Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
411 FXUS66 KSGX 020912 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 212 AM PDT Sat Aug 2 2025 .SYNOPSIS... Temperatures near average and marine layer low clouds each night and morning along the coast and in the western valleys through Tuesday. High pressure over the Desert Southwest will strengthen the latter half of next week, bringing a warming trend with temperatures 5 to 10 degrees above average away from the coast. There is the potential for monsoon moisture to return late in the week but precipitation chances remain below 10 percent. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Marine layer low clouds have filled in along the coast and spread into the western valleys again this morning. Elsewhere skies remain clear. Low clouds will clear by late morning. An upper level high centered near southern Arizona will shift westward towards California today, bringing a couple more degrees of warming for inland areas while coastal areas remain moderated by the marine layer. In general highs will be near normal for most areas, and around 3-5 degrees above normal in the deserts. This high stays in place Sunday, then slowly weakens and shifts back eastwards Monday and Tuesday as an upper level trough moves by to the north. Overall only minor temperature fluctuations are expected for the early part of the week with night and morning low clouds continuing for the coastal areas and far western valleys. Ensembles are in very good agreement with the upper level high strengthening over AZ/NM during the second half the week. This will bring more warming inland, with the peak of the heat likely occurring Thursday with minor cooling Friday. About 30% of the ensemble space keeps warmer weather into Saturday while the remaining members are cooler with the upper high weakening. For Thursday, highs will be around 5-10 degrees above normal inland and around 3-5 degrees above normal near the coast. There is a 70-90% chance of high temperatures of 100 or more in the interior portions of the Inland Empire and a 70-100% chance for lower elevations of the upper desert. There is a 60-90% chance of high temperatures of 115 or more across the low deserts, but a less than 10% chance of temperatures of 120 or more. Widespread high HeatRisk is forecast across the lower deserts and moderate HeatRisk for the mountains and valleys on Thursday, with decreasing coverage on Friday. All global ensembles have a modest increase in precipitable water beginning Tuesday or Wednesday with a continued slow increase through the end of the week with ensemble means near 1-1.25". With the east-west ridge axis almost directly overhead we will still lack the instability for showers/thunderstorms, so forecast remains dry. Low level moisture intrusions from the Gulf of California are still a possibility for late in the week, which would result in slightly lower air temperatures during the day but more humidity/higher heat indices. && .AVIATION... 020830Z....Coasts/Western Valleys...Low clouds based 700-1200ft MSL have successfully moved inland with very limited filtering into the Inland Empire. Bases will lower closer to 700-900ft MSL through 13z. VIS down to 1-5SM primarily for coastal terrain and valleys. Clouds clear to the beaches by 17z, redeveloping again tonight and moving inland after 05z Sunday. Bases tonight will be similar to this morning, around 700-900ft MSL. .Inland Valleys/Mountains/Deserts...Mostly clear with VFR conditions through Sunday morning. && .MARINE... No hazardous marine conditions are expected through Thursday. && .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...SS AVIATION/MARINE...Zuber