Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
075 FXUS66 KSGX 102052 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 152 PM PDT Wed Jul 10 2024 .SYNOPSIS... The upper ridge is over southeast California and 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... The strong inversion with the upper ridge over southeast California has held the marine clouds 2-3 miles inland...slightly further east than yesterday. The lower marine layer will result in coastal fog again late tonight. 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. Satellite depicts the monsoon wind pattern setting up with altocumulus now moving northward across Socal. 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 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... 102040Z...Coast/Valleys...BKN-OVC clouds with bases 600-1000 ft MSL and tops to 1200 ft MSL over the coastal waters extending locally inland. Low clouds will slowly spread inland again Wed evening, eventually up to 15 miles inland by 12Z Thu with similar bases/tops and higher terrain locally obscured. Local VIS 1-3 miles will occur over higher coastal terrain through 16Z Thu. Confidence in the arrival time of BKN-OVC low clouds at KSAN Wed evening per the TAF is moderate-to-high. Mountains/Deserts...Mostly clear skies with unrestricted VIS will continue through Thu morning. Areas of HZ 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. && && .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...Tardy AVIATION/MARINE...Small