Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
411 FXUS66 KSGX 252021 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 121 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... This afternoon, low clouds still cover most of the region west of the mtns but there are now spaces between the elements of stratocumulus through which sunshine is reaching the ground. We expect to see more breaks in the clouds for a few more hours before the coverage begins to increase again later this afternoon. In some locations, temps are a little higher than at this time yesterday and in some locations they are a little lower. Sfc pressure gradients remain onshore with 4.2 mb SAN-DAG and 6.2 mb SAN-IPL. Gusty westerly winds continue, with the wind-prone locations reporting gusts of 35-45 mph locally up to 62 mph at Whitewater. HiRes models indicate a weakening trend for the next several days. From previous discussion... 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... 251945Z...Coast/Valleys/Coastal Slopes...SCT-BKN with bases 2000- 4000 FT MSL are occurring over some coastal areas this afternoon, with some reverse clearing at the coast also evident on satellite. Additional clearing should occur across the Inland Empire/inland Orange County through 22z with limited clearing across southern San Diego County 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 continuing through 10z Sun, with MOD UDDFS over/east of the mountains. 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