Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
152 FXUS66 KSGX 211602 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 902 AM PDT Tue May 21 2024 .SYNOPSIS... A slight warming trend through Wednesday, followed by a cooling trend Thursday through Saturday with a deeper marine layer and more low cloud coverage. There will also be stronger and gusty southwest to west winds for the mountains and deserts. High pressure then brings a warming trend for Sunday into the middle of next week with the marine layer becoming gradually shallower. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This mornings MSAS MSLP data showed surface high pressure sitting over the Eastern Pacific, while some offshore flow was noted at various higher elevation observation sites in SoCal. This is likely the culprit for the earlier and rather random clearing pattern seen this morning. The offshore flow and some slight height increases later today will result in a shallower marine layer tonight into tomorrow, as well as slightly warmer temperatures today and Wednesday. Low clouds will still be extensive enough to cover much of the coasts and valleys Tuesday morning, with slightly less coverage Wednesday morning. For Thursday into the weekend, troughing at 500mb will expand over the Southwestern US. This will enhance the onshore flow again, with a coastal eddy also forming Thursday and Friday. Ultimately this means more marine layer coverage across much of the coasts and inland valleys, lasting later into the mornings and afternoons from Thursday through the weekend. Clearing at the coast may be very slow and ultimately limited in spots Friday and Saturday. Temperatures will also steadily cool again during this time, ultimately topping out nearly 5 to 10 degrees cooler than seasonal normals at the coast and 10 to 15 degrees cooler than normal in the valleys and mountains. Sunday and Monday will see troughing weaken and eventually give way to ridging at 500mb, leading to a steady warming trend early next week. The marine layer will also become more shallow during this time, and steadily begin to clear out earlier each day. There will still be some degree of morning cloud cover across the coasts and valleys each day. Temperatures will rebound to near seasonal average by next Tuesday in the coasts and valleys, while the deserts begin to see triple digit highs reappear by Monday or Tuesday of next week. && .AVIATION... 211530Z...Coast/Valleys/Foothills...Low clouds with varying bases of 1800-3500 feet MSL and tops to 4200 feet will continue this morning. Foothill terrain locally obscured in clouds/fog. Clearing will occur in most areas by 19Z, but with partial or intermittent clearing at some coastal areas. Low clouds will push inland after 02Z and fill the coastal basin overnight into Wednesday. Bases would be 1500-2000 feet MSL with more vis restrictions across the Inland Empire and some coastal mountain foothill areas. Mountains/Deserts...Clear skies with unrestricted VIS will continue today and tonight. W-NW winds increasing again later this afternoon and evening with peak wind gusts of 20-30 kts expected. && .MARINE... No hazardous marine 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...None. PZ...None. && $$ PUBLIC...Adams AVIATION/MARINE...Adams