Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
014 FXUS66 KSGX 230403 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 903 PM PDT Wed May 22 2024 .SYNOPSIS... After a slightly warmer day, a cooling trend with a deeper marine layer sets in for Thursday-Saturday. Temperatures will be significantly cooler than seasonal normals by Saturday, anywhere on the order of 5-15 degrees cooler. There will also be chances for patchy drizzle on Saturday. High pressure then builds in starting Sunday, leading to a steady warming trend and a shallower marine layer through the middle of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Evening Update... No major forecast changes this evening as low clouds continue to progress inland, slowly filling in the coastal basin. Low temperatures will be within a few degrees of average tonight with temperatures dipping up to 10 degrees below average for inland valleys by Thursday afternoon. Friday still looks to be the windiest day overall for mountains and deserts as a trough moves through. There is a low to moderate chance in winds reaching 45 MPH, best chance across mountain passes and desert crests. This trough will also bring cold temperatures Friday and Saturday. .Previous Discussion (127 PM Wednesday)... This afternoon and evening will see the expansion of a 500mb trough over the Southwest US, as well as the development of a coastal eddy overnight. The trough expansion and subsequent strengthening of the onshore pressure gradients will lead to an uptick in the onshore flow, with gusty west winds occurring primarily over the mountains and deserts each afternoon and evening through Saturday. Peak wind gusts will be in the 40 to 50 mph range, with locally higher gusts over ridgelines, below passes, and through canyons, strongest winds currently look to occur Friday afternoon/evening. Meanwhile, the coastal eddy will act to re-deepen the marine layer more and more through Saturday, so low clouds will continue to cover much of the inland valleys and coastal areas each morning, and may last longer into the afternoons over inland areas. By Saturday, the marine layer may be deep enough to support patchy drizzle in spots. Highs Friday and Saturday will also be significantly cooler than seasonal average, generally on the orders of 5-10 degrees cooler than normal at the coasts and in the deserts, and 10-15 degrees cooler across the inland valleys and mountains. Sunday will finally see the trough move eastward as high pressure sets in. This leads to a steady warming trend through the middle of next week, as well as a shallower marine layer each day. The marine layer will likely be at its shallowest by midweek, though some degree of low clouds will occur over the coasts and some of the inland valleys every day. The lower deserts will see temperatures rebound to the middle 90s on Sunday, with triple digit readings occurring in many lower desert locations by Memorial Day. Outside of the deserts, temperatures early next week will generally be in the upper 60s to lower 70s at the coast, middle 70s to middle 80s across inland valleys with the warmest temperatures in the Inland Empire, and the upper 60s to near 80 in the mountains, elevation dependent. && .AVIATION... 230400Z...Coast/Valleys/Foothills...Low clouds spreading inland, with bases 1500-2500 ft MSL and tops to 3000 ft MSL. Low clouds expected to spread inland to the coastal slopes by 13Z Thu morning, obscuring higher terrain with areas of reduced VIS 1-3SM where clouds and terrain intersect. Mostly clear in the afternoon except for some SCT-BKN clouds with bases around 2500 ft MSL and tops to 3500 ft MSL near the beaches. Low clouds flowing inland again after 01Z Thu afternoon. Mountains/Deserts...Clear skies with unrestricted VIS through Thursday night. W-NW wind gusts of 20-35 kt over/east of mtns after 00z Thu afternoon, with weak-mod up/downdrafts and LLWS over/east of the mtns. && .MARINE... Northwest winds gusting near 20 knots in the outer waters each afternoon and evening Friday through Sunday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...APR/BA AVIATION/MARINE...Small