Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
393 FXUS66 KSGX 251638 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 938 AM PDT Sat May 25 2024 .SYNOPSIS... Slightly cooler today in some areas, with gusty southwest to west winds in the mountains and deserts. Low clouds covered all areas inland across the valleys and onto the lower coastal slopes of the mountains this morning and only partial clearing is expected by 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... This morning, the sounding and aircraft reports show the marine layer at about 4000 ft deep with low clouds covering the region west of the mtns and reaching to the top of the Cajon Pass. Breaks are appearing in the clouds at this hour but widespread clearing has not yet begun. Cooling aloft has weakened the marine layer inversion which usually allows for mixing of the boundary layer and more clearing of the low clouds but the near-saturated layer below the inversion is about 2000 ft thick which will work against more efficient clearing of the clouds. This cooling represents a significant change from what has occurred in the last several days. The High-res ensemble models show some clearing across the Inland Empire and northern parts of Orange County this afternoon, with much less clearing in San Diego County. Inland away from the marine layer influence, gusty westerly winds will continue across portions of the mountains and deserts through this evening, with a peak this morning and again this afternoon. Gusts will mostly be around 30-45 mph with isolated gusts to around 55 mph through the San Gorgonio Pass. Temperatures will be lower than yesterday in some areas at but generally 8-18 degrees below normal inland and around 4-7 degrees below normal near the coast. 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... 251535Z...Coast/Valleys/Coastal Slopes...BKN-OVC with bases 2000- 3000 FT MSL are occurring this morning. Iso DZ/-SHRA continuing through 18z with locally reduced vis in SHRA. Scatter out across Inland Empire/inland Orange County 18z-22z with limited clearing across San Diego and the coast this afternoon. Widespread BKN-OVC again tonight-Sun morning. Bases will be similar, if not slightly lower than today, generally in the 1500-2500 FT MSL range. Mountains/Deserts...Mostly clear through tonight. W-SW gusts of 20- 35 kt 18z Sat-10z Sun. Local VIS 3-5 SM will occur in local BLDU. && .MARINE... West to northwest winds around 20 knots will occur in the outer coastal waters each afternoon and evening through Monday. && .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...Adams