Cooler and dry this weekend. Patchy fog along the coastal areas and coastal mesas tonight. Weak to locally moderate Santa Ana winds develop Monday and weaken Tuesday with warmer and drier weather. 20-35% chance of light precipitation Wednesday into Thursday, though confidence remains very low. Another round of offshore winds like follow this system for the late week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today through Monday,
In response to a shortwave trough now swinging through the Great Plains, a 1026mb surface high in Nevada is contributing to a weak offshore gradient, with north/easterly winds only felt in the deserts to the mountain passes. Elsewhere, onshore flow prevails though a meager coastal eddy this morning failed to reestablish marine clouds, providing another cool morning across the coastal basin. Aside from some high clouds, mostly sunny skies today warms temperatures up to seasonable norms for late November.
The next shortwave trough is set to dig from the Pac NW through the Great Basin tonight into Sunday, bringing elevated onshore winds Sunday afternoon, mainly for the higher elevations in the mountains and adjacent desert slopes. Wind gusts near 25-35 mph expected in the high deserts/desert slopes with upwards of 35-45 mph near mountain peaks. The marine layer will likely be less patchy tonight, with cloud cover stretching into portions of the western inland valleys. As cold air spills into the Great Basin behind this upper trough, the offshore pressure gradient is expected to strengthen on Monday, more than what is seen today. This Santa Ana wind event looks to be weak to moderate strength with strongest wind gusts Monday afternoon found in and just below Cajon/Banning Pass and Fremont Canyon up to 45-50 mph, with 25-35 mph gusts spreading into the Inland Empire and inland Valleys of San Diego and Orange Counties. As for temperatures, Sunday will likely be a few degrees cooler than today with the onshore flow, followed by warming and drying on Monday with the offshore flow.
Tuesday into Late Week,
Onshore flow is quickly reestablished Tuesday afternoon, moderating temperatures back to average. Beyond Tuesday, the upper level pattern remains quite uncertain through mid-late week as models continue to disagree on the evolution of the next trough, set to dig southward on Wednesday. The GFS and its ensembles have a weaker, shallower, and faster trough, while the ECMWF and its ensembles feature a deeper and slower system. While this disagreement persists, confidence on any precipitation, both timing and amounts, will be low. In a scenario like the GFS's, precipitation amounts will be very low, likely 0.1" or less, with northerly offshore flow building Wednesday into Thursday. If the ECMWF's solution were to verify, precipitation amounts could be closer to 0.25-0.5+" with rain chances stretching into Thursday, delaying northerly offshore flow into late Thursday into Friday. Uncertainty in snow levels exists as well, but will generally be falling to around 6500-6000ft Wed-Thurs. Either way, this storm system isn't expected to be an efficient rain maker, but stay tuned over the next few days to see how this evolves. Still, temperatures are likely to cool below average Wed-Thurs with the trough/cloud cover, though with the potential for offshore flow, its a bit too early to say for sure.
292030z. Coasts/Valleys, Very patchy low clouds with bases around 400-700ft MSL will develop and move ashore after 02Z Sunday with VIS down to 1-4SM. VIS may fall to 1/2SM or lower earlier in the night for obscured coastal terrain. A weak eddy may allow bases to rise a bit, possibly to around 600-1200ft MSL by 10-13z. Clouds will begin to clear back towards the coast by 15-16z.
.Mountains/Deserts, VFR conditions expected through the TAF period. Strong surface winds exceeding 30 mph at times possible in the deserts and eastern mountain slopes generally after 16z Sunday. Mod up/downdrafts expected in the vicinity of the mountains and for any low-flying aircraft.
No hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
