Monsoonal moisture moved into Southern California on August 15th and resulted in numerous showers and thunderstorms across the region. Heavy rain fell in the San Diego County Mountains on August 15th, and became more widespread on August 16th and 17th.
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 moisture moved into Southern California on August 15th and resulted in numerous showers and thunderstorms across the region. Heavy rain fell in the San Diego County Mountains on August 15th, and became more widespread on August 16th and 17th. Mount Laguna picked up 3.20 inches of rainfall on August 17th. Numerous areas of flash flooding and debris flows were reported throughout Southern California, particularly in the Riverside and San Bernardino County mountain areas. A landspout tornado was reported in the Anza Valley associated with a severe thunderstorm. No injuries or major damages were reported.
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 Aug 16, 12:28 PM PST, 1 hour 32 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
128 PM PDT Thu Aug 16 2018
.SYNOPSIS...
Scattered thunderstorms in the mountains and deserts will continue
into early evening. Monsoon moisture will decrease Friday and
Saturday, with fewer storms Friday mainly in the mountains. Dry
and warmer weather for the weekend. Coastal low clouds and fog
will continue nights and mornings. Monsoon moisture returns next
week for the next chance of thunderstorms most likely Tuesday
through Thursday.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Lots of thunderstorms have popped in the mountains and high desert
in Riverside and San Bernardino Counties. Some are very strong and
a few are probably producing flash floods and/or severe damaging
weather. These will taper off late afternoon and evening. The
flash flood watch is in effect through early evening, with
particular concern for the Cranston and Valley fire burn scars.
The monsoon moisture decreases during the day Friday for fewer
thunderstorms mainly in the mountains. Meanwhile, the marine layer
seems to continue undaunted and coastal clouds will continue to
reach into western valleys each night and morning. High pressure
builds aloft over California Friday and Saturday, which will
bring warmer inland weather this weekend. At the same time the
monsoon flow decreases, so no thunderstorms are expected. Model
solutions begin to diverge after five days as usual. Some guidance
suggests thunderstorms returning as early as Monday, but two out
of three extended models suggest waiting until Tuesday, and we're
going with that latter idea in our forecast. No big changes in the
temperature forecast next week. A generally shallow marine layer
and a small chance of thunderstorms each afternoon mainly in the
mountains.
&&
.AVIATION...
1620000Z...Coasts/Valleys...SCT/BKN stratus clouds lingering near
the immediate coast through this afternoon. Low clouds redeveloping
and spreading back inland after 17/03Z with slightly lower bases and
tops. Areas of BKN/OVC stratus 10-15 miles inland with bases mostly
1000-1500 ft MSL and tops to 2000-2500 ft MSL. Low clouds clearing
16Z-19Z Friday morning, except for a few BKN stratus decks lingering
along the immediate coast through Thursday afternoon. Otherwise FEW-
SCT clouds AOA 10 kft MSL.
Mountains/Deserts...Widespread SHRA/TSRA over the mountains and
deserts through early evening. With the TSRA, there will be strong
up/downdrafts, mtn obscurations, surface gusts to 40 knots, hail,
and LLWS. CB bases 8000 ft MSL and tops to 50000 ft MSL. Storms will
diminish by 03Z. Otherwise FEW-SCT clouds AOA 10 kft MSL.
&&
.MARINE...
No hazardous marine weather is expected through Monday.
&&
.BEACHES...
Beach Hazard Statement remains in effect through Friday for elevated
surf and strong rip currents. A Southern Hemisphere swell from 180
degrees, peaking at 4 ft/16-17 second period will bring surf of 3-6
ft and strong rip currents tonight through Friday. Isolated sets of
8 ft possible on south facing beaches Friday. Surf will begin to
lower Saturday.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flash Flood Watch until 8 PM PDT this evening for Apple and
Lucerne Valleys-Coachella Valley-Riverside County Mountains-
San Bernardino County Mountains-San Diego County Deserts-
San Diego County Mountains-San Gorgonio Pass Near Banning.
Beach Hazards Statement through Friday evening for Orange County
Coastal Areas-San Diego County Coastal Areas.
PZ...NONE.
&&
PUBLIC...MM
AVIATION/MARINE/BEACHES...BrothertonPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
208 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0116 PM DEBRIS FLOW 7 NE YUCAIPA 34.10N 116.96W
08/16/2018 SAN BERNARDINO CA PUBLIC
PUBLIC AND FIRE RADIO REPORTS THAT VALLEY OF
THE FALLS DR IS CLOSED DUE TO A DEBRIS FLOW.
&&
SNCPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
235 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0225 PM DEBRIS FLOW 3 E LUCERNE VALLEY 34.44N 116.90W
08/16/2018 SAN BERNARDINO CA LAW ENFORCEMENT
CHP REPORTS WATER AND MUD FLOODED ROADWAY ON
HWY 247 AND LOCUS AVE.
