Flash Flood and Flood in California, September 28 to 29, 2022

Name: Flash Flood and Flood in California, September 28 to 29, 2022
Start: 2022-09-28T14:00
End: 2022-09-29T14:00
Location: California

September 28 to 29, 2022 · NWS SGX · 6 events in 3 counties and zones

Monsoon thunderstorms occurred on September 28 and 29, mainly impacting the mountains of San Bernardino, Riverside and San Diego Counties. Several reports of local flash flooding, heavy rain and small hail were received.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 6

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.

What happened

The episode as NWS SGX wrote it up.

What forecasters said that day

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 28, 1:20 PM PST, 40 minutes earlier.

Area forecast discussion, Sep 28, 1:20 PM PST, 40 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
Issued by National Weather Service Los Angeles/Oxnard CA
220 PM PDT Wed Sep 28 2022

.SYNOPSIS...
The weather will turn gradually cooler through Saturday
as high pressure over the Southwest weakens. A shallow marine layer
will bring areas of dense fog to the coastal areas tonight and
Thursday morning. Low clouds and fog will spread into the western
valleys Friday and Saturday as the marine layer deepens.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.SHORT TERM...

Thunderstorms over the mountains and deserts this afternoon will
dissipate this evening. The SPC mesoanalysis showed the precipitable
water jumped to 1.3” over the lower deserts today, fueling
convection with the heat of the day. CAPE values ranged from 500-
1000J/kg over the deserts. Moisture and CAPE decreases tonight and
Thursday with increasingly drier air moving in from the northwest.
Any thunderstorm activity over the mountains tomorrow will be more
isolated.

West of the mountains the return of a shallow marine layer brought
dense fog to the coastal zones, the beaches and the inner coastal
waters. Clouds and fog clung to a some of the Orange County and San
Diego County beaches this afternoon. The marine layer depth won’t
change much tonight so dense fog is likely again Thursday morning.

The marine layer will deepen Thursday night and Friday when a
Catalina Eddy spins up over the coastal waters, sending low clouds
and fog into inland Orange County and the western San Diego County
Valleys Friday and Saturday mornings where dense fog will be most
likely.

The overall trend Friday through Sunday is for cooler weather to
move in from west to east as a 500 mb trough moves across the
Pacific Northwest and northern California. This will bring a drier,
cooler airmass and stronger onshore flow through the weekend.

&&

.AVIATION...
.282045Z…Coast/Valleys…Some low clouds will linger near/just
offshore through this afternoon. Areas of low clouds/fog will
develop again this evening over the coasts and valleys. CIGS likely
after 03z Thu, bases 300-700 FT MSL and tops to near 900 FT MSL. VIS
0-4SM in BR/FG in portions of the coastal valleys and coastal mesas.
Low clouds/fog scatter out between 16-18z Thu.

Mtns/Deserts…Cumulus and CB based near 10000 FT MSL with SCT TSRA
developing in the mountains through 03z Thu, tops near 30-40K FT
MSL.  Gusty and erratic winds as well as heavy downpours expected
near any TSRA. Mostly clear skies then expected after 03z.

&&

.MARINE...
No hazardous marine conditions are expected through Sunday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT this evening for Orange
     County Coastal Areas-San Diego County Coastal Areas-San Diego
     County Valleys-Santa Ana Mountains and Foothills.

     Excessive Heat Warning until 8 PM PDT this evening for Coachella
     Valley-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Deserts-San Gorgonio Pass Near Banning.

PZ...None.

&&

PUBLIC...Moede
AVIATION/MARINE...Adams

The radar

The Santa Ana Mts radar (KSOX), 88 km away, was scanning. The volume nearest the first event began at 22:00 UTC.

Open the radar archive at this moment

Event by event

3 heavy rain, 1 flash flood, 1 flood, 1 hail. Local standard time, as filed.

Heavy Rain, Riverside

When: September 28, 2:00 PM PST to 3:01 PM PST
Where: Riverside County, 5.03 mi NNE of Idyllwild
Reported by: Mesonet
Coordinates: 33.815, -116.680

Mesonet station VGRC1 Vista Grande reported 0.75 inch of rain in one hour.

Heavy Rain, San Bernardino

When: September 28, 2:00 PM PST to 4:00 PM PST
Where: San Bernardino County, 2 mi SE of Yucaipa to 3 mi ESE of Yucaipa
Reported by: Mesonet
Coordinates: 34.010, -117.005

Thunderstorms produced moderate rainfall southeast of Yucaipa. A trained spotter reported 0.56 inch of heavy rain, and Mesonet station CW1772 Yucaipa reported 1.06 inch of rain in one hour.

Flash Flood, San Bernardino

When: September 28, 3:00 PM PST to 5:00 PM PST
Where: San Bernardino County, 0.77 mi SE of Dunlap Acres to 1.6 mi ESE of Dunlap Acres
Cause: Heavy Rain
Reported by: Public
Coordinates: 34.012, -117.111

Law enforcement reported roadway flooding on I-10 along the Riverside/San Bernardino County line. County and Bryant Road intersection closed due to flooding, with several inches of water over the roadway. Social media reports of flood damage to inside of garages and backside of two homes in the area. CWOP site in Yucaipa reported 0.84 inch of rain in 25 minutes.

Flood, Riverside

When: September 28, 4:00 PM PST
Where: Riverside County, Idyllwild to 1.26 mi WNW of Saunders
Cause: Heavy Rain
Reported by: NWS Employee
Coordinates: 33.750, -116.720

Flooding reported along Highway 243 in Pine Cove near Idyllwild, with small gravel and mud flows noted. Small hail (0.25 inch in diameter) was also reported.

Heavy Rain, Riverside

When: September 29, 1:00 PM PST to 2:00 PM PST
Where: Riverside County, 12 mi SW of La Quinta
Reported by: Mesonet
Coordinates: 33.547, -116.448

Mesonet station on Toro Peak via HPWREN reported 0.52 inch of rain in one hour.

Hail, San Diego

When: September 29, 1:09 PM PST to 1:20 PM PST
Where: San Diego County, 63.85 mi ESE of San Juan Hot Spgs
Measured: 0.75 in hail
Reported by: Trained Spotter
Coordinates: 33.213, -116.484

Trained spotter reported penny size (0.75 inch) hail associated with a heavy thunderstorm.

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in California in 2022 Every state in 2022 This day in weather history Warnings in California, September 2022

Sources

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: 1057429, 1057431, 1057433, 1057432, 1057439, 1057438.