Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
478 FXUS66 KSGX 062038 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 138 PM PDT Sat Sep 6 2025 .SYNOPSIS... Mostly clear skies with near average temperatures will occur across the region this weekend. Monsoonal moisture continues to lower, so slight chances of weak showers and thunderstorms may occur over the mountains this weekend as well. Drier weather is expected across all areas next week. A noticeable cooling trend is expected by the middle of the week with highs from 5 to 15 degrees below average with breezier conditions across the deserts and adjacent mountains. The marine layer will also be deeper next week, contributing to clouds and fog west of the mountains each night and morning. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Cumulus clouds have built up over the mountains, but remain on the flatter side this afternoon. Minor instability and lower monsoonal moisture can be expected this weekend, so storm chances will be limited to around 15 to 20 percent, even though a slight increase in PWAT is noted. Whatever falls will be light across the Riverside/San Diego Co mts into Sunday. A trough setting up offshore should also help keep shower activity weaker as well on Sunday if any showers do occur. The trough off the coast will move closer to the region by Monday, deepening through Wednesday. This will allow for greater cooling and onshore flow to overspread the area. Near average temperatures this weekend will lower to around 5 to 15 degrees below normal. There is moderate to high confidence in high temperatures staying below 80 degrees in portions of the Inland Empire, high desert, and the San Diego Co valleys by Wednesday. Increasing west winds will also occur across the mountain desert slopes into the deserts by the middle of the week. NBM mean wind speeds are generally 25-35 MPH, though higher percentile speeds are closer to 30-45 MPH. This pattern will favor windy conditions to ramp up across the San Gorgonio Pass as well, where winds may near 55-60 MPH each day. The marine layer will also deepen during this time with night and morning low clouds/fog to push inland for many areas west of the mountains. Ensemble models show a weakening of the trough by the end of next week, but no strong signals on any large features impacting the area by next weekend. This will help temperatures rise closer to normal by the end of the week. Drier and calmer weather looks to continue for the foreseeable future. && .AVIATION... 061930Z...Coast...Low clouds with bases around 1000 feet MSL are hugging the coastline, and it may go periodically BKN-OVC throughout the afternoon hours. Low clouds will redevelop over coastal waters later this evening and push into coastal land areas after 06Z Sunday. Expecting slightly lower bases as the previous night, and less inland extent. Initial clearing of the marine layer inland will occur around 13-14Z Sunday for the foothills, and then erode from east to west to the coast by around 16-17Z Sunday. Valleys/Mountains/Deserts...Low chances this afternoon through early evening (10-20% probability) for SHRA over mountains and 5-10% chance of isolated TSRA through 01Z Sat (mostly mountains of San Diego and southern Riverside counties). CB bases around 10K ft and any TSRA tops to 35K ft. Any TSRA will bring gusty, erratic winds, blowing dust with low visibility, lightning, and lower bases 6000- 9000 feet MSL. There will still be slight chance of occurrence over the mountains tomorrow during the afternoon, although even lesser of a chance, and likely only SHRA. && .MARINE... No hazardous marine conditions are 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...Stewey