Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
377 FXUS66 KSGX 110427 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 927 PM PDT Wed Jul 10 2024 .SYNOPSIS... Hot conditions will continue into Thursday before a gradual decrease in temperatures Friday through the weekend. Areas of fog and low clouds will persist along the coast reaching into the western valleys overnight, with locally dense fog in portions of the valleys by Friday morning. There are chances of showers and thunderstorms in the mountains, locally into the deserts, Saturday and Sunday afternoon and early evening. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Visible satellite at 9 PM was showing widespread low clouds along the coast. Low clouds and fog will reach into portions of the western valleys overnight. Areas of locally dense fog are possible overnight and early Thursday morning, especially in valley locations and on coastal mesas. Hot conditions are expected Thursday with continued widespread moderate to major heat risk for most areas away from the coast with extreme heat risk in the mountains and deserts. Today was the 20th consecutive day of Palm Springs reaching of 110F or higher. The record number of days is 27, set in July 1959. There is the potential for Palm Springs to reach 120F Thursday with only a shallow local moisture surge reaching into the deserts and dewpoints reaching the 60s. The ridge of high pressure aloft will move east Friday through the weekend, resulting in decreasing temperatures this weekend into early next week. From Previous Discussion Issued 2 PM July 10, 2024 Upper trough on the backside of the main ridge will slide up the West Coast Friday and Saturday which enhances the southeast flow aloft and moisture increases across Socal in mid levels leading to isolated diurnal thunderstorms over the mountains and desert slopes. The best chance for surface based convection is over the weekend with very marginal chance in highest peaks on Friday in late day with sea breeze and upslope flow peaking. An upper low riding on the west side of the upper high will draw tropical moisture northward but may not entrain enough for elevated convection. Precipitable water rises to around 1.5 inches in the deserts during the weekend. Upper high builds back into Socal next week, in traditional fashion over southern Nevada and the 4-corners region. Slight warming trend inland or stable and little above seasonal warm averages. && .AVIATION... 110400Z...Coast/Valleys...Satellite shows the marine layer rebuilding along the coast. BKN-OVC with 600-1000 feet MSL will continue to push inland tonight, with tops right around 1200-1400 feet MSL. Around 11/06z-11/07z, lowering VIS to 2-4 miles and bases around 300-400 feet MSL likely for coastal sites, continuing through around 11/16z. Localized areas of VIS around or below a mile possible in the valleys tonight through Thursday morning. Similar to Wednesday afternoon, a slow retreat of the marine layer is expected on Thursday, with scattering out at coastal airports around 11/19z- 11/21z before redeveloping around 12/02z with similar bases and tops. Mountains/Deserts...Mainly VFR with SKC through the period. Localized VIS reductions down to 3SM due to smoke in the vicinity of the San Bernardino Mountains from the Vista fire. Winds generally light, but periods of gusty northwesterly winds possible up to 30kts around San Gorgonio Pass through Thursday evening. && .MARINE... No hazardous marine conditions are expected through Sunday. && .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...CO AVIATION/MARINE...Zuber