Flash Flooding and Debris Flow in California, February 17 to 19, 2017

Name: Flash Flooding and Debris Flow in California, February 17 to 19, 2017
Start: 2017-02-17T07:30
End: 2017-02-19T16:00
Location: California

February 17 to 19, 2017 · NWS SGX · 18 events in 9 counties and zones

Where it happened

Every event with a place to put it; 10 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: 2
Injuries: 2
Property damage: $13 million
Crop damage: $100,000
Events: 18

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 strong trough and associated Pacific cold front swept into Southern California from the west, bringing strong winds, heavy snow and rain. The storm was noteworthy for the strong prefrontal southerly winds that produced significant tree damage over the coast and valleys. In the mountains the ski resorts received 1-2 ft of snow, while elevations as low as 5,000 ft saw a few inches of accumulation. Rainfall ranged from 2-6 inches along the coastal slopes to 1-2 inches at the coast. At the beaches surf heights reached 8 to 12 ft. Damages, primarily from wind, reached into the millions of dollars.

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 Feb 17, 3:59 AM PST, 3 hours 31 minutes earlier.

Area forecast discussion, Feb 17, 3:59 AM PST, 3 hours 31 minutes before

Area Forecast Discussion
National Weather Service San Diego CA
359 AM PST Fri Feb 17 2017

...Major Pacific storm system to bring significant weather-
related impacts to the region...including damaging wind gusts and
flooding...later today through tonight...

.SYNOPSIS...
Significant impacts later today through tonight as a strong
Pacific storm moves across the region through Saturday. This
storm will bring damaging winds and heavy precipitation to the
area. The most significant impacts are expected to occur this
afternoon through late tonight. Scattered to numerous showers will
continue Saturday and Saturday night...with additional snow
accumulation possible in the mountains. Dry weather returns
Sunday, but some lighter rain is possible Monday and again
Wednesday.

&&

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

The forecast hasn't changed much this morning. Major impacts are
likely with this storm system...possibly the strongest storm we've
seen over the past season.

Water vapor satellite loop early this morning depicts a vigorous
shortwave trough off the California coast about 700 nm west of
Monterey Bay. This system is quickly digging and deepening and
negatively tilting...and will form into a compact closed low this
morning off the CA coast. A deep plume of tropical moisture is
being drawn into this system from the Western Pacific...and
satellite estimates of precipitable water are now nearly 2 inches
which is about 3 x's climatology.

While light rain is moving through Southern California early this
morning well out ahead of this system...the brunt of the storm
will not arrive until this afternoon from the West...spreading SE
this evening with periods of very heavy rainfall. Heaviest
rainfall amounts will be over northern areas with a little lower
amounts over SD County. With very high atmospheric moisture in
place rainfall rates of one-half to up to 1 inch per hour will be
possible during the height of the rain event with highest rates along
favorable SSW facing slopes. This amount of short-duration
rainfall will likely lead to significant flooding issues in
urbanized areas and flash flooding in the mountains.

...Rainfall forecast through tonight...

ORANGE COUNTY..............2.5 to 5 inches (highest totals in the
                           Santa Ana Mountains).
SAN BERNARDINO MOUNTAINS...3 TO 8 inches (highest along SSW slopes).
RIVERSIDE COUNTY...........2 TO 3 inches.
SAN DIEGO COUNTY...........1.5 TO 2.5 inches.
UPPER AND LOWER DESERTS....0.5 to 1 inch.

Snow levels will be quite high during the heaviest precipitation,
around 7000 feet, and then lowering to about 5500 feet by Saturday
morning, with continued snow shower activity likely on Saturday
and Saturday night over the mountains where several inches of
additional snow will be likely. Total Snowfall forecast is for 6
to 12 inches between 6000 to 7000 feet, 1 to 2 feet between 7000
to 8000 feet, with isolated amounts of 2 to 3 feet possible above
8000 feet. A few inches of snow could fall as low as 5500 feet on
Saturday and Saturday night...bringing winter impacts to the
mountain passes.

The period of very strong winds is most likely to occur between
noon and 10 pm. Gusts of 50 to 70 mph along the coast and into
the valleys and deserts will certainly be capable of significant
downed trees and the potential for power outages and property
damage. In the mountains and along the desert slopes, gusts could
be as high as 80 to 90 mph during this time. We urge people to be
extremely cautious around any downed powerlines as electrocution
is a possibility if in contact with these live wires or ground
cover nearby.

As quickly as this system will have blown into SoCal, it will
depart by early Saturday morning, with winds greatly diminishing
and scattered rain and mountain snow showers in the mountains
through Saturday night, in a robust WNW flow regime.

