Onshore flow will begin to spread cooling inland today with a return of coastal low clouds and fog more likely for tonight into Tuesday morning. A low pressure system from the north is expected to bring greater cooling for Wednesday and Thursday along with showers and a chance of thunderstorms, most likely for Wednesday night through Thursday afternoon. Then warmer and drier for next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
(today through Wednesday), High temperatures for today will be slightly warmer for the mountains, deserts, and inland valleys with coastal areas into the western valleys a few degrees cooler. Greater cooling will spread inland on Tuesday and Wednesday with Wednesday high temperatures near average at the coast to 5 to 10 degrees below average for the mountains. High temperatures on Wednesday will be mostly in the 70s for the coast and valleys and in the mid 80s for the lower deserts.
Satellite imagery shows some patchy low clouds and fog off the Orange County coast beneath a strong and shallow marine inversion. There could be some very patchy dense fog near the Orange County coast early this morning. The more likely time for a return of greater coverage of low clouds and locally dense fog for the coastal waters into coastal areas is for tonight into Tuesday morning. Deepening of the marine layer and greater inland spread of coastal low clouds into portions of the valleys is expected for Tuesday night into Wednesday morning.
A closed low pressure system centered to the west of Point Conception on late Tuesday will begin to move slowly toward the east on Wednesday. This will draw subtropical moisture and showers northward ahead of this low pressure system on Wednesday. Showers will begin to move into portions of southwestern California during the day on Wednesday.
(Wednesday night through Sunday), That low pressure system will move slowly eastward and inland into southern California for Wednesday night and Thursday. This will bring showers and a chance of thunderstorms to southwestern California, most likely for Wednesday night through Thursday afternoon.
The ECMWF Extreme Forecast Index has rainfall across coastal portions of Orange and Los Angeles Counties in the 80th to 90th percentile. Cold air aloft with the low pressure system passing over near record warm water off the coast will increase the instability with the ECMWF Extreme Forecast Index having CAPE over the coastal waters into coastal waters in the 80th to 90th percentile and locally in the 90th to 95th percentile.
For Orange and southwestern San Bernardino Counties, rainfall could range from around 1 inch for the Orange County coastal plain to around 1.5 inches on the coastal slopes of the mountains with amounts decreasing from north to south across San Diego County.
High temperatures will be coolest on Thursday, as much as 15 to 20 degrees below average for the mountains. High temperatures on Thursday will be mostly in the 60s to around 70 for the coast and valleys and mostly in the 40s and 50s for the mountains.
Drier and warmer weather is expected for next weekend, but with growing spread in just how much warming for Saturday through Monday. HeatRisk is forecast to remain below Moderate for next weekend.
191700z, Coast, VFR and SKC through late this evening. Low clouds and fog much more likely to form after 05Z Tuesday, becoming more widespread by 12Z Tuesday. Bases would be around 500-800 feet MSL with vis 1-6SM on mesas and higher coastal terrain initially, with bases and vis likely rising slightly Tue morning before clouds scatter out 16-17Z.
Otherwise, Mostly clear and VFR conditions except for SCT-BKN cumulus based around 10 kft over mountains 19-00Z.
No hazardous marine conditions are expected through Wednesday morning. A storm system moves into the region later Wednesday through Thursday, bringing gusts at or exceeding 20 knots and associated choppy seas, along with a 10-15% chance of TSRA.
Southerly swells will continue to bring surf of 3 to 6 feet with local sets to 7 feet, highest at south and southwest-facing beaches through Tuesday. This will bring hazardous swimming conditions for most. While surf and rip currents will be elevated, daily high tides will not be particularly high, and the threat of coastal flooding is minimal. Further details can be found in the Beach Hazards Statement.
Ca, Beach Hazards Statement through Tuesday evening for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
