Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
350 FXUS66 KSGX 211644 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 944 AM PDT Sat Sep 21 2024 .SYNOPSIS... A warming trend is expected through Monday. The marine layer will become shallower into early next week, becoming more confined to the coast and portions of the western valleys. For Tuesday through the end of the week, minor daily fluctuations in high temperatures are expected. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This morning...The marine layer is about 3500 ft deep and low clouds cover most of the region west of the mountains, except for San Diego County south of Encinitas. Some low clouds are currently pushing ashore south of Del Mar but the clearing process has already begun inland. Clearing to the coast is likely by 11 am. Temperatures are generally a few degrees lower than at this time at the lower elevations west of the mtns while in the mtns and deserts temps are mostly a few degrees higher. Through Tuesday... The low pressure system that brought us the active weather yesterday has moved east and we are under northerly flow aloft with increasing heights. Broad troughing over the western U.S. will keep us under weak cyclonic flow aloft with rising heights. As a result, SoCal will experience a warming trend. Monday looks like it will be the warmest day, with daytime temperatures near or up to 9 degrees above seasonal averages. As is often the case the highest temperatures west of the mtns will be in the Inland Empire where temps will be in the lower to upper 90s. Temps in the lower deserts will return to the low triple-digits. The marine layer will become shallower and the low clouds/fog will be mostly confined to the coastal areas, inland Orange County and the western portions of the San Diego County valleys. By Tuesday, there will be a weak upper level low to the west with an upper level high to its north, forming a weak Rex Block. Wednesday through Saturday... A low/trough moving out of the Gulf of Alaska will seek to disrupt the block. As the trough approaches the Pac Northwest, the high will be displaced eastward and the closed low will be drawn northward. As this process unfolds, the numerical models struggle to reach a consensus solution. The resulting differences in model solutions will inject significant uncertainty into the forecast. At this time, most ensemble members across model platforms suggest that temperatures will be marginally lower for Wednesday with only slight day-to-day variations through next Saturday. Likewise, the marine layer will recover slightly with only small day-to-day variations, although the low clouds will be unlikely to extend farther inland than the western portions of the valleys during the nights and mornings. && .AVIATION... 211545Z...Coasts/Valleys...Low marine stratus (based around 1500- 2000ft MSL, topped to 1800-2300ft MSL) with vis 1-3SM in BR for higher coastal terrain and valleys. Scattering out will occur for most locations by 18-19z, though some stratus may linger near the beaches through the afternoon. Confidence in clearing time at KSAN is low-moderate. Low stratus builds in again for coastal sites around 03-06z this evening with bases near 800-1200ft MSL and tops to near 3000 feet. Mountains/Deserts...Mostly clear skies with unrestricted VIS expected through Saturday evening. && .MARINE...No hazardous marine conditions are expected through Wednesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...PG AVIATION/MARINE...Small