A cooling trend begins today as a low pressure system approaches from the northwest. A deepening marine layer could bring patchy drizzle to portions of the coastal areas and inland valleys this morning. The system will move inland through Tuesday bringing lower temperatures, breezy conditions and chances of light rain showers for Monday and Tuesday, mainly over and west of the mountains. Dry and warmer for Wednesday into next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This morning, the marine layer is about 2000 ft deep with low clouds covering most of the coastal areas and portions of the inland valleys. The deepening marine layer could bring patchy drizzle this morning west of the mountains. Widespread high clouds are moving east across the region ahead of a low pressure system approaching from the northwest.
This low pressure system will move inland through Tuesday, with the closed upper low moving over central and southern CA. The system will bring stronger onshore flow, lower temperatures and periods of mostly light showers over and west of the mountains. Southwest to west winds will steadily strengthen through today, peaking this afternoon/evening then weakening a little on Monday morning before strengthening again Monday afternoon/evening. Winds will be strongest late Monday with gusts of 35 to 45 mph and isolated gusts to 60 mph in the mountain passes and adjacent desert areas. Winds will weaken on Tuesday. Monday and Tuesday will be the coolest days this week, with daytime high temperatures in the 60s west of the mtns and in the high deserts (2-12 degrees below normal), in the 40s-50s in the mountains (10-20 degrees below normal), and in the 70s to near 80 in the low deserts (up to 15 degrees below normal). High-resolution models indicate that the first wave of isolated to scattered light showers could move through the region tonight followed by a relative dry period Monday then a second wave of showers will move through Monday night/Tue morning. By Tue afternoon, the showers will have moved east leaving behind mostly cloudy skies. Precipitation totals will favor San Diego County and the coastal mountain slopes while the deserts remain largely rain-shadowed. Totals will range from a trace in the coastal areas and valleys to about one quarter inch in the San Diego County mtns.
Dry and warmer weather will follow for Wed into next weekend with some day-to-day variations in the marine layer presence as a ridge of high pressure builds over the west coast. Daytime high temperatures could be 10-15 degrees above normal in the inland valleys, mtns and deserts.
030930z. Coast/Valleys, Low clouds based 1400-2000 ft MSL are covering inland areas up to the foothills in SD/Orange Counties, filtering in gradually into the IE (Inland Empire). VIS reductions 2-6SM in interior valleys (e.g. KRNM) and parts of the IE (0-4SM in the southern IE). Full low cloud coverage is anticipated through the IE by sunrise; over 50% chance for cigs reaching KSBD by 12z. Spotty -DZ possible in coastal areas, 12-16z. VIS improves gradually in the valleys after 14z as bases rise through the morning to 2000-3000 ft MSL by 15-17z. Scatter out 17-19z in the IE. Only partial scatter out for inland valleys and 60-80% chance cigs remain through the afternoon over Orange County and SD. County west of I-15. Cloud bases in the afternoon 2000-3000 ft MSL and continue to rise Sunday evening and night. Clouds fill back into interior valleys by 22z Sunday afternoon and fill the rest of the coastal basin by 06z Mon. Slight chance (15-25%) for -RA/DZ throughout the coastal basin after 04z Sunday night.
.Mountains/Deserts, VFR conditions expected through the period with SCT-BKN high clouds AOA 20 kft. Winds strengthen along desert slopes and into deserts starting after 21z Sun. Widespread gusts 25-35 kts expected Sunday evening and overnight, locally reaching 45-50 kts along desert slopes and through mountain passes.
No hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
