Building high pressure will bring a warming trend through Wednesday, with moderate to high HeatRisk for the deserts. Mid level moisture in southerly flow aloft will bring a slight chance of showers and thunderstorms this afternoon through Wednesday afternoon for the mountains of San Bernardino and Riverside Counties east and northeastward across the deserts of southern California. This will be followed by a cooling trend for Thursday through the weekend. Southwest to west winds will strengthen for Thursday through Saturday in the mountains and deserts, with gusts on Saturday of 30 to 40 mph locally to 65 mph in the northern Coachella Valley below the San Gorgonio Pass.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This afternoon, Mid-level moisture in southerly flow aloft is producing some high-based convective elements across the mtns and deserts of SoCal. This elevated convection could produce isolated dry lightning strikes and locally gusty winds. This could result in fire starts. See the Fire Weather discussion below.
The marine layer is about 2000-2500 ft deep with a strong inversion so some low clouds are persisting at the beaches. The moisture aloft could disrupt the radiation cooling tonight so low cloud coverage may be less tonight than last night. Temperatures are near or a few degrees lower west of the mtns than at this time yesterday while the mtns and deserts are generally warmer by as much as 10 degrees in a few locations.
High pressure building in from the southeast will continue the warming trend through Wednesday with a minor drop in daytime high temperatures on Thursday. High temperatures on Wednesday will range from a few degrees above average near the coast to 4 to 8 degrees above average inland. High temperatures on Wednesday will range from the lower to mid 70s near the coast to the 90s for the Inland Empire with 108 to 112 for the lower deserts. Tonight will be much warmer as well with low temperatures Wednesday morning mostly in the 80s for the lower deserts. The marine layer will remain around 2000 feet deep with night and morning coastal low clouds extending inland into portions of the western valleys late each night. The mid-level moisture will continue to move into SoCal from the south but the disturbance moving over us today will be mostly to our north by tomorrow and the high pressure will increase stability making deep convection less likely tomorrow.
A low pressure system moving southward out of the Gulf of AK will strengthen the onshore slow across southern California into the weekend. Southwest to west winds for the mountains and deserts during the afternoon and evening will strengthen for Thursday through Saturday, with gusts on Saturday of 30 to 40 mph locally to 65 mph in the northern Coachella Valley below the San Gorgonio Pass. The marine layer will deepen with night and morning coastal low clouds spreading farther into the valleys late each night.
The low pressure system will also bring a cooling trend through the weekend, with high temperatures on Sunday as much as 15 degrees below average for the mountains and inland valleys. High temperatures on Sunday will range from around 70 near the coast to mid 70s to lower 80s for the Inland Empire with the mid 90s to 102 for the lower deserts. High temperatures for next Monday and Tuesday will be marginally warmer.
230930z, Coast/Valleys, A stronger inversion has kept the clouds in place along the coast into the late morning, but all TAF sites should see CIGs (currently based around 1700-1900ft MSL) clearing out by 1900-1930z. Low clouds with bases closer to 1400-1600ft MSL begin to fill back in after 03z Wednesday. Given increased mid level moisture in place, the marine layer may be patchier in coverage than previous nights, and take longer to fill in to some areas. Clouds scatter back off the coasts around 18z Wednesday.
Mountains/Deserts, VFR conditions expected through the TAF period with periodic high clouds AOA 15000 ft MSL this afternoon/evening.
No hazardous marine conditions are expected through Sunday.
Surf will increase this afternoon with the arrival of a 3 foot 15 to 18 second period south swell from 190 to 210 degrees. Surf of 4 to 6 ft is expected through Thursday. Expect locally hazardous swimming conditions and strong rip currents through the week. Please see the Beach Hazards Statement for more details.
Ca, Beach Hazards Statement through Thursday evening for Orange County Coastal Areas-San Diego County Coastal Areas.
Red Flag Warning from 5 PM this afternoon to 11 AM PDT Wednesday for Victor Valley -Apple Valley -Lucerne Valley -Johnson Valley.
Extreme Heat Warning from 11 AM Wednesday to 8 PM PDT Thursday for San Diego County Deserts.
PZ, None.
