@ FXUS66 KSGX 192131 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 231 PM PDT Tue May 19 2026 .SYNOPSIS... High temperatures for the mountains and deserts will warm through Thursday. High temperatures for the coast and valleys will warm several more degrees today, then slowly cool into next weekend. Night and morning coastal low clouds will return and increase in coverage during the middle of the week, then spread farther into the inland valleys by next weekend. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Thursday)... As of 2:00 PM PDT, satellite depicts mostly clear skies with an isolated patch of cirrus clouds. Temperatures are running 5 to 10 degrees warmer than yesterday inland, reaching into the mid-to-upper 80s through the Inland Empire and the upper 70s/low 80s for inland areas of San Diego and Orange Counties. Most of the lowlands are experiencing a typical May sea breeze. The San Diego to Tonopah pressure gradient has remained constant at around -5 mbs, yielding to offshore flow (N/NE winds) and lower humidity through most of the Inland Empire and in the mountains. As a result, relative humidities are 10-20% in the mountains and 15-30% through the Inland Empire. The sea breeze boundary will push eastward through the foothills and mountains this afternoon, increasing humidities this evening through the boundary layer - below 3000-400 feet elevation. This morning's sounding showed a marine layer thickness of around 2500 feet deep, and with similar 700-mb heights, the marine layer should settle to a similar depth tonight, where humidities will mostly recover above 50% overnight (80% closer to the coast). Clouds will struggle to develop, however, and should be restricted to coastal San Diego County should any clouds develop (65-75% chance). While 500-mb heights don't change much, the weak surface high pressure in the Great Basin creating offshore flow will continue to move eastward. Temperatures will warm in the deserts through Thursday, which will increase the onshore pressure gradient and enhance the sea breeze. The marine layer will gradually deepen each day, with higher chances for more broad coverage into the Inland Empire Thursday morning. While there isn't a strong temperature trend this week, temperatures peak Wednesday for inland areas (mid-80s - low 90s) and Thursday through the low deserts (approaching 100 degrees). && .LONG TERM (Friday through Monday)... Temperatures in the mountains and deserts look to remain relatively constant through next Monday. At the coast and through the inland valleys, temperatures look to gradually decrease a degree or two each day through Sunday, with perhaps a steeper decrease in temperatures Monday onward, contingent upon a trough digging deep from the Pacific Northwest into Southern California. Based on WPC 500-mb clusters, about 30% of ensemble runs are converging on this solution, while others build a ridge to the northwest, though keeping heights above Southern California around normal for this time of year. && .AVIATION... 191700Z...Mostly clear skies expected through early Wednesday morning. Offshore breezes with strongest gusts 20-25 kts through mountain passes and foothills will diminish within the next few hours. 30-70% chance for low clouds based 1000-2000 ft MSL over coastal San Diego County after 11z (highest chances near KSAN). Low clouds will scatter to the coast by 16-17z Wed. && .MARINE... West-northwest winds will gust to near 20 kts over outer coastal waters this afternoon and evening. Otherwise, no hazardous marine conditions are expected through Sunday morning. && .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...Westerink AVIATION/MARINE...KW