Through Sunday, stronger onshore flow and a weak coastal eddy will bring gradual deepening of the marine layer with cooling spreading inland. Night and morning coastal low clouds and fog will increase in coverage and spreading a little farther inland each night through the weekend. Weak northerly flow on Monday will bring warming for the coast and valleys and cooling inland. A low pressure system moving southward along the West Coast will bring cooling for Wednesday and Thursday. If the track is far enough to the west, there would also be a chance of showers.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Morning Update,
Very low marine layer clouds that brought brief dense fog conditions to extreme northwestern Orange County this morning have pushed out to sea, and the Dense Fog Advisory that was in effect has been allowed to expire. Otherwise, mostly clear skies expected today with no other changes to the forecast. See the previous discussion for more details about the upcoming forecast.
From previous discussion,
(today through Sunday), A weak coastal eddy has developed with local higher-resolution model guidance showing the eddy continuing into Sunday morning with slow deepening of the marine layer along with increasing coverage of night and morning coastal low clouds and fog.
The lower level flow is still weakly offshore, though trending weakly onshore. Satellite imagery shows low clouds and fog over the coastal waters remaining off the coast of San Diego and southern Orange Counties and drifting farther off the coast with the low clouds and fog extending locally inland into northern Orange County and southern Los Angeles Counties. The fog is locally dense with visibility of one-quarter mile or less at Long Beach and Los Alamitos.
As onshore flow returns and the marine layer slowly deepens, cooling will spread inland through the weekend. High temperatures today for the coast and valleys will be as much as 4 to 8 degrees cooler than Thanksgiving with the greater cooling on Saturday for the mountains and high desert. The cooling will continue for the coast and valleys on Sunday as the marine layer deepens. High temperatures on Sunday will be a few degrees below average for coastal areas with the mountains and deserts as much as 4 to 8 degrees above average. High temperatures on Sunday will range from the lower to mid 60s near the coast to around 70 for the valleys with the 70s for the lower deserts.
(Monday through Thursday), For Monday, northerly low level flow will bring cooling of 4 to 8 degrees for the mountains and high desert and warming of a few degrees for the coast and valleys. The coast and valleys will cool a few degrees on Tuesday and the mountains and high deserts will warm a few degrees as the lower-level northerly flow weakens.
For Wednesday and Thursday, a low pressure system moving southward in the vicinity of the West Coast will bring cooling. Depending on the track and evolution of this system, it could also bring a chance of precipitation.
281600z. Coasts/Valleys, Low clouds based around 400-700ft MSL have been hanging just offshore, unlikely to impact any TAF sites this morning. Low clouds have a better chance to move ashore tonight (45-60% chance) after 02z Sat with bases slightly higher than this morning, 700-1200ft MSL. Clouds will push 5-10 miles inland. Localized VIS reductions down to 4-6SM, with 1-3SM for elevated coastal terrain. Any low clouds should begin clearing to the coast around 16-17Z.
.Mountains/Deserts, VFR conditions expected through the TAF period.
No hazardous marine conditions are expected through Wednesday.
Ca, None. PZ, None.
