FXUS66 KSGX 191051 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 351 AM PDT Tue Aug 19 2025 .SYNOPSIS... A warming trend is expected this week with less marine layer cloud coverage. It will be hot inland through the weekend, with Thursday and Friday as the hottest days. Monsoonal moisture will increase for Thursday into the weekend with increasing chances for showers and thunderstorms, especially for the mountains and deserts during the afternoons and early evenings. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Thursday)... Strengthening high pressure over the southwest states and Great Basin will bring warming through Thursday and Friday with Thursday high temperatures 4 to 8 degrees above average for inland areas. High temperatures on Thursday will range from the 70s near the coast to the mid 90s to 106 for the Inland Empire with 110 to 116 for the lower deserts. The most likely locations to near or exceed daily records for high temperatures and warmest overnight low temperatures are in the mountains for Thursday and Friday. Satellite imagery shows low clouds becoming widespread across the inner coastal waters of Orange and San Diego Counties. The low clouds will continue to spread slowly inland through sunrise, covering much of the Orange County coastal plain and in San Diego County extending inland into the far western valleys. Monsoonal moisture will begin to increase on Thursday with a slight chance for afternoon showers and thunderstorms for the mountains and high desert. && .LONG TERM (Friday through Monday)... Monsoonal moisture will continue to increase into the weekend with ensemble guidance having precipitable water values greatest over the weekend with little spread in values among ensemble members. Chances for showers and thunderstorms will increase into the weekend, especially for the mountains and deserts during the afternoons and early evenings. For Big Bear, NBM daily chances for measurable rainfall are greatest on Saturday at 73 percent followed by 68 percent on Sunday. Daily chances for one-half inch or more of rainfall for Big Bear are greatest on Sunday at 20 percent. Nights will remain warmer through the weekend with days not quite as hot by Sunday and Monday as moisture and cloud cover from monsoonal convection increases. && .AVIATION... 190930Z...Coast/Valleys...While a bulk of cloud cover has remained offshore overnight, patches of clouds are now forming along the immediate coasts this morning (09z Tuesday), with bases around 700- 1100ft MSL. Coverage will likely remain patchy through the remainder of the morning, and while brief scattering may occur at times, generally BKN-OVC CIGs expected along the coasts. VIS reductions to 3-5 SM in BR for higher coastal terrain. Any clouds will scatter back out by 16-17z, with clear skies and VFR conditions prevailing throughout the day. Low confidence in any low clouds reforming after 00z Wednesday...with only a 30-50% chance of CIGs along coastal San Diego County by 12z Wednesday. Mountains/Deserts...VFR conditions prevailing through early Wednesday. Increasing high level clouds ~15-20k ft MSL through the day today. && .MARINE... No hazardous marine conditions are expected through Saturday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Extreme Heat Watch from Thursday morning through Saturday evening for Apple and Lucerne Valleys-Coachella Valley-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Deserts-San Gorgonio Pass near Banning. Extreme Heat Watch from Thursday morning through Friday evening for Orange County Inland Areas-Riverside County Mountains- San Bernardino County Mountains-San Diego County Mountains- San Diego County Valleys-Santa Ana Mountains and Foothills. PZ...None. && $$ PUBLIC...17 AVIATION/MARINE...Munyan