Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
035 FXUS66 KSGX 161548 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 848 AM PDT Wed Jul 16 2025 .SYNOPSIS... A weak low pressure system from the south will bring an increase in mostly mid level monsoonal moisture on Thursday and Friday with a chance for mainly afternoon showers and thunderstorms, mainly for the mountains. Then drier for the weekend into the middle of next week. Thursday will be cooler for the deserts, but with an overall slight warming trend for most areas into next week. Night and morning coastal low clouds will continue to spread into portions of the western valleys late each night. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Low clouds and fog made it into western valleys this morning, but only barely into the Inland Empire. The cloud deck in our marine layer that`s 2000-2500 feet deep will take a little time to clear out late this morning, but should provide hazy but mostly sunny skies thereafter. We`re starting to sample the increasing mid- level moisture as the 12Z sounding showed 1.08 inches of precipitable water. This monsoon moisture will increase such that by Thursday morning we reach about 1.5 inches. This is coming from the south where a weak upper low resides off the central Baja Coast. By sunrise Thursday, there is a wave of unstable air accompanying the moisture, which hints at more widespread and elevated convective showers. But since the instability and depth of moisture appear insufficient for a credible chance of widespread showers, we expect some altocumulus and probably some virga anywhere with this Thursday morning wave. (Of course only visible for meteorological interest outside of the marine layer cloud deck). The legit chances of precipitation will need the surface heating and the higher terrain to get enough lift to trigger any thunderstorms. Right now the chances are slight and mainly in the mountains and the high desert east of I-15 during the afternoon and early evening. The moisture decreases a little for Friday so there will be less debris cloudiness initially. But the chances of tstorms in the afternoon and early evening expand to all of the high desert and even parts of the low desert or inland valleys close to the mountains that could receive a drifter tstorm. We`ll adjust time, space and intensity of any chance of precip as needed, but for now, rain intensity doesn`t appear problematic. All this action doesn`t seem to phase the marine layer very much. A similar medium cloud coverage into western valleys will continue each night and morning. Temperatures will be dampened by the higher humidity and cloud cover, but only by a few degrees. The upper low moves into SoCal Friday, then shifts eastward and dissolves Saturday. The chance of precip goes down and is super slight mainly in the higher mountains Saturday. All dry Sunday and beyond as an upper trough in the Pac NW region shifts the flow to the drier southwest across SoCal. And we`ll be back to our regularly scheduled July weather: marine layer clouds into western valleys each night and morning, temps near normal, and dry. && .AVIATION... 161545Z....Coast/Valleys...Low clouds based 1400-1800 ft MSL will scatter to the coast by 17-19Z. Areas of clouds remaining along parts of the immediate coast all day, particularly in San Diego County. Clouds begin to push inland again after 00z with similar bases. Similar inland extent with most of SD/Orange County valleys filling in by 12z. Clouds may push into the western/southern IE with 40% chance of reaching KONT. Mountains/Deserts...Mostly clear skies with unrestricted VIS through this morning. Cumulus near 10000 feet possible over the mountains 18- 01Z. Increasing clouds AOA 15000 feet overnight. && .MARINE... No hazardous marine conditions are expected through Sunday. && .BEACHES... A moderate period south-southwesterly swell (2-3 feet at 15-16 seconds) will generate elevated surf and a high risk of rip currents today and Thursday. Surf of 3-5 feet expected with sets to 6 feet possible, primarily on southerly facing beaches. Swell and surf will begin to lower on Friday. && .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...KW