Flash Flooding and Debris Flow in California, January 15 to 17, 2019

Name: Flash Flooding and Debris Flow in California, January 15 to 17, 2019
Start: 2019-01-15T20:00
End: 2019-01-17T19:00
Location: California

January 15 to 17, 2019 · NWS SGX · 13 events in 6 counties and zones

Where it happened

Every event with a place to put it; 4 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: 35
Property damage: $55,000
Crop damage: $11,000
Events: 13

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 high impact mini atmospheric river impacted Southern California January 14th and 15th which brought heavy rain and snow to the region. Seal Beach reported 2 inches of rain in 2 hours, which caused extensive flash flooding. Water was up to doorways outside of homes, and the Pacific Coast Highway was closed for over a day in Huntington Beach due to flooding. Rainfall rates remained below flash flood thresholds at the Holy and Cranston burn scars during this mini-AR event. Dense fog was reported in the Cajon Pass on the morning of January 16th, which resulted in a 19-car pileup and 35 patients with minor to moderate injuries.

A larger atmospheric river moved into Southern California on January 17th, bringing heavy rain and snow to the region. Extensive flash flooding occurred due to the heavy rain. Swift water rescues occurred on the Santa Ana River in Riverside due to flooding. Rainfall rates exceeded flash flooding thresholds for the Holy fire burn scar on the 17th.

Overall, 6 to 12 inches of rain fell in the Santa Ana and San Bernardino County Mountains between January 14-17. Snowfall amounts in the mountains ranged from 4 to 12 inches above 6500 ft. Major surf and coastal flooding occurred during this event as well, which resulted in extensive damage of the Ocean Beach Pier in San Diego County.

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 15, 2:25 PM PST, 5 hours 35 minutes earlier.

Area forecast discussion, Jan 15, 2:25 PM PST, 5 hours 35 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
225 PM PST Tue Jan 15 2019

.SYNOPSIS...
A series of storms will bring periods of rain and mountain snow
through Thursday. Heavy rain is likely at times on the slopes of
the San Bernardino County mountains. Dry and warmer Friday through
Sunday with moderate offshore winds.

&&

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

Rain over the coastal waters this afternoon will race eastward and
overspread the area tonight. The rain extends from Santa Barbara
southward to the San Diego County coastal waters, which is a little
farther south than projected. The heaviest rain was over LA and
Ventura Counties at 2 PM and was moving east.

The rain is associated with a Pacific shortwave near Pt Conception
which is providing enough instability for thunderstorms over the
ocean. Moisture is plentiful with this first "mini" atmospheric
river (PW's of 0.90"), and the warm air advection will also
contribute to the rainfall totals. Highest amounts will be over the
south facing slopes of the San Bernardino Mountains where 1-3" are
likely, with highest amounts at the focal points for orographic
rains like Lytle Creek. Snow levels will remain fairly high in the
warm air advection, from 5,500-6,000 feet, with significant snow
accumulations above 8,000 feet.

On Thursday, a more impressive Atmospheric River will bring even
more substantial rain. The PW increases to around 1.25", which will
rank in the Top 20 of January PW's. The highest was 1.56" in January
of 1997. This system is also trending a little farther north with
greatest rain amounts in Orange, Riverside and San Bernardino
Counties, but San Diego County will see rain too. Rain amounts with
this third and final storm Thursday will range from 0.10"-0.50" in
the deserts and southern San Diego County to 2-5" on the south
facing slopes of San Bernardino County. Orange County coast and
inland areas and the Inland Empire, could receive 1-2" of rain. This
system may have the greatest risk of flash flooding and urban
flooding, and a Flash Flood Watch may be needed. Snow levels will
increase to 7500 ft Thursday, with large accumulations confined to
areas above 8000 ft, an only an inch or two between 6500-7500 ft.
Southwesterly wind gusts of 55-65 mph are possible Thursday as the
system moves across the region.

Upper-level ridging then builds in for the weekend, along with
surface high pressure over the Great Basin. This will help
generate gusty east to northeast winds across inland areas, and
increase high temperatures to above seasonal normals. Another
round of gusty offshore winds may develop next Tuesday.

&&

.AVIATION...
152130Z...Coasts/Valleys...SCT-BKN clouds with bases 1500-6000 ft
MSL will continue through this afternoon. Cigs lowering to blo 2000
ft MSL this evening through early Wednesday morning, with widespread
VIS 2-4SM in -RA developing by 03Z Wed.

