High pressure aloft will slowly build in from the east this week, bringing gradual warming, a shallower marine layer, and mostly dry weather. For Thursday, temperatures will generally be about 3 to 7 degrees above normal. Shower and thunderstorm chances return for the mountains Thursday through Sunday with marginal cooling as the upper high shifts east and weakens.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This afternoon, Skies are mostly clear except for a few marine layer low clouds at the beaches. The marine layer remains about 1400 ft deep with a strong inversion. Temperatures are near to about 4 degrees warmer than at this time yesterday in the coastal areas, up to 6 degrees warmer in the inland valleys, 2 to 6 degrees warmer in the mountains and 2 to 4 degrees warmer in the deserts. High temperatures today will be in the 70s to low 80s near the coast, mid 80s to low 90s for the western valleys, mid to upper 90s in the Inland Empire, mid 70s to upper 80s in the mountains, mid 90s to low 100s in the high desert, and 105-110 in the low desert.
Numerical guidance is in good agreement through Friday with respect to the overall pattern, keeping SoCal sandwiched between high pressure to the east and a trough of low pressure to the northwest. There will be some minor differences in the forecast details but the trends should hold. We can expect gradual warming trend through Thursday when temperatures will be mostly 3-7 degrees above normal. By Wednesday, there is a 90-100% chance of at least moderate HeatRisk over the inland valleys, lower elevation mountains and deserts. Chances of major HeatRisk are around 10-30% over the far inland valleys, around 50% for the lower elevation parts of the high desert and 55-85% for the low desert. While high temperatures won't be significantly above normal, continued humidity and above normal overnight temperatures will contribute to the higher HeatRisk.The marine layer will slowly become shallower, with night and morning low clouds and fog restricted to the coastal areas for Wed-Fri.
The position of the high will bring more of a southerly flow aloft and an increase in deep-layer monsoonal moisture for Thu through the weekend. The added moisture will bring chances for afternoon/evening showers/tstms, mainly to the mountains but the potential is there for showers/tstms in the deserts as well.
After Friday, model solutions begin to diverge but overall it seems more likely than not that the high pressure will weaken a little as it is displaced farther east and south. The effects will be marginal at best, with high temperatures remaining near or up to 6 degrees above normal on Monday.
171800z. Coast, Intermittent low clouds along the beaches of SD county will begin to clear after 19-20Z, keeping SCT-FEW conditions at KSAN. Patchy low clouds to gradually increase overnight into Tuesday. Highest chance of cigs around 1000 feet MSL in San Diego County 12-16Z Tuesday, more isolated cloud coverage near KSNA. Clouds clear to the coast after 15Z Tue.
Otherwise, FEW-SCT high clouds AOA 15000 feet MSL increasing this evening, lingering into Tuesday. SCT-BKN clouds 10000 feet MSL over mountains 19-00Z.
Occasional northwest wind gusts will exceed 20 knots in the outer waters near San Clemente Island this afternoon and evening. Otherwise, no hazardous marine conditions are expected through Friday.
Ca, None. PZ, None.