&&
SNCPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
241 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0150 PM TSTM WND GST APPLE VALLEY (6 N) 34.59N 117.17W
08/16/2018 M40 MPH SAN BERNARDINO CA MESONET
MESONET STATION GNTC1, APPLE VALLEY (6 N).
&&
AOTPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
251 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0235 PM FLASH FLOOD 1 SE CHERRY VALLEY 33.96N 116.95W
08/16/2018 RIVERSIDE CA LAW ENFORCEMENT
CHP REPORTS BROOKSIDE AVE AND HIGHLAND
SPRINGS AVE FLOODED OUT ON BOTH SIDES OF THE
ROAD.
&&
SNCPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
252 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0237 PM FLOOD 1 SE CHERRY VALLEY 33.96N 116.95W
08/16/2018 RIVERSIDE CA LAW ENFORCEMENT
CHP REPORTS ROAD FLOODED ON BOTH SIDES AT
INTERSECTION OF BROOKSIDE AVE /HIGHLAND
SPRINGS AVE IN BEAUMONT.
&&
BRPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
300 PM PDT THU AUG 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0255 PM HEAVY RAIN WRIGHTWOOD 34.36N 117.63W
08/16/2018 E1.00 INCH SAN BERNARDINO CA PUBLIC
TWO SPOTTERS REPORTED HEAVY RAIN IN
WRIGHTWOOD. ONE SPOTTER MENTIONED RAINFALL
RATES OF AT LEAST AN INCH AN HOUR. REPORTED
1/2 INCH SIZED HAIL, AS WELL AS THUNDER AND
LIGHTNING. MODERATE FLOODING REPORTED.
&&
SNCThe San Diego radar (KNKX), 79 km away, was scanning. The volume nearest the first event began at 21:58 UTC.
6 debris flow, 3 flash flood, 2 heavy rain, 1 tornado, 1 thunderstorm wind. Local standard time, as filed.
Public reports of a landspout tornado northwest of Anza, CA. No injuries or damages were reported.
Public and Fire Radio reported that Valley of the Falls Drive was closed due to a debris flow.
Apple Valley mesonet (gntc1) reported a 40 knot thunderstorm wind gust at approximately 2:50 PM PST on August 16th.
CHP reported that Brookside Avenue and Highland Springs Avenue was flooded out on both sides of the road from the heavy rain.
CHP reported that water and mud flooded the entire roadway on Highway 247 at Locus Ave. No damages or injuries reported.
CHP reported that Highway 18 near Johnston Road was flooded. A vehicle went off the road in that area into a pothole and became flooded with water. Persons in the vehicle made it out okay, but some damage to the vehicle from the water.
Two spotters reported heavy rainfall in Wrightwood -- approximately 1 inch per hour rainfall rate. Moderate flooding was reported.
A trained spotter reported 1.14 inches of rainfall in 35 minutes.
Public reported a debris flow at the Sheep Creek Wash in Wrightwood on Lone Pine Canyon Road. The road was closed down for a few hours to clean up the debris flow.
CHP reported a rock/dirt/mud slide along Highway 38 between Onyx Peak and the town of Sugarloaf. Law enforcement indicated that the road was covered in rocks. No injuries or damages reported.
California Department of Transportation reported that there were dozens of small debris flows in and around the Cranston Fire burn scar on August 15th but highway 74 was proactively closed based on NWS warnings. On August 17th, there was a large debris flow up to 5 feet deep in the Lake Hemet Campground area from Hurkey Creek. Again highway 74 was closed about 2 hours in advanced based on NWS briefings and the actual Flash Flood Warning. Very large boulders were reported to have traveled downstream on the upper Hurkey Creek near Fleming Ranch. Evacuations were in order at Hurkey Creek Campground and Sheriff was on site monitoring the potential based on NWS briefings. Video of the debris flow was captured. A storm survey was conducted by NWS following the debris flow. No injuries or major damages reported from this event. Rain gauges in the area reported 1-1.5 inches of rainfall near the Cranston Fire burn scar. Evacuations of the small communities near the Cranston Fire burn scar were put into place on August 15th in anticipation of the heavy rainfall and potential for flash flooding and debris flows.
CHP reported boulders across the roadway on Highway 74 in Pinyon Pines near the fire station. No injuries or damages were reported.
Sheriff reported that a major debris flow occurred on Highway 74 near the Cranston Fire burn scar. No injuries or damages were reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyThe tornado archive for California, 2018Warnings in California, August 2018
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: 782665, 782677, 782687, 782676, 782678, 782683, 782690, 782692, 782693, 782699, 782656, 782697, 782696.