086 FXUS66 KSGX 231020 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 320 AM PDT Tue Apr 23 2024 .SYNOPSIS... A cooling trend will continue through Thursday with periods of stronger and gusty southwest to west winds continuing for the mountains and deserts into Friday evening. A deep marine layer will continue into Friday with some light precipitation from drizzle or light rain possible from the coast to the coastal slopes of the mountains, mostly during nights and mornings. Then warmer and drier with weaker winds for Saturday through Monday with Sunday high temperatures around average and Monday high temperatures around 5 degrees above average. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Thursday)... A low pressure system to the west of the area will move inland through southern California on late Wednesday and Wednesday night with stronger onshore flow continuing into Friday night as a second low pressure system from the northwest moves through southern California some time around Friday. The marine layer has deepened to around 4000 feet with an extensive low cloud field over the coastal waters extending inland across all of the valleys and onto the lower coastal slopes of the mountains. There were areas of drizzle late Monday evening as the depth of the saturated cloud layer increased to around 2500 feet versus around 800 feet late Monday afternoon. The greatest concentration of light measurable amounts has been over the western valleys in San Diego County and for inland Orange County onto the coastal slopes of the Santa Ana Mountains. This deep marine layer will continue into Friday with chances for measurable precipitation from drizzle or light rain, mainly during the nights and mornings. Periods of gusty southwest to west winds will continue for the mountains and deserts into Friday evening with the stronger winds along and below the desert slopes of the mountains in Riverside and San Diego Counties. ECMWF ensemble output shows the winds gradually increasing each day into Friday with the strongest winds on Friday afternoon. With the gradual strengthening, the winds could be strong enough for a Wind Advisory as early as Wednesday afternoon and evening. High temperatures for inland areas will cool each day through Thursday with Thursday high temperatures around 5 degrees below average near the coast to 10 to 15 degrees below average for the mountains and valleys. && .LONG TERM (Friday through Monday)... After Friday, there will be warming and drying for Saturday through Monday with weaker winds. High temperatures will warm each day to around average on Sunday and around 5 degrees above average on Monday. && .AVIATION... 230930Z...Coast/Valleys/Foothills...Low clouds with bases 1500-2500 feet MSL, locally down to 1000 feet in -DZ, and tops to 4000 feet. VIS 0-5SM inland, where clouds and terrain intersect obscuring foothills. Expect inland clearing 17-19Z with only partial clearing in the coastal areas. CIGs around 2000-3000 feet could impact coastal airports through afternoon. Low clouds to push inland and fill the coastal basin to foothills again after 01Z into early Wednesday. Similar bases and inland vis reductions. Mountains/Deserts...Mostly clear skies (above 4000 feet MSL on coastal slopes) with unrestricted VIS today and tonight. && .MARINE... No hazardous marine conditions are expected through Thursday. Stronger northwest winds and choppy seas arrive late Thursday and continue into early Saturday, likely generating hazardous conditions at times, especially in the outer waters. && .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...17 AVIATION/MARINE...MM