Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
205 FXUS66 KSGX 230415 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 915 PM PDT Sat Jun 22 2024 .SYNOPSIS... Hot conditions expected for inland areas this weekend, with heat continuing into next week for the deserts. A moisture surge tonight and Sunday will increase the humidity and bring a slight chance of showers and isolated thunderstorms to most areas. The best chances of measurable rainfall and thunderstorm development is in the mountains Sunday afternoon. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Evening Update... Our sounding this evening shows more moisture present around 600mb and PWAT values near 1.40", about double from this morning`s launch. Mid-level clouds are seen moving up from the south this evening over northern Baja into Arizona, while marine layer clouds push slightly east near San Clemente Island. Most clouds should stay out of the region tonight, with increasing clouds by the morning hours. Forecast changes this evening include lowering chances for thunderstorms for areas west of the mountains tonight as the environment is still a bit too dry to support any measurable precipitation. Sunday still looks like the most active day with moisture and instability in place. Best chances will be across higher terrain into adjacent deserts, though latest hi-res models have backed off on precip, indicating isolated activity mostly over higher terrain. Chances on Monday continue to remain minimal, mainly across the San Bernardino Mountains. As stated below, it will be a hot and humid day tomorrow for much of Southern California. Stay safe in the heat by wearing sunscreen, drinking plenty of water, and taking breaks if outdoors! .Previous Discussion (150 PM Saturday)... Widespread moderate to major heat risk continues away from the the coast this weekend. Please be mindful if venturing outdoors for recreation this weekend. Drink plenty of fluids and if possible avoid strenuous outdoor activity between 10 am and 5 pm, or take frequent breaks. A surge of moisture Sunday will knock temperatures down a few degrees for inland areas and disrupt the marine layer resulting in a couple degrees of warming along the coast. The increase in humidity will make it harder to keep cool, even if the official readings are a few degrees below today. The moisture increase will also bring chances of showers and isolated thunderstorms into Sunday. Models are showing our forecast area being on the western edge of the action. As a result shower and thunderstorm chances have trended down for overnight tonight into early Sunday morning hours, with thunderstorm chances around 5 percent. That being said, the influx of moisture is still expected to increase precipitable water values to around 1.50" in the lower deserts, 1.25" west of the mountains and 1" in the mountains Sunday. A weak shortwave coupled with the heat of the day will generate mid-level lapse rates of 7.7C/km Sunday afternoon and raise CAPE values to 500-600 J/kg. Chances for showers and isolated thunderstorms are highest in the mountains Sunday afternoon with a 30-35 percent chance of showers and a 10-15 percent chance of thunderstorms. West of the mountains, chances of showers will be 15-20 percent with isolated thunderstorm chances 5 percent or less. In the deserts shower chances are closer to 20-25 percent with a 5-10 percent chance of isolated thunderstorms. Best chances of accumulating precipitation will be in the mountains, with little to no precipitation expected to accumulate elsewhere. Enough moisture is expected to remain in the atmosphere for isolated convection to again be possible Monday afternoon, mainly over the San Bernardino Mountains and High Deserts. As the ridge remains over the Four Corners region, hot conditions will continue through mid-week, especially in the deserts. Temperatures in and west of the mountains will cool a few degrees each day through mid-week, brining highs near to just below the seasonal average. Coastal areas will keep a shallow marine layer, which will moderate temperatures there. On Thursday, a trough of low pressure moving into the Pacific Northwest will weaken the ridge bringing a few additional degrees of cooling from the coast to the deserts. && .AVIATION... 230400Z...Coast/Valleys...Patchy BKN low clouds with bases 700-1000 ft MSL will occur near the immediate coast 07Z-17Z Sun. Chance of a CIG at KSAN is 40-50 percent. Tops will be 1200 ft MSL, with local VIS 3-5 miles over higher coastal terrain. There is around a 10 percent chance of TS 18Z Sun-02Z Mon, with highest chances in the valleys. Otherwise, SCT-BKN clouds mostly at/above 9000 ft MSL will prevail through Sun evening. Mountains/Deserts...There is a 20-30 percent chance of TSRA 17Z Sun- 04Z Mon, with CB tops to 35000 ft MSL and possible strong up/downdrafts and local surface wind gusts over 30 kt. Otherwise, SCT-BKN clouds mostly at/above 9000 ft MSL will prevail through Sun evening. Local west winds with gusts 25-35 kt will develop after 22Z Sun, continuing Sun evening on the desert mountain slopes and into the deserts and through San Gorgonio Pass. && .MARINE... Tropical moisture aloft will bring a very small chance of thunderstorms (less than 10 percent at any one location) mainly Sunday afternoon. Isolated cloud-to-water lightning strikes will be possible, along with locally gusty winds. Wind gusts could exceed 20 knots in the outer coastal waters Thursday. Otherwise, no hazardous marine conditions will occur through Thursday. && .BEACHES... There is a slight chance of thunderstorms mainly Sunday afternoon which could produce cloud-to-ground/cloud-to-water lightning strikes. Chance of a lightning strike near any particular beach is around or less than 10 percent Sunday afternoon. Rain showers will generally be brief. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory until 8 PM PDT Sunday for Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Valleys. Excessive Heat Warning until 8 PM PDT Thursday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts- San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC...APR/CO AVIATION/MARINE...Maxwell/Zuber