Deserts...SCT-BKN with cloud bases 2500-5000 ft MSL. Cigs could
lower to blo 1500 ft at times through tonight.

Mountains...Obscured in clouds/fog/pcpn through tonight.

&&

.MARINE...
Showers, possibly with embedded thunderstorms are expected to move
eastward across the coastal waters this afternoon through tonight.
Winds increasing this afternoon and evening. A Small Craft Advisory
goes into effect 3PM PST today to 4AM PST Wednesday for wind gusts
up to 30 kt. Conditions improve on Wed before another storm arrives
Thursday evening into Friday, again generating rough seas.

&&

.BEACHES...
A west-northwest swell of 4-6 ft at 18 sec will gradually subside
through Wednesday. Another northwest swell arrives late Wednesday
and builds Thursday into Friday. Periods of high surf are likely
with this swell also. A Beach Hazards Statement continues through
Friday afternoon.

&&

.FIRE WEATHER...
Gusty east to northeast winds are expected at times for inland
areas this weekend and again next Tuesday. Afternoon relative
humidity will lower to near 20 percent away from the coast through
the period. Given the amount of wetting rains received across the
region this week, fire weather conditions are only expected to be
elevated, but not critical for the period.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 3 AM PST Wednesday for Riverside
     County Mountains-San Bernardino County Mountains.

     Beach Hazards Statement through Friday afternoon for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory for winds until 4 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...Moede
FIRE WEATHER...JJT
AVIATION/MARINE/BEACHES...PG

In the hours before

Local storm report, Jan 15, 7:08 PM PST, 52 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
708 PM PST TUE JAN 15 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0658 PM     HAIL             6 E MISSION VIEJO       33.64N 117.56W
01/15/2019  E0.25 INCH       ORANGE             CA   TRAINED SPOTTER

            ESTIMATED PEA SIZED HAIL REPORTED. SEVERAL
            CLOUD TO GROUND LIGHTNING STRIKES IN SANTA
            ANA MOUNTAINS IMMEDIATELY SOUTH OF TRABUCO
            CANYON (BELL CANYON AREA.).

&&

CO

The radar

The Santa Ana Mts radar (KSOX), 47 km away, was scanning. The volume nearest the first event began at 03:59 UTC.

Open the radar archive at this moment

Event by event

6 flash flood, 3 high wind, 2 heavy rain, 1 dense fog, 1 debris flow. Local standard time, as filed.

Flash Flood, Orange

When: January 15, 8:00 PM PST to 10:00 PM PST
Where: Orange County, 2.9 mi NW of Seal Beach to 2.97 mi S of Boulevard Gardens
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 33.757, -118.139

Heavy rainfall began 7 pm on January 15th and inundated downtown Seal Beach. The heavy rain also affected parts of Huntington Beach and Fountain Valley. The flooding in Seal Beach old town affected homes with water entering garages and first levels. The Pacific Coast Highway was closed through the 16th due to the flooding and standing water. Radar estimated 2 inches of rain in about 2 hours with totals over 3 inches across northwest Orange County.

Heavy Rain, Orange

When: January 15, 8:00 PM PST to 9:00 PM PST
Where: Orange County, 0.82 mi SW of Huntington Beach
Reported by: ASOS
Coordinates: 33.661, -118.009

Huntington Beach received 1.25 inches of rainfall in one hour between 2000 and 2100 PST on January 15th. Local officials closed the Pacific Coast Highway (route 1) at approximately 9pm January 15th and kept it closed through the afternoon hours of January 16th.

Heavy Rain, Orange

When: January 15, 8:00 PM PST to 10:00 PM PST
Where: Orange County, 0.79 mi NW of Fountain Vly
Reported by: ASOS
Coordinates: 33.708, -117.960

Fountain Valley received 2 inches of rain in 2 hours between 2000 and 2200 PST on January 15th. An industrial roof collapsed due to water build up at approximately 2200 PST on Mt. Hermann Street.

Dense Fog, San Bernardino County Mountains

When: January 16, 9:30 AM PST to 1:30 PM PST
Where: San Bernardino County Mountains forecast zone
Injuries: 0 direct, 35 indirect
Property damage: $25,000
Reported by: Broadcast Media
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Local media reported a 19 car pileup on southbound I-15 in the Cajon Pass due to dense fog in the morning hours of January 16th. 35 patients were treated for minor to moderate injuries.

