An upper level storm system coming from the Eastern Pacific interacted with monsoonal moisture on September 1, 2023. The interaction of these features led to the development of heavy rain and thunderstorms, which caused several instances of flooding in the Coachella Valley.
Every event with a place to put it; 2 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.
An upper level storm system coming from the Eastern Pacific interacted with monsoonal moisture on September 1, 2023. The interaction of these features led to the development of heavy rain and thunderstorms, which caused several instances of flooding in the Coachella Valley. Some instances of blowing dust were also observed.
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 Sep 1, 8:42 AM PST, 3 hours 18 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
942 AM PDT Fri Sep 1 2023
.SYNOPSIS...
Areas of thunderstorms in the deserts and mountains with heavy rain
and gusty winds are expected this afternoon and early evening.
Thunderstorms are most likely in the lower deserts and on the desert
mountain slopes. Areas of showers are possible at times into early
Sunday, even for areas west of the mountains. Drier southwest flow
aloft will develop on Sunday and Monday. There will be a gradual
warming trend for next week with the marine layer becoming
shallower.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Key Points:
*Heavy rain and flooding possible in portions of the lower deserts
this afternoon.
*Chances of shower and thunderstorms possible at times through
Sunday morning.
*Areas of gusty south to southwest winds expected in the mountains
and deserts into early Saturday.
Precipitable water values over and inch and surface based CAPE
between 500-2000 j/kg over the lower deserts, combined with mid-
level instability will create an environment conducive for
thunderstorms, heavy rain, and gusty winds today. Rainfall rates
could reach 0.75 to 1 inch per hour in the lower deserts this
afternoon and early evening. A Flood Watch has been issued for the
Coachella Valley and San Diego County Deserts for 12pm today
through this evening. Areas of heavy rainfall are possible in the
mountains as well, most high resolution guidance has the heaviest
rain on the desert mountain slopes. Additionally, periods of
gusty south to southwesterly winds are possible over the mountains
and deserts into early Sunday. The strongest winds are expected
in the San Bernardino mountains into the High Deserts, with peak
gusts around 50 mph.
For areas west of the mountains, isolated showers spurred by the
elevated convection could develop any time into early Sunday. The
unstable atmosphere may hinder the reformation of the marine layer
over the next couple of days, leaving low confidence in any
widespread low cloud coverage through at least late Saturday. Drier
southwest flow aloft will start to prevail Sunday and Monday
resulting in the return of drier conditions.
A weaker trough low pressure will prevail near the California coast
early next week while later in the week high pressure to the east
will strengthen and expand across southern California. High
temperatures around 10 degrees below average for inland areas on
Monday will gradually warm during the week to around average for
Thursday. Drier southwest flow aloft will prevail for much of the
week. The marine layer will become gradually shallower through the
week. Night and morning coastal low clouds and fog will extend
inland into portions of the inland valleys on Monday, then not
extend inland much past coastal areas or the far western valleys by
late in the week.
&&
.AVIATION...
011530Z...Coast/Valleys...SCT clouds around 3000 feet MSL, 12000
feet today. Lower clouds to redevelop and spread back inland after
00Z. Look for multiple layers, the lowest of 1500-2000 feet MSL
near the coast in the evening with additional layers with bases
2500-3500 feet MSL and tops gradually rising to 5000 feet MSL with
isold -SHRA by Saturday morning. In addition to low clouds, there
is a slight (15-20 percent) chance of showers and 5-10 percent
chance of thunderstorms today.
Mountains/Deserts...SCT-BKN clouds at/above 10000 feet MSL and
isolated SHRA, then a 25-50 percent chance of SHRA/TSRA over the
mountains and deserts this afternoon, with the strongest storms
likely in the lower desert and desert foothills. Locally strong
surface gusts and reduced visibility in heavy rain and possibly
BLDU. CB bases near 8-10 kft MSL with tops 30-40 kft MSL.
Areas of west to southwest winds will gust to 25-40 knots this
afternoon and evening, strongest below the passes and on the high
desert slopes. MOD up/downdrafts likely over and NE/E of the
mountains.
&&
.MARINE...
Gusty south winds today and Saturday may produce rough conditions
near the entrance to the San Diego Bay. No hazardous marine
conditions expected Sunday through Tuesday.
&&
.BEACHES...
A series of long-period southerly swells, mostly in the 2-3 foot/15-
18 second range will gradually build today and Saturday, peak Sunday
and Monday, and gradually subside Tuesday and Wednesday. Surf of 3
to 5 feet with sets of 6 to 7 feet is expected in northern Orange
County. Elevated to locally high surf and a high risk of rip and
longshore currents will create hazardous swimming conditions at all
beaches through the holiday weekend.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch until 7 PM PDT this evening for Coachella Valley-San
Diego County Deserts-San Gorgonio Pass Near Banning.
PZ...None.
&&
PUBLIC...CO/17
AVIATION/MARINE/BEACHES...MMThe San Diego radar (KNKX), 117 km away, was scanning. The volume nearest the first event began at 20:01 UTC.
4 flash flood, 2 heavy rain, 2 dust storm, 1 flood. Local standard time, as filed.
Heavy rain fell across the Coachella Valley on September 1st, with totals of 0.50-1.50 common across the region. Some localized higher totals include 2.83 at Kent Sea FMS (KSFC1), 1.97 at an observation site 2 miles southeast of Thermal (WRPC1), and 1.22 at Morongo Valley (MSKC1).
Heavy rain fell across the San Bernardino County Mountains on September 1st, runoff from which contributed to some flooding near the Phelan area. Totals were largely in the 0.25-1.00 range, but some localized higher totals fell at Middle Fork Lytle Creek (MFLC1) where 1.56 of rain fell, with roughly 1.50 of rain falling in Wrightwood.
CalFire Riverside shared a video of several vehicles stranded in water 1 to 2 feet deep at 52nd Avenue and Education Way. One occupant was rescued.
Flooding occurred at 79650 Varner Road after 1.18 inches of rain fell nearby.
Dust storm captured on video near Anza Borrego Desert Park.
Flooding occurred at 67959 Lincoln Avenue after about 1.80 inches of rain fell nearby. Flooding continued through at least 10:30 AM on September 2nd, per CalTrans.
Visibility estimated as low as 100 feet locally along Interstate 10 north of Palm Springs.
Three people died in a car crash on Sunday afternoon in Palm Springs on North Gene Autry Trail. Police said the crash was caused by high winds that kicked up sand, severely reducing visibility. Winds at Palm Springs Airport ASOS at the time were NW 15-20 mph with gusts to 25-30 mph.
Crews at Empire Polo Field reported that 50th Avenue was flooded after 1.89 inches of rain fell in 4 hours.
Report of water flowing down Duncan Road and Sheep Creek Road, covering the westbound lanes in these areas.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Dust Storm, Coachella Valley | 2023-09-01 | Vehicle/Towed Trailer | Direct | ||
| Dust Storm, Coachella Valley | 2023-09-01 | Vehicle/Towed Trailer | Direct | ||
| Dust Storm, Coachella Valley | 2023-09-01 | Vehicle/Towed Trailer | Direct |
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, September 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: 1140337, 1140338, 1140327, 1140333, 1140340, 1140334, 1140339, 1140335, 1140336.