FXUS66 KSGX 051618 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 918 AM PDT Mon Aug 5 2024 .SYNOPSIS... Not much change in the heat or moisture for inland areas today with a less than 10 percent chance for an isolated shower or thunderstorm in the mountains. Monsoonal moisture will increase for Tuesday and Wednesday with a 10 to 20 percent for isolated thunderstorms on Tuesday afternoon and a 15 to 25 percent chance for isolated to scattered thunderstorms on Wednesday afternoon. Monsoonal moisture may decrease slightly for Thursday and Friday with a less than 10 percent chance for afternoon thunderstorms, then increase for next weekend with a 10 to 20 percent chance for afternoon thunderstorms for the mountains and deserts. Patchy night and morning low clouds and fog will continue along the coast. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Morning Update... Low clouds and fog are dissolving near the coast this morning, where John Wayne Airport in Orange County reported visibility near 1/4 mile very briefly. The peak of the heat can be expected today with highs near 5 to 10 degrees above normal. There is a 50-70% and a 30-50% percent chance of seeing highs over 95 today in east county San Diego and inland portions of Orange County respectfully today. Moderate to high chances of temps over 115 today are expected in northern parts of the Coachella Valley and the Anza- Borrego desert. Most areas will remain dry today, but latest hi- res guidance depicts a storm may pop up across higher terrain, best chance near the Mexican border in the mountains. Heat alerts remain in effect through Tuesday as a cooling pattern will take hold with increasing monsoonal moisture by Tuesday and Wednesday. Small mountain/desert storm chances with warm weather continue into later this week with a shallow marine layer near the coast, which will lead to low clouds and patchy fog each night and morning. .Previous Discussion (416 AM Today)... .SHORT TERM (Today through Wednesday)... Not much change in the heat or the monsoonal moisture for inland areas for today with a less than 10 percent chance for an isolated shower or thunderstorm for the mountains this afternoon. Monsoonal moisture will increase for Tuesday and again on Wednesday with high temperatures on Tuesday slightly cooler and on Wednesday a few degrees cooler near the coast to around 5 degrees cooler for the mountains, inland valleys, and lower deserts. With the increase in monsoonal moisture, there is a 10 to 20 percent for isolated thunderstorms on Tuesday afternoon for the mountains and deserts and a 15 to 25 percent chance for isolated to scattered thunderstorms on Wednesday afternoon. Patchy night and morning low clouds over the coastal waters will extend locally inland near the coast late each night. && .LONG TERM (Thursday through Sunday)... There will be slight drying of monsoonal moisture for Thursday and Friday with a 10 percent chance or less for an isolated shower or thunderstorms for the mountains each afternoon. Then another slight increase for next weekend with a 10 to 20 percent chance for afternoon showers and thunderstorms for the mountains and deserts. ECMWF ensemble output then shows a steady decrease in precipitable water values for next week. High temperatures for the middle of the week will not be quite as hot with the increase in monsoonal moisture. Then warming for the coast and valleys going into next weekend, but with next weekend not as hot as this past weekend. && .AVIATION... 051525Z...Coast...FEW low clouds with bases 600-800 ft MSL along portions of the coast, mainly KCRQ southward this morning. Tops around 1500 feet MSL. A FEW-SCT high cloud AOA 20000 ft MSL. After about 12Z tonight FEW low clouds with bases 600-800 ft MSL along portions of the coast with FEW-SCT high cloud AOA 20000 ft MSL. Low clouds are expected to become BKN-OVC and more widespread along the coast through 15Z Tue with bases 400-800 ft MSL. Moderate confidence in cigs impacting coastal TAF sites through 15Z. Localized VIS reductions to 0-3SM for higher coastal terrain and valleys through 15z. SCT high clouds AOA 20000 ft MSL and unrestricted VIS expected after 15Z. Moderate confidence in cig redeveloping at coastal TAF sites after 12Z Tue, with bases under 1000 ft MSL. Valleys/Mountains/Deserts...SCT clouds AOA 20000 ft MSL with unrestricted VIS into Tue AM. Near the mountains, Cu may develop 19Z Mon-00Z Tue with bases near 12,000ft MSL. && .MARINE... Breezy northwest winds with gusts 15-20 kt expected in the outer waters this afternoon and evening. Otherwise, no hazardous marine Areas of FEW-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 11 PM PDT Tuesday for Apple and Lucerne Valleys-Coachella Valley-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Deserts-San Gorgonio Pass Near Banning. Heat Advisory until 11 PM PDT Tuesday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Diego County Mountains-San Diego County Valleys-Santa Ana Mountains and Foothills. PZ...None. && $$ PUBLIC...APR/17 AVIATION/MARINE...Small