FXUS66 KSGX 191122 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 422 AM PDT Fri Jul 19 2024 .SYNOPSIS... High pressure over the southwest states and Great Basin will bring a more stable and slightly drier atmosphere through the weekend with very hot days and very warm nights for inland areas. Moderate to major heat risk is expected in the valleys and mountains with major to extreme heat risk for the deserts. A return of greater monsoonal moisture will bring more humid conditions for the early and middle part of next week along with a chance for afternoon early evening showers and thunderstorms for the mountains and deserts. Night and morning coastal low clouds will continue to spread into the western valleys at times late each night. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Sunday)... High pressure over the southwest states and Great Basin will bring a more stable and slightly drier atmosphere through the weekend with high temperatures for the coast and valleys likely peaking on Saturday with high temperatures on Sunday a few degrees lower. The higher Heat Risk through the weekend into next week will continue to be driven more by the very warm overnight temperatures for inland areas than by the very hot daytime temperatures. The heat is most likely not going to be record setting in terms of high temperatures. However some record warm low temperatures are more likely to be tied or broken for the mountains and deserts with the most likely day on Saturday. Aside from the heat, night and morning coastal low clouds will continue to spread into the western valleys at times late each night. && .LONG TERM (Monday through Thursday)... Greater monsoonal moisture will return early next week with increasing chances for afternoon and early evening showers and thunderstorms for the mountains and deserts. NBM has the greatest chances for measurable rainfall on Tuesday at 28 percent for Big Bear. While the Heat Risk for inland areas may decrease slightly for Monday through Thursday from this weekend, surface dewpoints increase early next week with heat index/apparent temperature values for the deserts, valleys, and mountains higher than for Friday through this weekend. There likely won't be any real relief from the heat much before the final weekend in July as cooling and drying occurs late next week from a trough of low pressure along the West Coast. && .AVIATION... 191000Z...Coast/Valleys...BKN-OVC low clouds near 600-1200 ft MSL will continue to blanket coastal and far western valleys this morning, with higher terrain obscured in clouds/fog. Confidence is high that cigs will clear coastal TAF sites 17-19Z today. Confidence lowers on timing of low clouds tonight, with latest thinking after 07Z tonight. Similar bases are expected as well. Mountains/Deserts...ISO TSRA will occur on Friday afternoon across the mountains. CB bases around 10000 ft MSL and tops to 40000 ft MSL. Areas in and near storm activity will be accompanied by local VIS reductions in +RA, gusty winds, and locally strong UDDFS. Otherwise, occasional SCT-BKN clouds at/above 10000 ft MSL will prevail through this evening, clearing overnight. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 11 AM this morning to 9 PM PDT Sunday for Riverside County Mountains-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-San Diego County Valleys. Excessive Heat Warning from 11 AM Saturday to 9 PM PDT Sunday for Apple and Lucerne Valleys. Excessive Heat Warning from 11 AM this morning to 9 PM PDT Sunday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC...17 AVIATION/MARINE...APR