Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
492 FXUS66 KSGX 170423 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 923 PM PDT Tue Jul 16 2024 .SYNOPSIS... Gradual increase in temperatures each day for most areas through Saturday. Above average temperatures are expected for all areas by the weekend, with moderate to major heat risk for the valleys and major to extreme heat risk for the deserts. Major to extreme heat risk could continue for the deserts into early next week. There are slight chance of showers and thunderstorms each afternoon in the mountains into early next week. Coastal low clouds and fog will continue to reach into portions of the western valleys each night and morning. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... No thunderstorm activity was detected in the forecast area this afternoon. Satellite imagery from earlier this afternoon was showing areas of cumulus clouds over the mountains, but they weren`t able to develop enough vertically for convection to occur. The 00Z sounding showed an inversion at the mid-levels which is likely what put the cap on the thunderstorm activity this afternoon. There are slight chances of thunderstorms in the forecast for tomorrow afternoon, mainly in the mountains. Southerly to southeasterly flow aloft will keep the door open for monsoonal moisture into early next week. Current forecast maintains slight chances of showers and thunderstorms in the mountains each afternoon into early next week. One factor that could hinder thunderstorm activity this weekend is the location of the high pressure system. The high is forecast to move west away from the Four Corners and more over the Great Basin/California. The high may provide too much subsidence or stable air over the area for thunderstorms to develop. From previous discussion issued at 2 PM Tue July 16... A high pressure ridge over the West will strengthen a little each day Wednesday into Saturday. That will bring a modest warming trend taking near normal high temperatures Wednesday to 5-10 degrees above normal over the weekend. That will mean going above 104 in parts of the Inland Empire and above 114 in parts of the lower desert. One caveat to watch for is how much if any low level moisture seeps into the low desert each morning, moisture that would literally dampen any temperature rise. The latest GEFS ensemble really goes crazy with this idea, grossly under forecasting desert temps. But it really doesn`t matter: the heat risk will be high whether the temp gets to a dry, scorching 118 or a humid, sweltering 108. With the high over the West strengthening, the marine layer will get suppressed slightly and low clouds should not make it into inland valleys anymore for a while. But the warm air mass and strength of the high will keep the marine inversion nice and strong. No, the low clouds aren`t going anywhere, just backing off a step. The strong high pressure over the Southwest is also not going anywhere, so it looks like temps will remain well above normal next week. && .AVIATION... 1704000Z...Coast/Valleys...Satellite shows low clouds holding off the San Diego coast which will slowly build inland, with CIGs developing at most coastal sites 17/04z-17/10z. Bases will be slightly higher compared to previous nights between 1100-1500ft MSL with tops to 1400-1700 ft MSL. Visibility reductions to around 3SM possible in the valleys and higher coastal terrain overnight. CIGs scatter out for most coastal sites by 17/17z with the redevelopment of low clouds not expected for any sites before 18/05z. Mountains/Deserts...Low TSRA/SHRA chances in the vicinity of the mountains late Wednesday morning through the afternoon with SCT- BKN120. While no impacts to TAF sites are expected, gusty winds, lightning, and localized vis reductions will be a threat in the vicinity of any storm. Strong up/downdrafts will be possible near the mountains. && .MARINE... No hazardous marine conditions are expected through Monday. && .BEACHES... Long period 3ft SSW swell (200-210 degrees) will bring elevated surf of 4-6 feet with sets up to 7 feet for south and southwest facing beaches in both Orange and San Diego counties. A Beach Hazard Statement is in effect through Thursday evening. The period will decrease on Thursday with swell height falling to 2 ft. There is a high risk of dangerous rip currents, which will continue into Friday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement through Thursday evening for Orange County Coastal Areas-San Diego County Coastal Areas. PZ...None. && $$ PUBLIC...CO/MM AVIATION/MARINE/BEACHES...Zuber