Flash Flood and Debris Flow in California, January 8 to 9, 2018

Name: Flash Flood and Debris Flow in California, January 8 to 9, 2018
Start: 2018-01-08T10:00
End: 2018-01-09T20:00
Location: California

January 8 to 9, 2018 · NWS SGX · 12 events in 8 counties and zones

Where it happened

Every event with a place to put it; 5 filed by county or forecast zone are drawn at its center, in a lighter ring. 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

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $129,000
Crop damage: None recorded
Events: 12

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.

A moderate strength trough of low pressure swept through the SoCal Bight with gusty winds, mountain snow and heavy rainfall. Rainfall totals of 1-2 inches occurred over the coast and valleys, with isolated amounts of 6-8 inches along favored coastal slopes. Snowfall was 2 to 8 inches above 6,000 ft with up to 12 inches on the higher peaks. Wind caused major damage to the historic Bay Theater in San Diego. Around 10 swift water rescues were reported in the Inland Empire and San Bernardino County Mountains.

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 Jan 8, 9:30 AM PST, 30 minutes earlier.

Area forecast discussion, Jan 8, 9:30 AM PST, 30 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PST Mon Jan 8 2018

.SYNOPSIS...
Light rain and showers are likely today into this evening ahead
of a Pacific storm that will bring more widespread and heavier
precipitation and strong gusty winds late tonight into Tuesday
evening. Wind and showers will decrease Late Tuesday night into
Wednesday morning. Warmer and dry for Thursday through next
weekend with locally gusty northeast winds near the coastal
foothills at times.

&&

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

Mostly cloudy this morning ahead of an approaching storm, with
light rain and showers over the region north of San Diego County.
So far, only a few hundredths of an inch of rain have fallen in
northern Orange County and the mtns of San Bernardino and
Riverside counties. The rain and showers will spread south and
east through today, remaining mostly light with some breaks this
afternoon. Winds will remain light through this afternoon,
increasing from the south this evening through early Tue morning.

Through Wednesday... The storm will move inland across Southern
California Tuesday, and into Arizona Tuesday night. This storm is
fairly typical of a mid-latitude cyclone, with a well-defined
frontal boundary.

The most widespread and heaviest precipitation is expected with
the passage of the cold front early Tuesday morning, and periods
of locally intense rainfall will be possible. Periods of showers
will follow into Tuesday evening, decreasing from the northwest late
Tuesday night into Wednesday morning. There is also a slight
chance of thunderstorms with the cold front early Tuesday morning,
and again Tuesday afternoon into Tuesday evening as the coldest
air aloft moves across far southern California, destabilizing the
atmosphere.

South to southeast winds will strengthen for late tonight into
early Tuesday morning ahead for the cold front with isolated gusts
to near 50 mph possible towards the coast. Winds will shift to the
southwest to west behind the cold front for later Tuesday morning
into Tuesday evening. Convective wind gusts accompanying the cold
frontal passage could be strong enough to produce minor damage.

Fair weather returns on Wednesday, with the beginning of a warming
trend.

Thursday through Sunday... High pressure rebuilds over the West
Coast to bring dry and warmer weather. Surface high pressure over
the Great Basin may bring some mostly weak gusty northeast winds
near the coastal foothills at times.

&&

.AVIATION...
081730Z...Widespread clouds with bases 7000-10000 ft MSL will
prevail today with scattered very light showers. Local vis will be 3-
5 miles through 19Z in BR/-SHRA. The clouds will gradually lower
overnight with rain increasing, and by 12Z Tue most areas will have
bases 900-2500 ft MSL and areas of vis 2-4 miles in RA. There is a
chance of thunderstorms Tuesday with strong up/downdrafts. Areas of
winds from the south 15-30 knots with gusts to 40 knots will occur
near the coast mainly 09Z-17Z Tue and areas of 20-35 knots with
gusts to 55 knots in the mountains and deserts. Winds will become
westerly in most areas after 17Z Tue.

&&

.MARINE...
The Pacific storm system will increase winds and waves late tonight
through Tuesday, with gale force winds possible, primarily just
ahead of the cold front. Wind gusts over 35 knots could occur in the
southerly flow mainly between 2 AM and 8 AM Tuesday before the wind
becomes westerly though with slightly lower wind speeds. Combined
waves will increase, with sloppy seas late tonight and Tuesday 8-10
feet, with possible 12 foot seas from a 12-second swell Tuesday
night, with gradual decreases Wednesday. Plans are to convert the
Gale Watch to a Gale Warning in the afternoon forecast.

&&

.BEACHES...
Surf will increase due to a couple of westerly swells associated
with the storm system Tuesday, with surf likely peaking very early
Wednesday. Surf will be highest in northern Orange County and
southern San Diego County where 3-6 foot choppy surf Tuesday will
build to 4-7 feet Wednesday morning with a few higher sets, then
gradually diminish. A Beach Hazard Statement will likely be needed
Tuesday and Wednesday. There is also a threat of lightning Tuesday.

