Patchy fog over the coastal waters tonight. Strengthening east winds along the coastal slopes of the mountains and below the passes Wednesday with gusts to 45 mph and isolated gusts to 55 mph. East winds begin to weaken on Thursday. Mid and high clouds will spread into the area from the southeast Thursday into Friday with a slight chance of showers for the mountains late Thursday night. Well above normal temperatures through Thursday, followed by minor cooling Friday and Saturday. Warmer Sunday, then much cooler Monday and Tuesday with increasing chances of precipitation.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Offshore surface pressure gradients are trending stronger this evening, currently around -11.1 mb SAN-TPH and -3.9 mb SAN-DAG. Patchy low clouds continue over the coastal waters this evening, and could reach the beaches in spots early tonight (30-40% chance), then as east winds continue to strengthen any fog will be pushed offshore and dissipate.
Water vapor imagery is showing the Rex Block taking shape, with an upper level ridge of high pressure just off the coast of Central CA and an upper level low off the coast of Central Baja. The high will shift eastward over CA on Wednesday with the upper low to the south closing off, bringing easterly mid level flow aloft. This will provide some upper support to the offshore winds, which are still forecast to peak late Wednesday morning into Wednesday night with east winds gusting to around 45-55 mph along the coastal slopes, below the San Gorgonio Pass, and into the adjacent valleys. This pattern will also bring further warming on Wednesday, when highs will be well into the 80s west of the mountains and in the low deserts. The NBM has a 10-30% chance of high temperatures exceeding 90 degrees on Thursday along the I-15 corridor in San Diego County and over inland Orange County and far west portions of the Inland Empire. In general highs will be anywhere from 10-20 degrees above normal, approaching daily record values at numerous locations.
Previous discussion, y Thursday, the offshore flow weakens as the upper high gets displaced to the northeast in response to a low pressure trough moving in from the west, and the flow aloft becomes southeasterly. A cooling trend will begin, with high temps on Thu dropping into the 70s and low 80s west of the mtns. The circulation around the low to our southwest will draw some mid and high level moisture into SoCal, resulting in a slight chance of light showers over the San Diego County mtns for a few hours late Thu night.
The cooling trend will continue for Fri-Sat as the Rex block breaks down and an upper low moves over the region. Temps will still be 5-10 degrees above seasonal averages west of the mtns. This could also bring a return of onshore flow and marine layer low clouds/fog to the coastal areas.
A transient ridge will bring fair and warmer weather for Sunday before a more amplified low pressure trough again brings significant cooling, increasing clouds and chances for widespread precip next Mon-Tue. Forecast details for Mon-Tue remain uncertain, with a 25-45 percent chance of measurable precipitation for Tuesday. At that time, the snow level will likely be around 6,000 to 6,500 feet.
040430z, VFR and mostly clear skies through the period. Gusty easterly winds in the mountains increase after 16Z, with surface gusts up to 40-50 knots through mountain passes. Mod up/downdrafts near mtns, and localized LLWS in the Inland Empire possible 14-19Z. Localized BLDU possible for much of Wednesday, decreasing VIS down to 3SM at times.
No hazardous marine conditions are expected through Saturday.
Increasing northwesterly (270-280 degrees) long period (15-16 seconds) swell will bring elevated to high surf beginning Friday afternoon. Surf of 5-8 feet with locally higher sets will peak Saturday morning before slowly diminishing through Sunday. Impacts will be highest at west facing beaches, especially across San Diego County.
Ca, Wind Advisory from 4 AM Wednesday to 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.
