An early monsoonal moisture push occurred during the middle of May across Southern California. The heaviest activity occurred in the High Desert, where several reports of flooding were documented.
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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.
An early monsoonal moisture push occurred during the middle of May across Southern California. The heaviest activity occurred in the High Desert, where several reports of flooding were documented. Hot and humid conditions also occurred region-wide.
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 20, 1:14 PM PST, 4 hours 49 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 214 PM PDT Sat May 20 2023 .SYNOPSIS... Persistent low clouds will occur each night and morning across the coast and valleys through next week, with minimal clearing for the coast each day. Thunderstorms will be possible over the mountains and deserts each afternoon through Monday, with the most widespread activity occurring today. Longwave troughing returns early next week, with cooling, a deepening marine layer and drier conditions expected. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Scattered thunderstorms are anticipated mainly over the San Bernardino Mountains and High Desert area from late this afternoon through middle evening. Activity over far Northeastern San Bernardino continues to progress southwest towards the San Bernardino Mountains this afternoon and we anticipate outflow from that cluster of thunderstorms to reignite convection late this afternoon along the upslope north portion of the mountains including the Big Bear area. Daytime heating will contribute to moderately conducive conditions for updrafts but again easterly wind shear will be difficult to combat at least with the initial convection. Thus the best chance of showers and thunderstorms will be late afternoon through mid- evening across the mountains. The latest HRRR is targeting the San Bernardino Mountains and the High Desert for the best chances, as well, and that makes sense given the better heating and less debris cloud cover. Good storm movement should limit torrential downpours although some training is possible due to the persistent storm motion. Instability is also maximized over San Bernardino County this afternoon, with lesser indices over the Riverside Mountains, and especially in San Diego County which was limited earlier today by debris cloudiness from nocturnal convection ended earlier this morning. The debris clouds could limit instability over the San Diego County Mountains but could help to scour out some of the low clouds near the coast as previous mornings. Convection will die off by late this evening, certainly most activity before midnight, with the late convection today should preclude nocturnal convection tonight until perhaps very late in the evening. For Sunday afternoon and evening, remnant boundaries, diurnal heating and persistent mid-level moisture will contribute to another round of scattered showers and thunderstorms once again. The chances for convection on Sunday will be very similar to today, most likely. Long Term Discussion: Lesser chances for convection on Monday due to declining instability and mid level moisture advection, with the pattern finally shifting to a drier westerly flow for Tuesday onward. A baggy trough will settle over SoCal for mid to late next week, bringing a healthy onshore flow each day, but otherwise benign weather and slightly cooler conditions for inland areas, should be expected through the end of next week, with good continuity in the ensemble and deterministic forecasts. && .AVIATION... 202030Z...Coast/Valleys...Areas of BKN/OVC low clouds will continue this afternoon within 5-10 miles of coast with bases 1300-1700 ft MSL with tops to 2200 ft MSL. BKN/OVC low clouds with similar bases/tops will spread to 10-15 miles inland 00Z-04Z Sun and eventually through most valleys by 10Z Sun, with higher terrain obscured at times and local VIS below 1 mile in BR/FG in the valleys. Clearing will occur 16Z-19Z Sun except for areas of stratus lingering within 5 miles of the coast Sun afternoon. Mountains/Deserts...ISO-SCT TSRA will occur through 04Z Sun over the mountains and deserts, with greatest coverage in San Bernardino County. CB bases will be 9000-10000 ft MSL and tops to 35000 ft MSL. Otherwise, SCT-BKN clouds at/above 10000 ft MSL will prevail with mostly unrestricted VIS. There is a chance of TSRA in the mountains and deserts again Sun afternoon. && .MARINE... No hazardous marine conditions are forecast through Thursday. && .BEACHES... The long-period southerly swell will continue to dissipate this afternoon, with most surf below 6 feet. The rip current risk will remain high this afternoon but then decrease Sunday. && .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...Brotherton AVIATION/MARINE/BEACHES...Maxwell
The Edwards AFB radar (KEYX), 52 km away, was scanning. The volume nearest the first event began at 02:05 UTC.
2 flash flood, 1 flood. Local standard time, as filed.
Public report of traffic driving through several inches of moving water along Highway 395 at Desert Flower Road.
Public report (via Waze) of flooding along Highway 18 near Palmdale Road in Phelan. El Mirage Raws (9 miles north) received 1.23 inches of rain between 4:26-5:26 PM.
NWS storm survey conducted by WFO San Diego. Several sections of Mountain View Road were covered in mud as much as two feet deep with damage on the side pavement. El Mirage Raws recorded 1.23 inches of rain during the afternoon on May 21. Radar total estimates of 2-4 inches occurred in surrounding areas. Standing water along El Mirage Road with one home surrounded by water. A nearby dry lake bed was partially water logged.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, May 2023
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: 1106314, 1106316, 1106320.