FXUS66 KSGX 070431 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 930 PM PDT Sun Apr 6 2025 .SYNOPSIS... Fair warm weather will prevail this week. Patchy low clouds and locally dense fog should return to the immediate coast by Monday morning and likely again Monday night and Tuesday morning. Inland highs will be 10 to locally 20 degrees above normal Wednesday through Friday. Cooler weather will return next weekend. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Update... SKies were mostly clear, though Low clouds and fog are over the parts of the coastal waters near San Clemente and Catalina Islands. There is around a 70 percent chance at least some low clouds/fog will reach the coast by sunrise Monday, and the fog could be locally dense due to the initial shallow marine layer. Farther northwest, Oxnard currently has cloud ceilings of 300 feet which highlights the shallow marine layer, and often the ceilings and visibilities go down overnight in this pattern. Otherwise, the increasing heat inland is still on track with Palm Springs having 2-3 days at/above 100 F Wed-Fri, but following by a cooling trend over the weekend, though confidence is low on how rapid that trend will be. From previous discussion... For Monday and Tuesday...Inland temperatures contiWarm and fairnue the upward trend while the upper level ridge weakens in response a low pressure trough moving inland to the north. The resulting onshore flow and the return of the marine layer will moderate temperatures in the coastal areas and western portions of the inland valleys. Daytime temperatures will range from the upper 60s at the beaches to the low 80s in the inland valleys. The upper deserts will be in the upper 70s to lower 80s and the lower deserts will be in the low to mid 90s. For Wednesday through Friday...A large-amplitude ridge of high pressure builds over the western states. This will bring significantly warmer conditions and a reduction in the marine layer presence, limiting the nocturnal low clouds and fog to the immediate coastal areas. Thursday will likely be the warmest day, with daytime high temperatures in the low 90s for portions of the inland valleys and upper deserts. High temperatures in the lower deserts will be near 100 degrees at some locations. The national Blend of Models shows a 55-90 percent chance of 100 degrees or more on Thursday in the lower deserts. It also shows a 70-90 percent chance of 90 degrees or higher in the IE and upper deserts. Except for the lower deserts where temperatures could be a little higher, Friday will not be quite as warm as the upper level ridge begins to shift eastward and heights/thicknesses begin to lower as a trough of low pressure approaches from the northwest. The trough will take control of SoCal weather for next weekend, bringing stronger onshore flow with more clouds and lower temperatures. By next Sunday, temperatures west of the mountains will be back down to the 60s and 70s. In the high deserts, temperatures will be back down to the 70s and in the lower deserts the upper 80s to near 90. There is still significant uncertainty in the forecast details for the weekend due to the spread in the ensemble member solutions. && .AVIATION... 070330Z...VFR and clear skies continue this evening though chances for low clouds and fog look to increase after 09z Monday. Current thinking is that these clouds, if they do arrive, would be based near 300-500ft MSL and bring VIS down to 1-3 SM, locally less than 1 SM along the higher coastal terrain. CIG/VIS restriction chances peak between 12-16z. Any low clouds/BR/FG that do develop will scatter out by 16-17z Monday, with full clearing by 18z. There is a40-60% chance of seeing CIG/VIS reductions described above at KSAN and KSNA between 12z-16z, with a 30-40% chance for KCRQ. && .MARINE... Patchy fog could bring visibilities near 1SM tonight, clearing Monday morning. No hazardous marine conditions are expected through Friday. && .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...Maxwell (Update)/PG (Previous Discussion) AVIATION/MARINE...Munyan