Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
687 FXUS66 KSGX 172025 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 125 PM PDT Sun Aug 17 2025 .SYNOPSIS... Low pressure along the West Coast will bring cool weather and extensive coastal clouds early this week. High pressure will build this week, bringing a warming trend and less marine layer cloud cover. Thursday through Saturday will be the hottest days. Monsoon moisture and the chance of showers and thunderstorms will increase, mainly over the mountains and deserts Thursday through at least Sunday, with the highest chance Friday and Saturday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Skies cleared quite fully even from the beaches today, and with less smoke and haze, you can see the mountains much better. The coastal eddy will continue to weaken as low pressure over the West Coast gives way to high pressure building and expanding over the Southwest. The higher pressure will push down on the marine layer and warm SoCal`s air mass over the next few days. As the ridge axis moves northward, the door will begin to open for monsoonal moisture to flow in from the southeast. This will be a gradual process, increasing a little each day Monday through Friday. Each day will be a little warmer, the marine layer cloud cover a little more confined to the coast. While temperatures today are very much on the cooler than average side, by Wednesday they rise to around average, then above average Thursday through Saturday, when max temps will be 2 to 10 degrees above average. Look for temps in the Inland Empire 97-105, high desert 98-107, low desert 109-115, western valleys in the 90s, 80s near the coast and and mid-upper 70s at the beaches. The monsoon flow could bring gulf surges into the low desert each morning, which would dampen the max temp potential there on those hottest days. The monsoonal moisture and instability eventually become sufficient to produce some showers and thunderstorms Thursday and beyond. Look for the first isolated thunderstorms in the mountains Thursday afternoon. Then on Friday and Saturday the chances increase and expand in space to all mountains and deserts, and also expand in time into early evenings. We`ve been watching guidance play this same tune for several days now, so our confidence is relatively high for this scenario to play out through Saturday. Six days is pretty good for a narrow range of outcomes, so we`ll take it. For next Sunday, ensembles widen the range of outcomes, but most solutions indicate a tepid cooling trend to begin and a gentle nudge aside of monsoonal moisture for decreasing chances of thunderstorms. && .AVIATION... 172000Z...Coast/Valleys...Full coastal clearing occurred with low clouds lingering 5-10 miles offshore. Low clouds fill in and push back ashore after 00-02z Monday, initially across San Diego County, eventually filling into Orange County after 09z. Bases will be similar to this morning, albeit 100-200ft lower, around 1000-1500ft MSL. VIS down to 2-5SM for coastal terrain. Clouds will struggle to make it more than 10-15 miles inland through Monday morning, with only a 25% chance of a CIG at KONT. Similar to this morning, low clouds will retreat to the coast by 17z, with likely full clearing by 19-20z. Mountains/Deserts...Mostly clear with VFR conditions prevailing through Monday. && .MARINE... No hazardous marine conditions are expected through Thursday. && .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...MM AVIATION/MARINE...Zuber