Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
195 FXUS66 KSGX 260401 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 901 PM PDT Sat May 25 2024 .SYNOPSIS... Slightly cooler today in some areas, with gusty southwest to west winds in the mountains and deserts. Only partial clearing of the low clouds this afternoon. High pressure to the south will bring some warming for Sunday through Thursday, more noticeable inland. The marine layer will become shallower with night and morning coastal low clouds only extending into western portions of the valleys by the middle of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Evening Update... Gusty west and northwest winds continue this evening across the Coachella Valley and adjacent San Gorgonio Pass with winds near 25-35 MPH at times across the valley floor. Winds will remain gusty this evening, weakening by sunrise. Weaker winds can be expected for these areas by Sunday into much of next week. Clearing today was a bit greater than expected, especially for inland valleys. Clouds currently filling into the coastal basin will scatter out even better by Sunday, with HREF clearing many areas in the IE and Orange County by the afternoon hours. Though the marine layer will become shallower, areas of party to mostly skies may hang on into the afternoon across coastal San Diego county. Better chances for clearing for all areas will occur by the Memorial Day holiday with warmer weather. .Previous Discussion (121 PM PDT Saturday)... Troughing continues to dominate the pattern over the western U.S., bringing unseasonably low temperatures and breezy conditions today. There is good consensus among ensemble members across model platforms through Wednesday then solutions tend to diverge more. Indications are for the trough to move east on Sunday, allowing for height rises with near-zonal flow aloft. This will produce somewhat higher temperatures and reduced coverage of marine layer low clouds. Daytime highs will be 5-10 degrees higher on Sunday away from the coast, though still several degrees below normal. There will likely also be better clearing of the low clouds inland, although clearing at the coast could be restricted if the height rises were to strengthen the marine layer inversion. Through Wednesday, the upper level high centered over central Mexico will gradually shift westward and a north-south ridge axis will amplify downstream of a low pressure system intensifying in the Gulf of Alaska. There will be competition between the trough associated with the low and the building ridge. For SoCal this will likely result in modest warming across the region on Monday with little variability through Wednesday. Daytime high temps will generally be close to seasonal normals during this period. The effects to temps will be much more significant over the Great Basin and the Rockies. The marine layer will be shallower, with low clouds and fog limited to the coastal areas and western valleys each night and morning, and there will be a better chance of clearing each afternoon including on the Memorial Day holiday. After Wednesday, ensemble solutions begin to diverge significantly with respect to the progression and strength of the low pressure system in the Gulf of Alaska as it moves across the Pac Northwest and the subsequent ridging that follows behind it. About 50% of ensemble members favor more of a ridge/warmer weather over the west coast, 25% a trough with cooler weather, and 25% somewhere in between. The cluster analysis suggests that members favoring either solution generally break down by model platform. Members from the same model platform tend to favor similar solutions. This continues into the weekend. The temperature forecast reflects the NBM solution which maintains near seasonal temps through the end of the week. && .AVIATION... 260400Z...Coast/Valleys...Areas of BKN-OVC clouds with bases 1500- 3000 ft MSL and tops 2500-5500 ft MSL will occur through 17Z Sun with mostly unrestricted VIS below the clouds. Higher terrain will be locally obscured through 16Z Sun. Earlier clearing will occur Sun with valleys clearing 15Z-17Z with patchy BKN clouds with bases 2000-2500 ft MSL continuing near the coast through Sun afternoon. Low clouds will be more patchy with lower bases Sun evening, mostly at/below 1500 ft MSL. Mountains/Deserts...Local terrain obscurations in clouds on coastal slopes below 5500 ft MSL will continue through 16Z Sun. Otherwise, mostly clear skies will continue through Sun evening. Areas of W-SW surface gusts of 25-40 kt will continue through 13Z Sun from the mountain crests east through the desert slopes and into the deserts, including near San Gorgonio Pass, with MOD UDDFS over/east of the mountains. Local VIS 3-5 SM will occur in BLDU. Lighter winds will occur Sun afternoon/evening with gusts mostly remaining under 30 kt. && .MARINE... West to northwest winds around 20 knots will occur in the outer coastal waters (30-60 NM from the coast) each afternoon and evening 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...APR/PG AVIATION/MARINE...Maxwell