311 FXUS66 KSGX 301609 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 909 AM PDT Fri Jun 30 2023 .SYNOPSIS... Hot conditions expected for inland areas through the holiday weekend. Along the coast, sea breezes will keep temperatures moderated, along with periods of low clouds and fog. High pressure aloft will weaken early next week, bringing progressive cooling inland. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Key Points: *Hot conditions for inland areas through the holiday weekend. *Cooler at the coast with areas of fog each night and morning. Areas of low clouds from the coast to the western valleys are dissipating on visible satellite this morning with mostly clear skies expected for most locations by later this morning. Some low clouds may linger along the immediate coast into this afternoon. High temperatures today are expected to be quite a few degrees warmer than yesterday, most noticeably in the Inland Empire, mountains, and deserts. Along the coast, highs are expected to be up to 5 degrees warmer than yesterday. Hot conditions will continue through the holiday weekend. Major heat risk expected in the deserts and locally in the mountains through Monday. Widespread moderate heat risk expected for the Inland Empire through Monday. Locally moderate heat risk expected in the eastern San Diego valleys. High temperatures will start to decrease for areas west of the mountains by Tuesday but summer will be in full swing for the deserts with moderate heat risk continuing into next week. Coastal areas will not be as influenced by the heat this weekend due to a shallow marine layer locked in place by a strong inversion. Sea breezes will continue to transport ocean-cooled air inland along the coastal plain, and we may even have some difficulty completely clearing beach areas of the low clouds/fog some days. Cooler conditions could return to the valleys west of the mountains as early as the Fourth of July as the ridge over the West Coast begins to weaken. Most global guidance is in agreement that cooling will occur, but there is a lack of agreement when it comes to the degree of cooling. Based on the NBM, most inland areas should experience noticeable cooling for the latter half of next week, with some troughing along the West Coast. && .AVIATION... 301515Z...Coast/Valleys...BKN-OVC stratus with bases 700-1400 ft MSL continue to overspread areas 15-20 mi inland with local vis 3-5 SM in BR/HZ where clouds approach or intersect terrain. Stratus clearing to the coast 17-19Z. Clouds redeveloping at the coast 01/00- 03Z with bases 500-1000 ft MSL, spreading 10-15 mi inland overnight. More widespread lower vis of 2-4 SM, locally 1 SM or less, likely tonight into Sat morning, especially over elevated coastal terrain. Mountains/Deserts...Mostly clear with unrestricted VIS through Saturday morning. && .MARINE... Patchy fog is possible over the coastal waters each night into mid morning Saturday through Tuesday. && .FIRE WEATHER... Elevated wildfire potential through the passes and into the deserts through the forecast period. Gusty westerly winds, low RH, and heat will create an environment that is more susceptible to fire starts and spread. A shallow marine influence will keep relative humidity from reaching critical levels along the coastal slopes and into the valleys. Excessive heat, gusty afternoon sea breezes, and the abundance of cured, finer fuels still poses an elevated wildfire threat. Should ignition occur, large, plume-dominated fires will be possible. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for Riverside County Mountains-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains. Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC/FIRE WEATHER...CO AVIATION/MARINE...Adams