An area of low pressure will move over the region through Tuesday, accompanied by continued cool and cloudy weather. Gusty west winds in the mountains and deserts with a chance for showers for the coastal basin will occur this evening through Tuesday afternoon. High pressure will move into the region bringing a warming trend with drier weather for the remainder of the week, along with increased heat risk for inland valleys and deserts.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This evening, A moist boundary layer about 8,000 ft deep with a deep dry layer above is bringing widespread clouds from the mountains to the coast. Embedded in this cloud mass are isolated to scattered light showers moving from southwest to northeast in the cyclonic flow around a closed upper low just north of Point Conception. Mostly light showers will continue at times through much of the day Tuesday.
From previous discussion, Winds out of the west continue to be breezy across mountain passes into the deserts locally near 25-45 MPH. We can expect these winds to weaken into Tuesday morning then strengthen again Tuesday afternoon/evening. The center of the low pressure system will move inland this evening into Tuesday, where light to moderate showers will expand from the coastal slopes to the beaches. Hi-res model guidance favors San Diego County to see the best chance for light rainfall overnight into Tuesday morning, while parts of Orange County and the Inland Empire may see nothing. Most areas will see under one tenth of an inch. Some showers may produce rates of about one quarter inch/hour in the heaviest rain, leading to totals near one half inch possible; best chance in the San Diego valleys and foothills.
Chilly temperatures will remain through Tuesday with this system as highs stay in the 60s west of the mountains/high desert and 70s for the lower deserts. Tuesday and Wednesday mornings will be cold across the mountains with temperatures in the 20s and 30s. Big Bear will dip near 25 degrees; the daily record lows for both Tuesday and Wednesday being 21 degrees, so not too far off!
The weather system moves out of the region Wednesday. This will be the one day where temperatures will be near seasonal averages. High pressure off the coast will quickly grow and expand by Thursday into the end of the week, accompanied by much warmer weather. This will lead to highs about 10 degrees above normal away from the coast to start. 70s and 80s will dominate the coast and valley regions of Orange and San Diego Counties. High temperatures will near 100 degrees on Thursday across the lower deserts with high confidence in reaching this value by Friday. Model guidance diverges some on the exact strength and placement of the high, so the temperature forecast becomes hot for May standards by the weekend into early next week, but just how hot? We'll continue to work out these details, but please be prepared for moderate to locally high heat risk to impact inland valleys and across the desert regions.
050400z. Coast/Valleys, SCT-BKN layered low clouds based between 2500-5000ft MSL will continue tonight before rising to 3-6 kft after 15z Tue; partial scatter out at times during the day after 17z closer to the coast, remaining BKN-OVC inland. ISO -SHRA over coastal areas to become more numerous in coverage over SD County after 06z before tapering off after 17z (through 22z over the inland foothills). More isolated SHRA activity north of SD County, through 12z. MVFR vis/cigs in SHRA. There is some uncertainty regarding cigs Tuesday evening; guidance is suggesting cigs will remain only along eastern valley foothills, clearing slowly elsewhere.
.Mountains/Deserts, Strong westerly gusts up to 25-35 kts with isolated gusts of 45 kts are expected to continue this evening and overnight, weakening slightly after 12z. Winds pick up again slightly Tuesday afternoon after 00z. This will create moderate to strong up/down drafts and local LLWS in the lee of mountains. Expect reduced vis in BLDU in deserts areas. Coast-facing mountain slopes will occasionally be obscured between 3000-6000 feet MSL in BR where clouds intersect terrain.
No hazardous marine conditions are expected through Friday.
Ca, None. PZ, None.
