Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
880 FXUS66 KSGX 190330 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 830 PM PDT Tue Jun 18 2024 .SYNOPSIS... Warming conditions are expected into this weekend, with above average high temperatures prevailing for much of the area. This period of above average temperatures is expected to continue into the middle part of next week. The marine layer will reach into portions of the valleys each night and morning through Friday, before becoming shallower for this weekend into early next week remaining mostly confined to the coast. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This evening, low clouds are returning to the coastal areas and will likely spread inland to the valleys by early Wednesday morning. A weak upper level disturbance embedded in the mean cyclonic flow aloft could bring some variable mid and high clouds tonight into Wednesday. From previous discussion... High temperatures Wednesday and Thursday are expected to be fairly similar to high temperatures today with a few degrees of fluctuation. By Friday, widespread warming is expected across the area, with hot conditions continuing into Saturday and Sunday. The marine layer will stay 2000 to 2500 feet deep through Friday, with night and morning coastal low clouds extending into portions of the inland valleys late each night. The marine layer will get shallower for the weekend into early next week, becoming more confined to coastal areas, as an area of high pressure builds aloft. High pressure building over the desert southwest will expand west into Southern California Friday into Saturday bringing additional warming. The high pressure system will remain parked over the Southwestern United States through the middle of next week, maintaining above average temperatures across the area. The marine layer will become shallower under the high pressure, allowing the Inland Empire, San Diego valleys, inland Orange County, and the mountain foothills (below 5000 ft) to warm 7 to 10 degrees above average Saturday and Sunday. Saturday currently looks like the warmest day of the weekend, with areas of moderate to locally high heat risk in and west of the mountains. Widespread moderate heat risk will maintain for areas in and west of the mountains Sunday. Folks should avoid strenuous outdoor activities if they can and stay hydrated. For Sunday into early next week, there is still some uncertainty in the placement and amplitude of the high pressure but current forecast indicates a few degrees of cooling for inland areas in and west of the mountains, although temperatures will remain 3 to 7 degrees above average. The deserts, particularly the lower deserts will remain under the influence of the high pressure system into the middle of next week, resulting in a prolonged period of high temperatures 6 to 10 degrees above average. Areas of moderate to high heat risk are expected in the deserts Saturday through at least Tuesday. It looks like the ridge of high pressure will allow for moister to sneak into the deserts from the south/southeast which introduces some uncertainty into the high temperature forecast. ECMWF ensemble guidance is indicating the mean precipitable water values for Thermal will be above an inch Saturday into early next week. The moisture looks to be mostly focused in the mid-levels, so precipitation chances remain less than 10 percent at this time with the most likely impact being an increase in high cloud coverage. Current temperature forecast follows the NBM for the Saturday through Tuesday time frame. && .AVIATION... 190330Z...Coast/Valleys...Low clouds moving ashore at this hour with bases around 1700 ft MSL and tops to 2200 ft MSL. Low clouds likely spreading 15-20 mi inland by 14Z, obscuring higher terrain with VIS locally 1-3SM where clouds and terrain intersect. CIGs unlikely to go below 1500 ft MSL, with CIG impacts likely at coastal TAF sites 06Z-17Z. 55-65 percent chance for CIG impacts at KONT and KSBD 10Z- 16Z. Expect clearing to the coast 16Z-18Z Wednesday. Mountains/Deserts...FEW-SCT at or abv 20000 ft MSL with unrestricted VIS through Wednesday. West winds with gusts near 25 kts below the San Gorgonio Pass this evening. && .MARINE... No hazardous marine weather conditions are expected through the weekend. && .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...CO/PG AVIATION/MARINE...PG