&&

.HYDROLOGY...
A Pacific storm will bring periods of rain and showers to Southern
California today through Tuesday. The most widespread and
heaviest rainfall is expected with the passage of the cold front
early Tuesday morning. Rainfall rates of one-half to one inch per
hour for a 15-30 minute period with the front.

For Orange and San Bernardino Counties...rainfall will range from
1 to 1.5 inch near the coast, 2 to 4 inches in the mountains with
isolated amounts to 6 inches on the coastal slopes of the San
Bernardino County mountains. For San Diego and Riverside
Counties, amounts will range from 0.75 to 1.25 inch near the
coast, to 1.5 to 2.5 inches in the mountains with isolated
greater amounts. In the upper deserts, around one half inch is
expected, except around one inch near the desert foothills of the
San Bernardino County mountains. Amounts in the lower deserts
will mostly be one quarter inch or less with isolated amounts to
one half inch.

Rainfall rates with the front...and with showers and isolated
thunderstorms following the front Tuesday afternoon and evening
will be sufficient to cause mud and debris flows near recent burn
areas in Orange...Riverside...and San Bernardino Counties. Less
impact is expected for the Lilac burn area due to modest terrain
influence...and in the older burn areas in San Diego County. The
threat of mud and debris flows exists in areas of steep terrain
away from recent burn scars, however this threat is much lower.

The San Diego River through Fashion Valley is expected to remain
below flood stage...but could be near monitor levels late Tuesday
night to be near the lowest water crossings.

Snow levels above 8000 feet today will fall below 7000 feet
Tuesday morning then to around 5500 to 6000 feet Tuesday
afternoon and around 5000 feet Tuesday evening. Snowfall of 4 to
8 inches above 5000 feet is probable in San Bernardino and
Riverside Counties, with isolated amounts exceeding 18 inches
above 8000 feet.

&&

.SKYWARN...
Skywarn activation may be needed at times for late tonight through
Tuesday evening.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from 6 AM to 10 PM PST Tuesday for Coachella
     Valley-San Diego County Deserts-San Diego County Mountains-
     San Gorgonio Pass Near Banning.

     High Wind Warning from midnight tonight to 10 PM PST Tuesday for
     Apple and Lucerne Valleys.

     Winter Storm Warning from midnight tonight to 10 PM PST Tuesday
     for Riverside County Mountains-San Bernardino County
     Mountains.

     Wind Advisory from midnight tonight to 6 PM PST Tuesday for
     Orange County Coastal Areas-Orange County Inland Areas-San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Coastal Areas-San Diego County Valleys-
     Santa Ana Mountains and Foothills.

     Flash Flood Watch from late tonight through Tuesday evening for
     Orange County Inland Areas-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Gorgonio Pass Near
     Banning-Santa Ana Mountains and Foothills.

PZ...Gale Watch from late tonight through Tuesday morning for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm-Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

     Small Craft Advisory from 10 PM this evening to 1 AM PST Tuesday
     for Coastal Waters from San Mateo Point to the Mexican
     Border and out to 30 nm-Waters from San Mateo point to the
     Mexican Border Extending 30 to 60 nm out including San
     Clemente Island.

     Small Craft Advisory from 9 AM Tuesday to 1 AM PST Wednesday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm-Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente
     Island.

&&

PUBLIC/HYDROLOGY...PG
AVIATION/MARINE/BEACHES...Maxwell

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

5 flood, 3 strong wind, 1 winter weather, 1 high wind, 1 debris flow, 1 flash flood. Local standard time, as filed.

Winter Weather, San Bernardino County Mountains

When: January 8, 10:00 AM PST to January 9, 8:00 PM PST
Where: San Bernardino County Mountains forecast zone
Reported by: Department of Highways
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Several rounds of snow impacted the area over roughly a 36 hour period. Peak snowfall amounts of 12 inches were reported above 7000 ft (12 inches at Green Valley Lake). Between 5,500 ft and 7,000 ft amounts were in the 2-8 inch range. Big Bear Lake and Wrightwood reported 2 inches, with 8 inches in Running Springs.

Strong Wind, San Diego County Coastal Areas

When: January 9, 5:00 AM PST to 7:00 AM PST
Where: San Diego County Coastal Areas forecast zone
Measured: 49 kt (56 mph) measured gust
Property damage: $75,000
Reported by: Broadcast Media
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Multiple mesonets reported peak wind gusts in the 50-57 mph range between 0500 and 0700 PST, with the focus on southern San Diego. The historic Bay Theater lost it's sign and part of the front of the theater in National City.

