Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
547 FXUS66 KSGX 221659 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 959 AM PDT Sat Jun 22 2024 .SYNOPSIS... Hot conditions expected for inland areas this weekend into next week across Southern California. 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... At 9 AM, most locations in the lower desert have hit or exceeded the 90 degree mark. Most locations this morning are running at least a few degrees warmer than 9 AM Friday, with some locations in the valleys and mountain foothills 10 to 15 degrees warmer than 9 AM Friday. The only exception is for a few areas closer to the coast, which are running the same or a couple degrees cooler than yesterday. Highs today are expected to hit the upper 90s to 105 degrees in the Inland Empire; 95 to 100 degrees in the San Diego valleys; low 90s for inland Orange County; 90 to 98 degrees below 5000 ft in the mountains; 100 to 105 degrees in the High Desert; and 110 to 114 degrees in the low desert. Widespread moderate to major heat risk is expected 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 temperatures a couple degrees warmer than today along the coast. The moisture increase will also increase the chances of showers and isolated thunderstorms for the area starting late tonight and continuing into Sunday. Guidance still indicates an easterly wave overnight into Sunday, but guidance is now placing the wave further east. As a result shower and thunderstorm chances have trended down for Southern California, especially overnight tonight into early Sunday morning hours (now 5 percent). That being said, the influx of moisture is still expected to increase precipitable water values to 1.75" in the Lower Deserts, 1.25" in the 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 percent chance of thunderstorms. West of the mountains, chances of showers will be 15-20 percent and in the deserts chances are closer to 20-30 percent with a 5-10 percent chance of isolated thunderstorms Sunday afternoon. 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. Next week will be hot in the valleys, mountains and deserts with the ridge of high pressure anchored over the Four Corners region. An Excessive Heat Warning is in effect for the deserts through Thursday evening. Coastal areas will be spared the searing heat by a shallow marine layer. On Friday and Saturday the ridge weakens ahead of a Pacific trough that will bring a few degrees of cooling to the region. && .AVIATION... 221545Z...Coast/Valleys...Low clouds with bases near 1000 feet MSL and tops near 1400 feet will clear back to over the coastal waters today. After 23/0700Z tonight low clouds increasing in coverage with bases around 1000 ft MSL and tops to 1400 ft MSL. Inland spread will be restricted to the coastal areas and the western portions of the San Diego County valleys. Bases could briefly drop below 1000 ft MSL 12Z-15Z. Local VIS 1-3SM on elevated coastal terrain. Low clouds could be erratic as monsoon moisture spreads over the area overnight and into Sunday, so confidence in the timing and low cloud amounts in the TAFs is low-moderate. Tropical moisture is expected to arrive Saturday night through Sunday morning. The moisture is enough with a weak disturbance to bring a threat for widely scattered lightning and brief showers Saturday night through Sunday. Mountains/Deserts...Clear with unrestricted VIS through Saturday. Tropical moisture is expected to arrive Saturday night through Sunday morning. The moisture is enough with a weak disturbance to bring a threat for widely scattered lightning and brief showers Saturday night through Sunday. && .MARINE...Tropical moisture is expected to arrive Saturday night through Sunday morning. The moisture is enough with a weak disturbance to bring a threat for widely scattered lightning and brief showers Saturday night through Sunday. See the Marine weather statement for more information. && .BEACHES... There is a slight chance of thunderstorms Saturday night through Sunday which could produce cloud-to-ground/cloud-to-water lightning strikes. Chances of a lightning strike near any particular beach are currently 20 percent or less Saturday night and Sunday. Rain showers will generally be brief and light to moderate. && .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. Heat Advisory until 8 PM PDT this evening for Riverside County Mountains-San Bernardino County Mountains-San Diego County Mountains. 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...CO AVIATION/MARINE/BEACHES...Small