Easterly Santa Ana winds will are peaking today along and below the coastal slopes of the mountains, with gusts to 45 mph and isolated gusts to 55 mph. The winds will continue into Thursday before weakening in the afternoon. A low pressure system off the northern Baja coast will direct mid and high level moisture and clouds into the area from the southeast Thursday into Friday with a slight chance of light showers late Thursday night into Friday. The weekend will be dry and a little warmer. Another low pressure system will approach the California coast next Tuesday and Wednesday, with cooling and increasing chances for precipitation. Confidence is low on the timing and amounts of any precipitation.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Sunny and warm this afternoon, with temperatures 5-25 degrees higher in the coastal areas and valleys than at this time yesterday while the mtns are about the same. Surface pressure gradients remain offshore, with -12.1 mb SAN-TPH and -5.9 mb SAN- DAG. The wind-prone locations are still reporting easterly winds gusting 35-45 mph with local gusts up to 60 mph within the last hour.
From previous discussion, The Rex Block is in place, with an upper level low about 300 miles off the coast of central Baja and an upper high centered over western NV. The resulting easterly flow over SoCal will continue to enhance the offshore winds at the sfc. As a result, the Santa Ana winds will continue to strengthen today into tonight before beginning to weaken on Thursday as the Rex Block breaks down, the offshore pressure gradients weaken and the flow aloft becomes southeasterly.
Temperatures will trend lower for Thu and Fri but will remain about 10-15 degrees above seasonal averages in the coastal areas and inland valleys. High temperatures on Thursday will range from the lower to mid 70s near the coast to the mid 70s to lower 80s for the valleys and inland Orange County. The coast and valleys will cool around 5 to 10 degrees on Friday with Friday high temperatures ranging from the mid to upper 60s near the coast to the upper 60s to mid 70s for the valleys.
The low pressure system off the northern Baja coast will draw mid and higher level subtropical moisture into the area from the southeast on Thursday into Friday. This will result in a slight chance of showers for late Thursday night into Friday. Showers will be mostly confined to the mountains. If any showers develop west of the mtns or lower deserts, precip is unlikely to reach the ground do to a deep and dry sub-cloud layer. Friday will likely be the coolest day, with daily high temps in the 60s and 70s west of the mtns. Some high-resolution models are also indicating the return of marine layer low clouds and fog to the coastal areas Thu night/Fri morning.
Temperatures will trend higher for the weekend, with Sunday high temperatures as much as 8 to 12 degrees above average for the valleys and lower coastal slopes of the mountains. High temperatures on Sunday will range from around 70 near the coast to the 70s to around 80 for the valleys and inland Orange County with the lower deserts in the lower to mid 80s. Onshore flow will continue into Sat, spreading marine layer low clouds and fog farther inland.
For next Mon-Wed, A more amplified low pressure trough will move in from the west bringing more significant cooling, increasing clouds and chances for widespread precipitation, mainly over and west of the mountains. Forecast details remain very uncertain due to the spread among model solutions. The National Blend of Models indicates a 50-70 percent chance for measurable precipitation over and west of the mtns for Tue-Wed, and a 25-35 percent chance for 0.25 inch or more.
042130z, Mostly clear skies and VFR conditions will continue into Thursday afternoon. Gusty northerly to easterly winds have picked up today across the foothills, mountain passes, and into inland valleys this afternoon, with surface gusts observed ranging from 40-55+kt near mountain passes and 20-30 kts stretching into in the inland valleys. Moderate up/downdrafts in lee (west of) mountains. Pockets of BLDU sporadically reducing vis 3-5SM in parts of the inland valleys. Localized instances of LLWS may spread westward to the coasts, especially where offshore winds do not surface with onshore winds at the surface.
A building westerly swell (out of 280 degrees) may bring seas of 7-9 feet in the outer waters near/around San Clemente Island. Otherwise, no hazardous marine conditions are expected through Monday.
Increasing long-period (15-16 second) swell from the west-northwest (280 degrees) will bring elevated to high surf of 5-8 feet with locally higher sets late Friday into Saturday. Impacts will be greatest at west facing beaches, especially across southern San Diego County.
Ca, Wind Advisory until noon PST Thursday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.
PZ, None.
