Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
740 FXUS66 KSGX 101623 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 923 AM PDT Wed Jul 10 2024 .SYNOPSIS... The upper ridge is over southern California and slowly shifting to the east. This will result in the hottest inland temperatures today and Thursday with a slow decrease late week and into the weekend. The southerly flow behind the upper high will begin to draw in tropical moisture Friday which continues into Sunday. Fog and low clouds will persist along the coast due to the strong inversion under the warm air mass increasing inland on Friday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Lower marine layer this morning due to the slightly warmer air mass over Socal. This has resulted in fog along the coast. The top of the layer is near 1400 feet MSL and inland penetration is less but clouds are extensive. The clouds will clear but hold at the beach due to strong inversion. With the recent heat wave ocean beach temperatures have risen to around 70F. Under the ridge the air mass is 28-33C at 850 mb today and Thursday holding the slightly lower marine layer inversion but air mass will lower 1 to 2C Friday through Sunday in the cooling and deeper marine layer trend. Palm Springs has now had 19 consecutive days of 110F or higher. The record is 27. The 120F fulling mixing potential exists for today and Thursday with only shallow local moisture in the desert giving the dewpoints in the 60s. 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 Sunday. For the upper low tropical moisture may not entrain enough for elevated convection. Precipitable water rises to around 1.5 inches in the deserts. Upper high builds back into Socal next week, in traditional fashion over southern Nevada and the 4-corners region. Slight warming trend inland. && .AVIATION... 101603Z...Coast/Valleys...BKN-OVC clouds with bases 600-1000 ft MSL and tops to 1200 ft MSL will continue within 15-25 miles of the coast through 16Z-19Z Wed, with higher terrain locally obscured. Local VIS 1-3 miles will occur over higher coastal terrain through 16Z Wed. Low clouds will locally linger near the coast Wed afternoon and slowly spread inland again Wed evening, eventually up to 15 miles inland by 12Z Thu with similar bases/tops. Confidence in a period of SCT low clouds at KSAN today per the TAF is moderate-to- high. Mountains/Deserts...Mostly clear skies with unrestricted VIS will continue through Thu morning. Areas of FU will locally reduce VIS to 3-5 miles in the San Bernardino county mtns and adjacent high deserts from the Vista fire. Local west sfc winds with gusts 25-30 knots will occur again 22Z Wed-12Z Thu through mountain passes/desert slopes, along with weak-locally MOD UDDFS. && .MARINE... No hazardous marine conditions are expected through Sunday. && .FIRE WEATHER... The air mass is very dry still above the marine inverion but southerly flow is developing behind the upper ridge which will bring the tropical moisture in monsoon fashion Friday 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/FIRE WEATHER...Tardy AVIATION/MARINE...Small