Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
612 FXUS66 KSGX 100437 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 937 PM PDT Tue Jul 9 2024 .SYNOPSIS... The hottest days for the coast and valleys will be through Thursday with not much change for the mountains and deserts. An influx of monsoonal moisture over the weekend could bring a slight chance of afternoon and early evening showers and thunderstorms for the mountains and deserts. A gradual slow cooling trend will begin around Friday and continue into next week, with high temperatures on Monday within a few degrees of average. Night and morning coastal low clouds will spread into portions of the western valleys at times late each night. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This evening... Marine layer low clouds returned relatively early to the immediate coast and have already spread 5+ miles inland. Today was another hot day inland with three climate locations setting new daily Max temp records. Through Thursday... The ridge of high pressure responsible for this heat wave will continue to slowly shift eastward through this week. Temperatures will continue to remain well above average through the next two days as the ridge axis slowly moves into Arizona by Thursday. Temperatures are expected to be 10 to 15 degrees higher than seasonal averages and new temperature records remain possible through this time period. A shallow marine layer will continue to moderate temperatures within a few miles of the coast as low clouds return each night. Friday through Monday... A weak upper level low pressure system will disrupt the current pattern beginning late Thursday. This low pressure system will remain nearly stationary off the California coast through the rest of the week but its presence will displace the dome of high pressure to the east and bring southerly flow aloft, allowing some increased moisture to be advected over the area. This monsoonal like increase in moisture will lead to a decrease in temperatures beginning Friday along with increasing the chances of showers and thunderstorms this weekend. The best chances for thunderstorms will likely be over the higher terrain of the mountains, nearby deserts, and other locations where convergence allows for early storm initiation. The marine layer will continue to moderate heating near the coast through the long and short term period, with marine layer stratus clouds moving back inland late each evening before dissipating in the morning hours. && .AVIATION... 090245Z...Coast and Valleys...SCT-BKN low clouds with bases 500-1000 feet MSL currently along the coast will move into portions of the western valleys through 13Z. VIS 2-4 miles in BR will occur in the far western valleys through 16Z Wed. SCT conditions expected for inland areas 16-18Z Wed. Cigs could locally linger at beaches into Wed afternoon, most likely in San Diego County. Mountains/Deserts...Clear skies with unrestricted visibility expected for most areas through Wed. Areas of FU will continue in the San Bernardino county mtns and the High Desert from the Vista fire. West winds with gusts 20 knots expected 22Z Wed-12Z Thu through mountain passes. This will lead to weak up/downdrafts over and east of the mountains. && .MARINE... No hazardous marine conditions are expected through Saturday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning until 9 PM PDT Thursday for San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Mountains-San Diego County Valleys. Heat Advisory until 9 PM PDT Thursday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-Santa Ana Mountains and Foothills. Excessive Heat Warning until 9 PM PDT Friday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts- San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC...PG AVIATION/MARINE...CO