A low pressure system moving southward off the California coast will spreading cooling inland through Thursday. It is expected to bring showers and slight chance of thunderstorms for late Wednesday through Thursday is it moves inland through California into Nevada. 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 Thursday), The center of a closed low pressure system will move southward off the California coast today, then move slowly eastward to near Point Conception for early Thursday, then northeastward into Nevada for Thursday evening. Cooling of high temperatures will continue to spread inland for today and Wednesday. The greatest cooling is expected on Thursday with the mountains and inland valleys around 10 degrees cooler than Wednesday.
High temperatures on Thursday will range from around 5 degrees below average near the coast to 15 to 20 degrees below average for mountain elevations above 6000 feet. High temperatures on Thursday will be in the 60s to around 70 for the coast and valleys and in the 40s and 50s for the mountains.
Satellite imagery and surface reports show coastal low clouds beginning to spread inland, but with cloud bases around 1000 feet near the coast as the marine layer deepens. Through sunrise this morning, the low clouds will increase in coverage for coastal areas and spread into the far western valleys. The low clouds are expected to spread into the far inland valleys or lower coastal slopes of the mountains for late tonight as the marine layer continues to deepen for today and tonight.
Moisture being drawn northward by the low pressure system off the California coast could bring some mostly light showers to the mountains for this afternoon and early evening, mainly for the San Bernardino Mountains and for the Riverside County mountains.
As that low pressure system off the California coast begins to move slowly eastward on Wednesday, showers could spread into coastal areas during the afternoon on Wednesday. Those showers are expected to spread farther inland for Wednesday night into Thursday with the greatest chances for thunderstorms for late Wednesday night into Thursday.
Through Thursday night, rainfall across Orange and southwestern San Bernardino Counties could range from around 1 inch near the coast to 1.5 to 2 inches in the mountains. Rainfall for San Diego County will range from around 1 inch north to 0.50 to 0.75 south. High desert areas will receive around 0.50 inch of rainfall with 0.25 inch or less for the lower deserts.
NBM probabilities for 0.10 inch or more of rainfall from Wednesday morning through Thursday night exceed 90 percent for the coast, valleys, and mountains. Probabilities for 0.50 inch or more exceed 80 percent from the coast to the mountains as far south as the northern half of San Diego County. Probabilities for 1 inch or more exceed 50 percent from the coast to the mountains for Orange and southwestern San Bernardino Counties. Probabilities for 2 inches or more exceed 10 percent from inland Orange County to the mountains of southwestern San Bernardino County.
(Friday through Monday), Warming and drying is expected for the weekend into early next week with some weak offshore winds possible during the weekend. For Saturday through Monday, high temperatures for coastal areas will range from 5 to locally 10 degrees above average with inland areas around 5 degrees below average to locally 10 degrees below average in the mountains. High temperatures for the coast and valleys will be mostly in the mid 70s to lower 80s with the lower deserts in the lower to mid 80s with the mountains in the 50s and 60s.
201130z, Coast/Valleys, Areas of intermittent low clouds based around 1200-1800 feet MSL extending into western valleys through 16Z. Low clouds based around 1800-2200 feet MSL to redevelop after 05Z tonight, extending into parts of inland valleys by early Wednesday. Vis reduced 2-5SM inland.
Otherwise, mostly clear and VFR conditions through 18Z. SCT-BKN clouds based around 10 kft develop over inland areas, especially mountains, 19-01Z. Isold SHRA over mountains 21-01Z. Random SCT clouds thereafter.
A storm system will move through the coastal waters late Wednesday through Thursday. Southerly winds Wednesday and Wednesday night will shift to westerly then northwest Thursday, with isolated and occasional wind gusts exceeding 20 knots. There is a 10-20% chance of TSRA Wednesday night through Thursday. No additional hazardous marine conditions are expected Thursday night through Saturday.
Southerly swells will continue to bring surf of 3 to 5 feet with sets to 6 feet, highest at south and southwest-facing beaches today. 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. Details are in the Beach Hazards Statement.
Ca, Beach Hazards Statement through this evening for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
