Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
020 FXUS66 KSGX 182029 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 129 PM PDT Fri Jul 18 2025 .SYNOPSIS... Showers and thunderstorms will continue across the mountains and deserts through this evening as pesky marine layer clouds hover over parts of the coast. Monsoonal activity will decrease on Saturday with a minor chance of storms being focused in the mountainous regions. By Sunday into the middle of next week, a troughing pattern will take hold over the region, leading to dry weather with temperatures near to below average with marine layer clouds closer to the coast each morning. This pattern may linger into later next week as well. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Radar imagery shows isolated thunderstorms over the San Bernardino mts early this afternoon as an area of low pressure over northern Baja pulls in monsoonal moisture. Storms located near Big Bear and Lake Arrowhead have produced rain rates over one inch per hour. Upper level winds remains stronger where adequate shear is present to aide in pulsating storms. Weaker shear is noted in the lower levels, where storm motion is fairly stagnant. This will lead to certain areas seeing localized flooding concerns. Storms may produce cloud to ground lightning, small hail and gusty winds. Hi- res models continue to show storm activity lasting until around 8PM this evening. The low will weaken on Saturday, but some leftover moisture and instability over the mountains will leave around a 15-20% chance of thunderstorms. 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... 182030Z....Coast...SCT, locally BKN, low clouds with bases around 1500 feet MSL will return in full after 04Z. Scatter out Saturday by 17Z. Valleys/Mountains/Deserts...SCT-BKN clouds 10000-15000 feet. ISO-SCT TSRA over the mountains, high desert and 20% chance in adjacent valleys through 02Z, with CU/CB bases 7000-9000 feet MSL, tops to 40000 feet. Erratic wind gusts, strong up/downdrafts, and VIS restrictions possible with any TSRA. Gradually clearing after 03Z. CU/CB based at 9000 feet MSL developing into ISO TSRA over mountains 19-00Z Saturday. && .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...APR AVIATION/MARINE...MM