Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
286 FXUS66 KSGX 120937 CCA AFDSGX Area Forecast Discussion...corrected National Weather Service San Diego CA 237 AM PDT Sun Oct 12 2025 .SYNOPSIS... Cooler with night and morning low clouds in the coastal areas and valleys through Monday morning. A low pressure system moving southward along the West Coast will bring stronger onshore winds Monday into Wednesday morning, along with a chance of showers from the coast to the mountains Monday night into Tuesday night. Gradual warming and drying with periods of weak offshore flow Wednesday through Friday. For next weekend the warming continues inland while marine layer clouds and fog return to the coastal areas. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This morning...The marine layer has deepened by at least 1000 ft since yesterday morning under broad upper level cyclonic flow. The inversion is weak and the atmosphere is very dry above the marine layer. Low clouds are increasing in coverage and a weak coastal eddy is helping to spread the low clouds into the San Diego County valleys. High-resolution models indicate that low clouds will cover much of the San Diego and Orange County coastal areas, and could even spread into the southern IE before sunrise. Cool and breezy conditions will continue into Monday, with marine layer low clouds returning for tonight into Monday morning. Temperatures today will be near or a few degrees below normal. Monday will be cooler with inland temperatures as much as 12 degrees below normal. A reinforcing shortwave from western Canada will move southward along the coast on the upstream side of the mean trough over the western US. A closed upper low will form over the WA/OR coast by tonight and reach central CA by Tuesday morning before turning inland and moving eastward into the Rockies by Wed afternoon. This system will bring colder air, strong and gusty westerly winds and chances for showers and high-elevation snow. Tuesday will likely be the coldest day with daytime temperatures as much as 10-20 degrees below normal in the inland valleys, mountains and deserts. Temps in the inland valleys will be in the mid 60s and in the mid 70s to about 81 in the low deserts. Southwest to west winds will begin to strengthen on Monday and peak Mon night/Tue morning, with wind gusts of up to 55 mph in the wind-prone locations of the mtns and deserts. Showers could move into the areas bordering Los Angeles County as early as Monday evening, spreading south and east through Tuesday before ending Tuesday night as the system moves east into the Rockies. Rainfall totals will favor the slopes of the San Bernardino mtns where some locations could get 1+ inches of rainfall. Farther south and east, amounts will decrease and estimates for Southern San Diego County are for one tenth or less. The high deserts could receive about one third inch and the low deserts a few hundredths of an inch. Snow levels will be mostly between 7500 and 8000 ft, and minor snow accumulations are likely above resort elevations. Gradual warming is expected for Thu-Fri under weak upper level troughing as the system continues to move eastward into the Great Plains. A weak sfc high in the Great Basin will produce weak offshore gradients, enough to limit the return of any marine layer clouds. In spite of the warming, inland temperatures will still be a few degrees below normal. For next weekend...Model solutions diverge significantly but a plurality of ensemble members across model platforms show weak high pressure ridging over SoCal. The gradual warming trend will likely continue, although daytime temps will still be a few degrees below normal. A shallow marine layer could return with low clouds and fog in the coastal areas during the nights and mornings. && .AVIATION... 120900Z....Coasts/Valleys...Large patch of low clouds based around 1500 ft MSL present in San Diego Co up to 20 miles inland this morning. Low clouds expected to develop in Orange County towards 11Z, most likely in northern OC, with a 75% chance for CIGs at KSNA by 13Z. Weak offshore flow later this morning will clear clouds for the most part 15-16Z. Low clouds 1500-2000 ft MSL will form along coastal areas after 13/07Z, initially patchy then becoming more widespread towards 09Z. CIGs will rise overnight through Mon morning, spreading into most of the coastal basin by late Mon morning. Mountains/Deserts...VFR conditions expected through the TAF period. && .MARINE... No hazardous marine conditions are expected through Monday, though winds will be breezier than average out of the southwest Monday afternoon. A weather system approaches the area Tuesday, with increasing winds out of the south to southwest. Gusts 20-25 knots and choppy seas possible throughout the coastal waters Tuesday morning through the evening. && .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...CSP