A closed upper-low pressure system produced widespread measurable rainfall across Southern California, breezy winds across the mountains and deserts and record low high temperatures.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
A closed upper-low pressure system produced widespread measurable rainfall across Southern California, breezy winds across the mountains and deserts and record low high temperatures.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Diego, CA wrote its last area forecast discussion before the first event at May 14, 7:52 PM PST, 4 hours 8 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 852 PM PDT Fri May 14 2021 .SYNOPSIS... A low pressure system from the northwest will move slowly across California this weekend. This system will bring cooler weather, along with gusty westerly winds across our mountains and deserts. The marine layer will slowly deepen and generate patchy drizzle or light rain showers at times, and fog on the coastal slopes of the mountains. Warmer and drier weather will develop early next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Marine clouds cleared the coast again by afternoon, but began filling back in from the south by 3 PM. At 7 PM PDT...the large area of the California Bight that had cleared earlier, was rapidly filling in and the clouds were spreading rapidly inland this evening. Our 00Z Miramar sounding had a 6.5C inversion based near 2500 FT and winds wee light and variable below 6K FT. Onshore sfc pressure gradients were strengthening and supporting strong and gusty winds again, mainly near the passes. Strongest were near the San Gorgonio Pass at 25-30 MPH with gusts nearing 50 MPH. No forecast changes this evening. From previous discussion... Expect patchy drizzle late tonight and Saturday morning. A low pressure trough will deepen today over Oregon and dive south through California this weekend. It will enhance the marine layer, extending clouds even farther inland and up the mountain slopes. A coastal eddy circulation will develop to assist that process. Cooler air aloft will replace the hot desert air in cold front fashion. Temperatures near the coast won't change much, but they will fall inland, especially in the deserts over the weekend. By Sunday, the upper trough will be over California, and max temps will be in the 50s in the mountains, 60s and lower 70s in the coastal basin, lower 70s in the high desert and 80s in the low desert. Yes, it will be that cool. Cloud coverage will be similar, filling at least the coastal basin each night and morning. Coastal areas may struggle to clear fully on Saturday, while inland areas will struggle to clear fully Sunday. Winds will pick up in the mountains and deserts during the afternoons and evenings Saturday and Sunday with the trough passage. Right now they don't appear hazardous, with top gusts in the favored mountain passes 40-50 mph. Actual light rain showers are possible early Sunday morning, but then the chance of showers appears to migrate inland into foothills later Sunday into the evening. Total precipitation will be less than one tenth inch, but locally higher in foothills. The trough moves out Monday, so the deep marine layer will begin to tamp down Tuesday into Wednesday. High pressure aloft will bring warmer weather, with temperatures closer to normal by midweek, and the marine layer and its cloud coverage a little more confined and less monstrous. Ensembles indicate a western trough deepening Wednesday or Thursday, and differ on exact timing and strength. Either way, we'll flip the see- saw back toward the cooler, cloudier solution, just not as profound as this weekend's outcome. Enjoy the May Gray. && .AVIATION... 150315Z...Coast/Valleys...OVC018-023 tops 028 filling in all areas west of the mountains through 14Z Sat. Areas of vis 2-4 miles in FG/HZ in the eastern valleys through 19Z where clouds and terrain intersect. Clearing from inland back to the coast 17Z-21Z. Mountains/Deserts...Mostly clear with unrestricted vis through Saturday. && .MARINE... No hazardous marine weather is expected through Tuesday. && .BEACHES... A long period south swell from 200 degrees will arrive late Saturday and peak Sunday morning at 3 ft/17 sec. This will produce elevated surf of 4-6 ft on south-southwest facing beaches of Orange County and far northern San Diego County. Strong rip and longshore currents are likely at most beaches Sunday into Monday. Swell and surf lower through the day Monday. Another south swell arrives late Tuesday and peaks Wednesday for another round of elevated surf and a high risk of rip currents. && .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...10 AVIATION/MARINE/BEACHES...Moede
The national radar mosaic for the moment the first event began.
1 heavy rain, 1 high wind. Local standard time, as filed.
CRR1 Paivika Ridge (elevation 5298) reported a 48 hour precipitation amount of 0.84 inch.
Strong westerly winds impacted the San Gorgonio Pass from mid-morning on May 15 through the early-morning hours on May 17. Widespread wind gusts of 40-65 mph occurred. The highest wind gust of the event occurred near Whitewater, where a 72 mph wind gust was reported at 0140 AM on May 17.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, May 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 960644, 960639.