A warming trend continues through Wednesday, with high temperatures as much as 10-15 degrees above seasonal averages in the valleys. Weak to moderate Santa Ana winds will develop for Tuesday through Thursday, with the strongest winds expected on Wednesday. Minor cooling on Thanksgiving with highs remaining well above normal, followed by more significant cooling Friday through early next week. A trough of low pressure will bring a chance of showers for the weekend into early next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This afternoon, Variable high clouds cover much of the region with hazy sunshine while patchy low clouds remain over the coastal waters. Temperatures are near or a little lower than at this time yesterday in the coastal areas and inland valleys. In the mtns and deserts, temps are a little higher.
The high pressure ridge over the eastern Pacific will continue to build over the west coast, keeping the marine layer very shallow and continuing a warming trend through Wednesday. At the same time, a sfc high moves into the Great Basin setting up offshore pressure gradients which will produce Santa Ana winds across SoCal. Northeast to east winds will begin to develop early Tuesday, strengthening into Wednesday then weakening on Thursday. The winds will be strongest on Wed and a lack of upper level support means that the strongest winds will be mostly restricted to the passes, canyons and coastal foothills. In these wind-prone areas, we can expect wind gusts of around 35-45 mph on Wednesday. The upper level ridge and the Santa Ana winds will combine to bring significantly warmer and drier conditions especially west of the mtns.
Patches of low clouds and fog will likely return to the coastal areas tonight but the developing offshore flow could cause it to clear out before sunrise tomorrow.
Wednesday will likely be the warmest day with daytime high temperatures 10-15 degrees above seasonal averages in the inland valleys and 5-10 degrees above seasonal averages elsewhere. Temperatures will lower a little on Thanksgiving (but will remain several degrees above seasonal averages) as the the upper level ridge begins to weaken and shift east.
A vigorous shortwave trough moving inland to the north on Friday will usher in a pattern change which will see a return of low pressure troughing over the western states. This will bring a cooling trend and a return of onshore flow for Friday into early next week. While the longwave pattern is likely to result in broad troughing over the western US, the timing and trajectory of low pressure systems embedded in this pattern are highly uncertain due to the spread among model solutions. As a result, confidence in forecast details is not high.
Since the last model run, the number of ensemble members indicating precip for next Sun-Mon is increasing so confidence is growing that another round of rainfall/snow is on the way. For now, precip estimates are still very uncertain but indications are that the system producing the rain/snow will be colder so snow levels could fall to 5000 ft or lower. Daytime temperatures in the valleys and coastal areas could be as low as the upper 50s for next Sunday.
242100z, Coasts/Valleys, SCT-BKN patchy low clouds based 700-1000 ft MSL coastal waters. Patchy low clouds 500-800 ft MSL redevelop after Tue 04Z within about 10 miles of the coast, with vis 3-6 SM along coastal areas and 1-2 SM over higher coastal terrain (30-40% chance for vis 1/4-1/2 SM over elevated coastal terrain). Similar to this morning, expecting clouds to be in and out of sites.
Mountains/Deserts, VFR conditions expected through tonight. NE winds locally gusting to 25 kts.
No hazardous marine conditions are expected through Friday.
Ca, None. PZ, None.
