Temperatures remain below normal into Wednesday with a present marine layer. Warmer weather returns for the end of next week as high pressure builds.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
The 00z sounding Friday afternoon shows a well mixed marine boundary layer, around 3000 feet deep. Low clouds will be patchy overnight through the coastal basin and scatter out to the coast between 8-11 AM this morning.
While the coastal basin will maintain modest minimum relative humidity values (30-60% inland, 60-80% coast) this afternoon, conditions will be very dry for higher mountain communities and eastward into the deserts, dropping to 8-15%. These low daytime humidities improve for mountains/deserts through Monday afternoon with more typical minimum RH values down to 15-30%.
The closed upper low over Idaho continues to trek eastward and is being replaced by a shortwave ridge, bumping up our temperatures this afternoon by 3-6 degrees relative to yesterday. The ridge moves out of the region quickly as another closed low approaches from the west Sunday, centering over Central California by Monday. Temperatures once again drop to 6-12 degrees below average across inland areas Monday as the marine layer deepens and low clouds fill the coastal basin during the nights and early mornings of early next week.
The upper closed low weakens and combines with the main jet stream in the Northern Rockies, leaving behind very weak higher pressure anomalies over the eastern Great Basin and thus perhaps a very weak N/E low level offshore pressure gradient Wednesday (~20% chance). The extent of the effects would be limited to how dry the air would be through the deserts and mountains and thus how much the daytime temperatures could spike for inland later in the week. With the trough already moving out, temperatures are already forecast to jump up 5-10 degrees into Wednesday with highs later in the week (including Wednesday) reaching back into the low-100s in the low deserts, mid-90s in the IE, mid/upper 80s inland and around 80 for coastal areas. These are all temperatures typical for mid-September, though maybe a few degrees above average at the coast.
Beyond, WPC model clusters are converging on solutions showing another trough developing off of the west coast by next weekend. The amplitude and intensity of this trough are uncertain, and there is thus uncertainty about whether temperatures stay near average or dip below average again.
191130z, Coast/Valleys, Low clouds based 2000-3000ft MSL will be intermittent for parts of the Inland Empire and Orange County this morning. Low to moderate confidence on cigs covering KONT and KSNA this morning between 13-16Z. Clearing from valleys to coast 16-18Z. Cigs slightly lower 1500-2500 ft MSL tonight into Sunday morning. Low clouds pushing ashore 02-04Z Sunday with lower confidence on cigs covering areas of the Inland Empire after 12Z Sun.
Mountains/Deserts, Mostly clear and VFR conditions through the weekend.
No hazardous marine conditions are expected through Wednesday.
Ca, None. PZ, None.
