week. A weak offshore surface pressure gradient may inhibit marine layer clouds from reclaiming the coastal basin for a few days. By the weekend, a weak ridge should be in place along with continued seasonably cool temperatures. From there, solutions diverge notably but there is some indication that another upper low pressure system may affect the west coast early next week.
121530z. Coasts/Valleys, BKN low clouds based near 1500 ft MSL will begin to clear most of the region by 17-18Z. Mostly clear this afternoon with low clouds based near 1500-2000 ft MSL reforming over coastal areas after 05Z Mon, mostly in San Diego County. Clouds becoming more widespread into OC and southern IE after 08Z, including VCTY RIV/RBK. Lower confidence in cigs reaching VCTY KONT/KSBD 17-20Z Mon. CIGs will rise overnight through Mon morning across the region between 2500-3500 ft MSL.
Mountains/Deserts, VFR conditions expected through the TAF period. Gusty W/SW winds desert facing slopes of the mountains into the deserts after 18Z Mon. Wind gusts 20-40 kts will create MOD UDDFS.
No hazardous marine conditions are expected through Monday, though winds will be breezier than average out of the southwest Monday afternoon. A weather system approaches the area Tuesday, with increasing winds out of the south to southwest. Increasing confidence on winds of 20-25 knots and choppy seas for all areas Tuesday morning through the evening.
Ca, None. PZ, None.
