397 FXUS66 KSGX 161557 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 857 AM PDT Mon Jun 16 2025 .SYNOPSIS... Hot conditions look to continue through Wednesday for inland locations. Gradual cooling expected Thursday into the weekend. Patchy night and morning low clouds and fog are expected tonight into Tuesday along the coast, with more widespread cloud coverage that will gradually increase in depth Wednesday through the weekend. Breezy west winds across the mountains and deserts each afternoon and evening, strongest today. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Hot conditions will continue today for inland areas, with temperatures at 9 AM already running 3 to 7 degrees warmer than this time yesterday for most locations. Widespread moderate HeatRisk will impact the inland valleys, mountain foothills, and High Desert today, with moderate to locally major HeatRisk in the low desert. Make sure you`re staying hydrated and seeking shade if you`re spending time outdoors. If possible, avoid strenuous outdoor activity during the hottest part of the day (through 5pm). Most model guidance is showing minimal changes in high temperatures between today and Tuesday for inland Orange County, San Diego valleys, and mountains. For inland Orange County and portions of the San Diego valleys, how much marine layer cloud coverage develops overnight will have an impact on how hot it gets Tuesday. Currently, high resolution guidance keeps low cloud coverage quite patchy overnight, so the forecast has been updated and is trending towards the hotter end of the guidance. For the Inland Empire, temperatures will see minimal changes through Wednesday, keeping highs between in the upper 90s to just over 100 degrees. A very gradual cooling is expected in the deserts for Tuesday into the weekend. The exception is the High Deserts are expected to see a degree or two of warming on Wednesday, before continuing their cooling trend. Widespread moderate HeatRisk will continue through Thursday for the High Desert and Friday for the low desert. A passing weak area of low pressure will move across central California today, which will strengthen the onshore pressure gradient. That will bring breezy west winds to the desert mountain slopes, below the passes, and into the deserts during the afternoons and evenings. Strongest winds are expected today with gusts 30 to 45 mph, locally up to 50 mph through the San Gorgonio Pass. Ensemble guidance is in good agreement that the ridge of high pressure will get pushed east ahead of an incoming low pressure system approaching the Pacific Northwest. That will bring widespread cooling, a deeper marine layer, and increased winds over the mountains into the deserts. Marine layer low clouds and fog are expected to reach well into the valleys by the end of the week. There is high confidence in dry conditions with this passing trough. Near average temperatures will return by Friday, with below average temperatures expected through the weekend. && .AVIATION... 161530Z....Coast/Valleys...Except for patchy low clouds along immediate coast through 19Z, conditions will be mostly clear and VFR today through the evening. Areas of low clouds will redevelop and push ashore after 04Z, but only into westernmost valleys overnight. Bases will be around 400-600 feet MSL with widespread vis 2-5SM, but near zero over higher coastal terrain and western valleys. Scatter out Tuesday 15-16Z. .Mountains/Deserts...Clear skies and unrestricted vis through Tuesday morning. West winds 21-08Z with gusts 20-30 kts, locally near 40 kts through the San Gorgonio Pass, leading to MOD UDDFS. && .MARINE... Wind gusts up to 20-25 kts possible in the outer waters this afternoon and evening near San Clemente Island. Otherwise, no hazardous marine conditions are expected through 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...CO AVIATION/MARINE...MM