Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
989 FXUS66 KSGX 192059 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 159 PM PDT Thu Sep 19 2024 .SYNOPSIS... A low pressure system moving southward into the region will bring cooler and showery weather by tonight into Friday. There is a chance for rain showers across most of the region, with a chance for thunderstorms from the Santa Ana mountains to the high desert. The system will depart the area by the weekend, bringing drier weather with warming temperatures. Weak high pressure will then build into the region brining near to slightly above average temperatures with night/morning low clouds near the coast. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM...(Through This Weekend)... A 570 mb upper level low pressure system is currently moving into Southern California this afternoon. This system will continue the cooler than average weather pattern through Friday, where much of the area has a chance for showers and thunderstorms. Low clouds will begin to build back into areas west of the mountains as the marine layer becomes deeper. As the low moves closer to SoCal, expect light showers and marine layer drizzle across for areas west of the mountains to begin late tonight, highest confidence over San Diego County; HRRR agrees with this thinking as the southern end of the low crosses over. Instability peaks near 200-400 J/kg by Friday. Wrap-around moisture from the north will bring elevated showers and isolated thunderstorms by Friday afternoon. Most areas will see dry weather or light showers with the best chance of thunderstorms occurring from the Santa Ana mountains to the Inland Empire northward toward the SBD mountains and high desert. Rain rates will near one quarter to below one half inch, so please continue to monitor this if you are near any recent burn scar locations. Rain totals will be light outside of areas mentioned with storms, where most will receive none to under one tenth of an inch. The system will depart by Saturday, leading to warming temperatures and sunnier conditions. Sunday will warm further as weak high pressure moves into the area with highs reaching near 90 degrees for inland valleys west of the mountains into the high desert. Mountain locations will rise into the 70s and 80s with near 100 degrees for the lower deserts. && .LONG TERM...(Next Week)... The ridge near the West Coast for the weekend will grow and amplify across across the west. The good news is that this will be strongest across the Pacific Northwest, with a weaker ridging pattern near our area. This will prompt temperatures to be near to slightly above average for the much of the week. The marine layer will be generally unchanged with night and morning low clouds to cover most coastal and western valley areas. Ensemble cluster models indicate a potential trough over the Pacific Northwest may be able to tamper down the high pressure a bit further by later next week. This would not change our weather pattern very much with continued dry and slightly above average temperatures. && .AVIATION... 192030Z...Coast to mountain slopes...Low clouds have generally eroded out of San Diego County this afternoon, but are lingering in Orange and western Riverside/San Bernardino counties. Varying bases at 3200-4200 ft MSL and tops to 4000-5000 ft MSL. Clouds will continue to scatter out through about 00Z, before low clouds become more widespread, filling the entire coastal basin again 01-09Z, with similar bases and tops. Patchy, intermittent -RA or -DZ most likely along the coast and up against the coastal mountain slopes after 06Z Friday through the period, which would reduce vis 4-6 SM and lead to locally lower cigs. There is also a 15-20% chance for thunderstorms over the eastern Santa Ana Mtns and Inland Empire after 18Z Fri. Cig heights may vary frequently as a low pressure system moves over the region. Mountain ridges to deserts... SCT high clouds today and tonight. 20- 35% chance for showers and thunderstorms after 18Z Fri over mountains and deserts, most likely over the mtns of San Bernardino and Riverside counties as well as the high desert in San Bernardino County. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .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...APR AVIATION/MARINE...CSP