Strong Wind, San Diego County Valleys

When: January 9, 5:00 AM PST to 8:00 AM PST
Where: San Diego County Valleys forecast zone
Measured: 49 kt (56 mph) estimated gust
Property damage: $10,000
Reported by: Mesonet
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

A 56 mph wind gust was reported at Otay Mountain. Around 6 large trees were reported down between San Marcos and Fallbrook. Peak winds gusts were in the 50-57 mph range.

Flood, Riverside

When: January 9, 6:00 AM PST to 7:00 AM PST
Where: Riverside County, 0.45 mi WNW of Menifee to 0.46 mi NNW of Menifee
Cause: Heavy Rain
Property damage: $25,000
Reported by: Law Enforcement
Coordinates: 33.733, -117.157

Several vehicles were stuck in mud and flooded out. Additional urban flooding was reported elsewhere in the Inland Empire.

High Wind, San Diego County Mountains

When: January 9, 6:00 AM PST to 7:00 AM PST
Where: San Diego County Mountains forecast zone
Measured: 62 kt (71 mph) measured gust
Reported by: Mesonet
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

A wind gust of 71 mph was reported a Palomar Lookout, with several other gusts into the 60s near Palomar Mountain. Peak wind gusts in the rest of the area were largely in the 35-50 mph range. No was damage reported.

Strong Wind, San Bernardino and Riverside County Valleys - the Inland Empire

When: January 9, 6:00 AM PST to 8:00 AM PST
Where: San Bernardino and Riverside County Valleys - the Inland Empire forecast zone
Measured: 43 kt (49 mph) estimated gust
Property damage: $1,000
Reported by: Law Enforcement
Coordinates: 34.293, -116.086 (the zone’s center; the record gives no point)

CHP reported two large trees down along Sage Road.

Debris Flow, Riverside

When: January 9, 6:00 AM PST to 9:00 AM PST
Where: Riverside County, 0.19 mi W of Prado Dam to 0.59 mi WSW of Corona
Cause: Heavy Rain
Property damage: $1,000
Reported by: Social Media
Coordinates: 33.880, -117.653

A minor debris flow was reported along Green River Rd. in Corona. The flow was associated with the Canyon 1 Fire.

Flood, San Bernardino

When: January 9, 7:00 AM PST to 9:00 AM PST
Where: San Bernardino County, 1.79 mi W of Grand Terrace to 1.18 mi W of Colton
Cause: Heavy Rain
Reported by: Fire Department/Rescue
Coordinates: 34.017, -117.381

Three people and a dog were rescued by helicopter from the Santa Ana River Channel at Agua Mansa Rd. and Riverside Ave. in Colton. Several other individuals were swept down stream and rescued in Riverside.

Flood, Orange

When: January 9, 7:00 AM PST to 8:00 AM PST
Where: Orange County, 55.71 mi SE of San Clemente to 57.13 mi SE of San Clemente
Cause: Heavy Rain
Property damage: $5,000
Reported by: Law Enforcement
Coordinates: 32.850, -116.939

CHP reported large chunks of wood floating down Lemon Crest Dr., the intersection of Lake Jennings Park Rd. and Pino Dr. was completely flooded.

Flood, San Bernardino

When: January 9, 7:00 AM PST to 9:00 AM PST
Where: San Bernardino County, 1.45 mi ESE of Summit to 1.46 mi NW of Cedarpines Park
Cause: Heavy Rain
Property damage: $1,000
Reported by: Department of Highways
Coordinates: 34.326, -117.395

CalTrans reported mud and debris flowing onto Hwy 138, resulting in a closure of the highway.

Flood, San Bernardino

When: January 9, 7:00 AM PST to 9:00 AM PST
Where: San Bernardino County, 1.58 mi SW of Cedar Glen to 1.4 mi SSE of Cedar Glen
Cause: Heavy Rain
Property damage: $1,000
Reported by: Department of Highways
Coordinates: 34.183, -117.188

Rains resulted is several rock falls along Hwy 330, that lead in a temporary road closure.

Flash Flood, San Bernardino

When: January 9, 8:45 AM PST to 9:30 AM PST
Where: San Bernardino County, 0.92 mi SW of Scotland to 2.83 mi SSW of Scotland
Cause: Heavy Rain
Property damage: $10,000
Reported by: Fire Department/Rescue
Coordinates: 34.241, -117.511

A van drove into flood waters flowing through the normally dry Lytle Creek, resulting in a swift water rescue.

What these are

Winter Weather: Snow, sleet or freezing rain below warning levels that still caused disruption, damage or casualties.
Strong Wind: Non-thunderstorm winds below high wind criteria that nonetheless caused damage or casualties.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.
Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.
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.

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

The same day elsewhere

Every storm in California in 2018 Every state in 2018 This day in weather history Warnings in California, January 2018

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: 737478, 737471, 737475, 737462, 737472, 737474, 737589, 737461, 737464, 737560, 737563, 737460.