Today was the hottest day of the week so far but a cooling trend is expected for Tuesday through Thursday. Night and morning low clouds and fog will be present each day through the forecast period along the coast and into portions of the valleys. A gradual warming expected for the end of the week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today was the warmest day of the week so far with a couple of locations in San Diego County setting records (see the RERSGX product). Many locations in the inland valleys reached temperatures in the upper 90s, and in the low deserts, temperatures reached as high as 111 degrees at Indio. This evening, the marine layer is a little lower than last night but onshore flow has already pushed low clouds a few miles inland in coastal San Diego County.
From previous discussion, High temperatures Tuesday for inland locations will fall 6 to 12 degrees from their peak today as a shortwave trough weakens and pushes the upper level ridge to our east.
Guidance is in good agreement that a weak troughing pattern will prevail over the US West Coast Tuesday through Thursday. This will maintain marine layer low clouds and fog for the coast and valleys and take high temperatures back to within a few degrees of normal. For Friday and Saturday, the majority of ensemble clusters keep the upper level pattern high-zonal, which will bring a few degrees of warming to the area. Highs are forecast to be 5 to 10 degrees above average.
By Sunday most ensemble clusters indicate the return of weak troughing which has the potential to cool conditions a few degrees. There still remains some uncertainty in the temperature forecast for early next week. The current forecast follows the deterministic NBM which continues to be more in line with the warmer end of most other ensemble guidance.
120400z, Coast/Valleys, Low clouds based 700-1200 ft are pushing inland, eventually covering all of the Orange County lowlands and reaching to the inland valleys of SD Co. by 08z. VIS reduced to 0- 3SM for inland valleys with patchy fog and 3-6SM with BR for elevated coastal areas (200-600 ft MSL elevation). There is moderate confidence that bases will rise above 1000 ft MSL at some point early Tuesday morning, starting sometime between 09-14z. Around a 70% chance cigs reach into the Inland Empire, 11-16z, bringing patchy IFR cigs/vis. Bases continue to lift (and VIS improves) throughout the morning to 1500-2500 ft MSL but are only likely to scatter out inland 18-21z. Within 10 miles of the coast, cigs are expected to remain patchy through the afternoon. Cigs based 1500- 2500 ft MSL develop quickly after 01z Wed, reaching 20 miles inland by around 04z Wed. There is good confidence for VIS reductions below 3SM and fog along foothill slopes, otherwise, lower confidence for VIS reductions below 3SM for eastern inland valleys and Inland Empire valleys.
Otherwise, SKC and VFR through Tuesday evening.
No hazardous marine conditions are expected through Saturday .
Ca, None. PZ, None.
