Cooling conditions and increased westerly winds on the desert mountain slopes into the deserts tomorrow into Thursday. The marine layer will deepen into Thursday, spreading low clouds and fog into the valleys. Periods of northeasterly Santa Ana winds and warmer conditions this weekend, with less marine layer low clouds and fog. Moisture from the east could bring some showers for Sunday and Monday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update: The forecast in the short term continues to remain on track with the trough passing to the north tomorrow, which will allow for gusty winds to pick up by later in the afternoon, especially across the higher terrain. For this reason, there is a Wind Advisory in place. In terms of the forecast beyond into the weekend and early next week, there appears to be growing confidence that there will be an upper level low moving down to the south of the region, which may allow for a few showers to develop over the mountains on Sunday afternoon, and maybe into Monday as well. Temperatures will remain around the seasonal average through the middle of next week, with with only minor fluctuations.
Previous discussion submitted at 340 PM:
Visible satellite at 11 AM was showing mostly clear skies over land, with marine layer low clouds well offshore. Weak transient ridging will build over Southern California today, bumping temperatures 3 to 7 degrees warmer than yesterday west of the mountains. In the deserts, temperatures are forecast to be similar to a degree or two cooler than yesterday. The upper level ridging will be short lived, as an upper level low pressure system moves into the Pacific Northwest Wednesday into Thursday, pushing the ridge east.
The approaching low will begin to spread cooling inland Wednesday with high temperatures for the coast and valleys a few degrees cooler than today. Much greater cooling will spread inland on Thursday with high temperatures 10 to locally 15 degrees cooler for the deserts onto the desert slopes of the mountains. In addition to cooler conditions west to northwest winds will increase over the desert mountain slopes and locally into the deserts Wednesday night into Thursday. Current forecast has gusts mainly 45 to 55 mph with isolated gusts to 65 mph. Winds will weaken and quickly turn northerly by Thursday afternoon. Mostly weak Santa Ana winds are expected on Friday. By Saturday the low that brought us the gusty onshore winds is expected to break off from the mean flow and retrograde to our southwest, strengthening the offshore pressure gradient. Ensemble guidance is currently showing the strongest north to northeasterly winds on Saturday, with a slight weakening into Sunday. For Saturday there is a 90 percent chance of weak Santa Ana winds, 70 percent chance of weak to locally moderate winds, and a 40 percent chance of moderate strength winds. For Sunday, chances of weak winds is the same, with a 45 percent chance of weak to locally moderate winds, and a 20 percent chance of moderate winds. Both days have a 5 percent or less chance of moderate to locally strong winds.
With the low positioned to the southwest on Sunday night, it will have the opportunity to entrain moisture. This will at least bring enough moisture the area to increase cloud coverage. There is some potential enough moisture may be present to produce some showers. Current forecast for Sunday and Monday follows the NBM with a slight chance of showers, with highest chances over the San Diego county mountains. By Sunday, 58 percent of ensemble clusters are showing the low in a position (to our southwest and off the coast of Baja) to bring precipitation over parts of Southern California with a similar output for Monday. The rest of the solutions are drier with the low further east over the Baja Peninsula.
Highs on Friday will warm the most at the coast, with minimal change or cooler conditions expected in the deserts due to the cold air advection from the Great Basin. A warming trend will continue through the weekend, with the most noticeable warming at the coast due to the prevailing offshore flow. The offshore flow will also keep marine layer low clouds and fog from developing.
040600z. Coast/ western valleys, VFR persists through early this evening with low clouds will begin making their way in along the SD County coast after 06Z, filling into the valleys by 09Z and will spread north over the Orange County coast 11-12Z. Bases will be around 1,000-2,000 ft MSL, dropping to 200-700 ft MSL with vis 3-5SM 10-14Z at coastal sites. There will be partial clearing from the
Everywhere else, VFR conditions with some high clouds AOA 25,000 ft MSL.
Stronger northwest winds will return late Wednesday and last into Thursday, producing choppy conditions that may become hazardous. Otherwise, no hazardous marine conditions are expected through Saturday. A Small Craft Advisory is in effect, which contains more details on this.
Ca, Wind Advisory from 10 PM Wednesday to 10 AM PST Thursday for Apple and Lucerne Valleys-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.
PZ, Small Craft Advisory from 10 PM Wednesday to 10 AM PST Thursday for Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.
