Cooler west of the mountains today as onshore flow returns but warmer inland away from the marine layer influence. A low pressure system moving into California brings cooler and breezy conditions Monday through the middle of the week, along with a slight chance of precipitation Tuesday afternoon into Wednesday morning. Cool weather and breezy onshore flow persist into next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This afternoon, high clouds are streaming over the region in southwest flow ahead of a weak upper level disturbance embedded in the cyclonic flow around an extensive low pressure system southeast of the Gulf of Alaska. The patchy low clouds in the coastal areas and valleys from this morning have dissipated. Temperatures are mostly a little higher than at this time yesterday except at low elevations west of the mountains where onshore flow is spreading the cooler maritime air inland. High temperatures today will be near or a few degrees above seasonal averages.
The low pressure system south of the Gulf of AK will move inland across CA through Wednesday, with the closed upper low well to our north. This will bring widespread cooling with strengthening onshore flow producing gusty southwest to west winds, mainly in the mountains and deserts where gusts of 45-50 mph will likely occur late Tue into early Wed. Height falls aloft ahead of the approaching low will enable the marine layer to deepen tonight into Monday morning, with increasing low clouds spreading farther into the inland valleys.
SoCal will be on the southern periphery of the low pressure system, with limited moisture available for precipitation. Any precipitation is likely to fall between late Tuesday and early Wednesday. Current precipitation estimates are for a trace to a few hundredths of an inch in the valleys and coastal areas, although many locations will get no precipitation. The coastal slopes of the San Bernardino Mountains could get about 0.15 inch of precipitation. The snow level will fall to about 6500-7000 ft on Wed morning but any significant snow accumulations is unlikely.
This system will also bring strong and gusty southwest to west winds to the mtns and deserts. The winds will be strongest between Tue afternoon and Wed morning when gusts of 45-50 mph, locally to 55 mph, are expected in the mtn passes and on adjacent desert slopes.
The upper level trough axis will move east on Wed morning and the winds will begin to weaken while colder air filters in from the northwest. Wednesday will likely be the coolest day with high temperatures near or a few degrees below normal in the coastal areas and low deserts while in the mountains, temperatures could be as much as 12 degrees below normal.
SoCal will remain under the influence of broad upper level troughing for the latter half of the week into next weekend. We can expect temperatures near or a little below seasonal averages with a deep marine layer and onshore flow producing breezy conditions in the mtns and deserts.
191800z, SCT upper level clouds based around 20k ft will gradually move out of the region today.
Coast/Valleys, Low clouds 1100-1600 ft MSL will form offshore after about 03Z Mon, gradually moving inland through the evening. Clouds may initially be patchy, with hole in cig cover. Cigs will lift slightly and move further inland overnight, with a 30% chance for impacts vcnty KONT/KSBD after 12Z. Low clouds clear 15-17Z Mon, with increasing high level clouds afterwards.
Mountains/Deserts, Increasing westerly to southwesterly winds across the desert slopes into the deserts this afternoon/evening, with gusts to 20-30 kts. Otherwise, VFR conditions expected through the TAF period.
No hazardous marine conditions are expected through Tuesday. Elevated onshore (northwesterly) wind gusts near 20-25 knots are possible Wednesday afternoon into early Thursday morning, which would bring elevated, choppy seas. Another, briefer round of gusts to around 20 knots Thursday afternoon and evening would be more localized to the far outer waters near San Clemente Island.
Ca, None. PZ, None.