Flash Flood, Riverside

When: January 16, 11:00 AM PST to 2:00 PM PST
Where: Riverside County, 0.55 mi NW of Glen Avon to 1.33 mi ENE of Mira Loma
Cause: Heavy Rain
Property damage: $10,000
Crop damage: $1,000
Reported by: Department of Highways
Coordinates: 34.026, -117.486

Highway 60 had lane closures due to heavy rain bands of 0.50 to 0.75 per hour. Multiple swift water rescues on the Santa Ana River including helicopter extractions along Fleetwood and Via Ricardo.

Flash Flood, Riverside

When: January 16, 1:00 PM PST to 3:00 PM PST
Where: Riverside County, 2.6 mi SSW of El Cerrito to 1.86 mi WSW of Alberhill
Cause: Heavy Rain / Burn Area
Property damage: $20,000
Crop damage: $10,000
Reported by: Fire Department/Rescue
Coordinates: 33.795, -117.537

Flash flooding from heavy rainfall over Holy fire scar in Trilogy parkway and Glen Eden with water going around homes.

Flash Flood, Riverside

When: January 17, 9:30 AM PST to 1:30 PM PST
Where: Riverside County, 1.84 mi SW of Arcilla to 1.72 mi SW of Arcilla
Cause: Heavy Rain / Burn Area
Reported by: Department of Highways
Coordinates: 33.762, -117.474

CalTrans reported Temescal Canyon Road at I-15 south closed due to flooding.

Debris Flow, San Bernardino

When: January 17, 10:30 AM PST to 1:30 PM PST
Where: San Bernardino County, 1.93 mi WNW of Running Spgs to 1.92 mi WNW of Running Spgs
Cause: Heavy Rain
Reported by: Department of Highways
Coordinates: 34.215, -117.128

CalTrans reported a mud/rock slide on Highway 18 at Live Oak Drive due to heavy rain.

Flash Flood, San Diego

When: January 17, 12:00 PM PST to 3:00 PM PST
Where: San Diego County, 4.33 mi ESE of Pala to 4.41 mi ESE of Pala
Cause: Heavy Rain
Reported by: Department of Highways
Coordinates: 33.341, -117.013

CalTrans reported highway 76 at Adams Drive flooded due to heavy rain.

Flash Flood, San Bernardino

When: January 17, 1:00 PM PST to 4:00 PM PST
Where: San Bernardino County, 1.69 mi N of Cedar Pines to 1.63 mi N of Cedar Pines
Cause: Heavy Rain
Reported by: Department of Highways
Coordinates: 34.274, -117.319

CalTrans reported 2 ft of water along Hwy 138 north of Cedarpines Park. A car stalled in the water, and 2 people had to be rescued.

High Wind, San Bernardino County Mountains

When: January 17, 5:30 PM PST to 6:30 PM PST
Where: San Bernardino County Mountains forecast zone
Measured: 53 kt (61 mph) measured gust
Reported by: Mesonet
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Snow Peak mesonet reported a peak wind gust of 54 knots between 1730 and 1830 PST on January 17th.

High Wind, San Bernardino County Mountains

When: January 17, 5:50 PM PST to 6:50 PM PST
Where: San Bernardino County Mountains forecast zone
Measured: 65 kt (75 mph) measured gust
Reported by: Mesonet
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Burns Canyon Mesonet reported a peak wind gust of 65 knots between 1750 and 1850 PST on January 17th.

High Wind, San Diego County Mountains

When: January 17, 6:00 PM PST to 7:00 PM PST
Where: San Diego County Mountains forecast zone
Measured: 55 kt (63 mph) measured gust
Reported by: Mesonet
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Harrison Park mesonet station reported a peak wind gust of 55 knots between 1800 and 1900 PST on January 17th.

What these are

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.
Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Dense Fog: Fog reducing visibility to a quarter mile or less, filed where it caused accidents or disruption.
Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.
High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.

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

The same day elsewhere

Every storm in California in 2019 Every state in 2019 This day in weather history Warnings in California, January 2019

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: 805116, 805122, 805123, 805124, 805119, 805121, 805127, 805128, 805129, 805130, 805131, 805125, 805126.