Monsoonal thunderstorm activity occurred across Southern California from July 22 to July 29, with a major easterly wave producing widespread convection on July 25 and 26. Numerous reports of heavy rain leading to flash flooding and debris flows were received as well as reports of lightning, hail and dust storm.
Every event with a place to put it. 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.
Monsoonal thunderstorm activity occurred across Southern California from July 22 to July 29, with a major easterly wave producing widespread convection on July 25 and 26. Numerous reports of heavy rain leading to flash flooding and debris flows were received as well as reports of lightning, hail and dust storm.
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 Jul 21, 6:54 PM PST, 5 hours 6 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 754 PM PDT Wed Jul 21 2021 .SYNOPSIS... Our summer weather pattern will continue with chances of afternoon thunderstorms in the mountains and deserts each day into early next week. Chances are a little greater on Thursday and again Sunday and Monday. There will be areas of coastal low cloudiness nights and mornings. Temperatures will be above average today, but gradually decrease to below average through the weekend. && .Evening Update... Clouds struggled to produce very little in the way of precipitation across the area today. One of the big reasons was not enough moisture, which can be seen in this afternoon's forecast sounding from Miramar showing a dryer layer near the surface and weaker winds. Similar to previous nights, low clouds will slowly start to fill in parts of the coast, though a bit more pronounced than yesterday. Temperatures will begin to cool a bit into the weekend as an upper level low pressure system makes its way from the east across SoCal. This will bring more mid and high-level cloudiness across the region as well. Chances for showers and thunderstorms will exist in the mountains and deserts each day through early next week. As the upper level low moves over SoCal, it could make things interesting by the weekend into early next week as stated below. .Previous Discussion (120 PM Wednesday)... Much like yesterday, the cumulus clouds over the mountains and deserts this afternoon are struggling to produce showers and thunderstorms. At most, only one or two isolated thunderstorms are expected. Moisture and instability both increase Thursday, allowing for a better chance of afternoon thunderstorms in all mountains and parts of the desert. These look pretty well behaved for formation along ridges first, then drifting into adjacent deserts later. On Friday the moisture decreases, lessening the chance of afternoon thunderstorms. A blob of high level moisture rotates into our region from the east early Saturday. This is associated with a weak upper low, over Texas today, that will move westward under the belly of the main western ridge of high pressure. That high level moisture will bring a lot more higher clouds, but actually serve to stabilize the atmosphere a bit, inhibiting convection and thunderstorm formation. But there's still a small chance. The upper low draws deeper moisture into our region Sunday and Monday for a better chance. Right now the best forecast is for generally no rain west of the mountains or outside of the afternoon windows of time, except the push on Monday could allow some storms to drift westward into the valleys. Confidence is low that something unusual would happen, like widespread showers or thunderstorms west of the mountains. However, these easterly waves can morph and move around in unpredictable ways that can dramatically change the forecast. We'll monitor the situation closely. The upper low deepens along the West Coast next week, which would turn down the monsoon moisture volume next Tuesday and Wednesday. Today's guidance seems to agree pretty well on this. That will mean dry and warmer weather then. && .AVIATION... 220245Z...Coast/Valleys...SCT-BKN008-012 along the coast extending a few miles inland through 16Z Thursday, occasionally impacting KSAN, KCRQ and KSNA before clearing. Elsewhere...SCT-BKN100-200. Mountains/Deserts...SCT-BKN100-200 through Thursday with SCT TSRA over the mountains from 18Z Thursday through 03Z Friday. && .MARINE... No hazardous marine conditions through Monday. && .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...APR/MM AVIATION/MARINE...Moede
The Santa Ana Mts radar (KSOX), 61 km away, was scanning. The volume nearest the first event began at 07:55 UTC.
13 heavy rain, 5 flash flood, 4 flood. Local standard time, as filed.
Table of rainfall amounts over 7 days across the El Dorado and Apple Burn Scars. Three locations received over 1 inch in 7 days.
Heavy rain of 0.5 inch. Spotter report of a heavy downpour near Jacumba for 10-15 minutes with 2-3 inches of water on the patio, and about 2 feet of water on sections of the dirt road leading to his home.
Flooding at intersection of Dillon Road and Thousand Palms Canyon Road with 200 foot section of roadway washed out.
Between 1:20 and 2:10 am, station ar854 received 0.60 inch of rain.
Desert Sun photo of mud and water covering Vista del Sol and Ramon Road in Thousand Palms. This area received heavy rain 3 to 6 am. Nearby Cathedral City site reported 0.52 inches in 1 hour.
Radar estimated 2 to 2.5 inches of rainfall at the mouth of Box Canyon which caused flash flooding at the entrance of Box Canyon Road and along Painted Canyon Road. There were a couple vehicles involved with the flooding which caused a road closure. Located south of I-10 and north of Highway 111.
Mesonet station au239 Rialto 1. Between 2 and 3 am received 0.35 inches.
One vehicle swept off the roadway on box canyon road with 10 to 12 other vehicles potentially stranded.
Cathedral Canyon raws had 0.42 rainfall in 1 hour and 0.69 inches total.
Palomar Mountain raws had 0.49 inches in 1 hour. 0.96 total so far.
Caltrans reports boulders in the roadway near Vista Point on SR 74.
Damage and washed out section of concrete sidewalk as embankment gave way to flooding along Country Club Drive and Avenue 42. Water covered roadway on Jefferson Street. Photos shared by emergency management. Rain of 0.70 inch per hour observed.
Riverside Emergency Management reported minor rock slide on Highway 111 at Windy Point. Rain gauges showed 0.50 in 30 minutes early that morning.
Mesonet weather station reported 0.89 inches of heavy rain.
Whitewater raws received 1.17 rainfall and 0.53 in 1 hour at 6 am.
Flooding on Varner road near Bermuda Dunes.
San Jacinto raws received 1.44 inches of rain and 0.89 in 1 hour between 5 and 6 am.
CoCoRaHs station CA-SD-195 Valley Center 10.9 NE reported 1.54 inch of heavy rain.
CoCoRaHS station CA-RV-72 Palm Desert 2.1 ENE reported 0.81 inch of heavy rain.
Mesonet station WWAC1 Whitewater raws reported 1.23 inch of heavy rain.
CoCoRaHS station CA-RV-79 La Quinta 0.9 WNW reported 1.52 inch of heavy rain.
Avenue 50 at Tyler Street closed at 1 pm due to water flowing over the road, per phone conversation with emergency manager. This is in the Whitewater Wash, a road designed to flood.
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, July 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: 976741, 975197, 976675, 976674, 976672, 976676, 976696, 975194, 976689, 976692, 976699, 976704, 976705, 976706, 976709, 975196, 976707, 976710, 976711, 976712, 976716, 976720.