Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
133 FXUS66 KSGX 190343 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 843 PM PDT Fri Jul 18 2025 .SYNOPSIS... Slight chances of showers and thunderstorms in the mountains Saturday afternoon. Dry conditions will return for Sunday through next week. Temperatures will remain mostly below average. Marine layer low clouds and fog will reach into portions of the valleys each night and morning. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... At 8:30 PM, low clouds were developing along the coast and beginning to move inland, with areas of high clouds across San Bernardino County. Shower and thunderstorm activity diminished around 5 PM, with dry conditions expected to prevail overnight. Showers and thunderstorms are expected to develop over the mountains Saturday afternoon. Rainfall rates are expected to be 0.25 inches per hour or less, with a 5 percent chance of higher rainfall rates occurring. Dry conditions return for Sunday. From previous discussion issued at 2 PM July 18... Leftover moisture and instability over the mountains will leave around a 15-20% chance of thunderstorms in the mountains Saturday afternoon. The marine layer will maintain its presence through the weekend, especially in San Diego County tonight, building across much of the coast by the weekend. By Sunday, a trough of low pressure will move into the Pacific Northwest. This will bring cooler and drier air to California, helping to push monsoonal moisture further east. Tranquil weather will return to the region Sunday through at least the middle of next week. Ensemble guidance shows the trough deepening into Northern California by the middle of the week. This pattern will create temperatures near to around 10 degrees below normal with dry conditions. The marine layer will become deeper during this time period, with night and morning low clouds moving in for the coast and adjacent valleys. && .AVIATION... 190300Z....Coast/Valleys...low clouds with bases around 1500 feet MSL will return into full coverage through the evening, mainly after 06Z. This will scatter out by 17Z, and then begin to regather and fill back in tomorrow evening beginning around 01-02Z Sun along the coast initially, then extend eastward to around 15 miles inland, and within portions of the Imperial Empire, with similar base heights. Mountains/Deserts...SCT-BKN clouds 10000-15000 feet, becmg ISO-SCT overnight. ISO TSRA (20% probability) tomorrow aftn over mtns, with a 10% chance in adjacent deserts/valleys, with CU/CB bases 8000- 10000 feet MSL, tops to 35000 feet. Erratic wind gusts, strong up/downdrafts, and VIS restrictions possible with any TSRA. Gradually clearing after 00Z Sun. && .MARINE... No hazardous marine weather expected through Wednesday. && .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...CO AVIATION/MARINE...Stewey