Transitory ridging building into SoCal early next week will bring
an end to the showers and a moderating period. A mid week system
is now looking more like an inside slider and may not bring much
precipitation this far south, so just a chance of rain in the
forecast for Wednesday-Wednesday night.

&&

.AVIATION...
171030Z...SCT-BKN low clouds with bases 1500-2000 ft MSL and BKN-OVC
layers AOA 10000 ft MSL becoming multiple thick BKN-OVC layers
between 1000 and 25000 ft MSL by late morning. A strong storm will
bring widespread +RA and very strong south winds across most areas
by the early afternoon. CIGS lowering to 500 ft MSL with VIS 2SM or
less in +RA/BR. -SHRA continuing overnight with some improvement in
CIGS/VIS. Coastal slopes of the mtns will be obscured in
clouds/precip this afternoon through at least Saturday morning.

Southerly wind gusts of 30-50 kt are expected across the coast,
valleys and deserts. 60-70 kt gusts possible over portions of the
mountains. STG-SVR uddfs/llws is possible over and N, NE and E of
the mountains Friday. Winds will weaken substantially tonight as the
front passes.

&&

.MARINE...
A strong storm will generate near storm-force south winds late this
morning through tonight , with strongest winds potentially touching
50 kt this evening. A couple of large west swells will occur as
well, peaking at 17 feet/14 sec/270 degrees on Saturday. Large
combined seas will create hazardous seas through Sunday. A Gale
Warning remains in effect this afternoon through Sunday. Periods of
rain are expected at times today through Sunday, with the heaviest
rain this afternoon and evening. Isolated thunderstorms are possible
late this evening through Saturday.

&&

.BEACHES...
A large, long-period west-northwest swell from 280 degrees will
create surf of 5-9 ft today. Swell and surf will build further
tonight, peak Saturday at 17 ft/15 seconds/280 deg, then lower
gradually on Sunday. This will result in very large and potentially
damaging sets of 15 ft by late Saturday. Some low-lying coastal
areas could be at risk of minor coastal flooding due to large surf
and rainfall runoff. Powerful rip currents will accompany the high
surf as well. A High Surf Warning remains in effect through Sunday
evening. Surf will gradually lower during the day Sunday.

There is also a slight chance for thunderstorms at the beaches late
this evening through Saturday.

&&

.SKYWARN...
Skywarn activation is requested...for this afternoon through
tonight...for damaging winds, heavy rain and flooding, and heavy
snow in the mountains. All spotter volunteers are requested to
send in reports of severe weather via normal channels. Thanks!

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from 7 AM this morning to 2 AM PST Saturday
     for Apple and Lucerne Valleys-Coachella Valley-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 Deserts-San
     Diego County Mountains-San Diego County Valleys-San
     Gorgonio Pass Near Banning-Santa Ana Mountains and
     Foothills.

     Flash Flood Watch from noon PST today through Saturday afternoon
     for Apple and Lucerne Valleys-Coachella Valley-Orange
     County Coastal Areas-Orange County Inland Areas-Riverside
     County Mountains-San Bernardino County Mountains-San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Coastal Areas-San Diego County Deserts-San
     Diego County Mountains-San Diego County Valleys-San
     Gorgonio Pass Near Banning-Santa Ana Mountains and
     Foothills.

     Winter Storm Warning from 7 AM this morning to 7 AM PST Saturday
     for Riverside County Mountains-San Bernardino County
     Mountains.

     High Surf Warning until 10 PM PST Sunday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...Gale Warning from 7 AM this morning to 10 PM PST Sunday 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...Brotherton
AVIATION/MARINE/BEACHES...SS

The radar

The Edwards AFB radar (KEYX), 129 km away, was scanning. The volume nearest the first event began at 00:01 UTC.

Open the radar archive at this moment

Event by event

6 high wind, 5 flash flood, 2 high surf, 1 strong wind, 1 heavy snow, 1 debris flow, 1 thunderstorm wind, 1 flood. Local standard time, as filed.

High Wind, San Bernardino County Mountains

When: February 17, 7:30 AM PST to 6:00 PM PST
Where: San Bernardino County Mountains forecast zone
Measured: 73 kt (84 mph) measured gust
Reported by: Mesonet
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

The Burns Canyon mesonet reported frequent 70 to 80 mph gusts over a 9 hour period, with a peak gust of 84 mph between 1151 and 1251PST. A gust to 71 mph also occurred at Heaps Peak near Running Springs between 1015 and 1115PST. No damage reports were received.

High Wind, San Diego County Coastal Areas

When: February 17, 10:00 AM PST to 7:00 PM PST
Where: San Diego County Coastal Areas forecast zone
Measured: 53 kt (61 mph) measured gust
Deaths: 1 direct, 0 indirect
Property damage: $7.0 million
Crop damage: $100,000
Reported by: County Official
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Strong southerly winds downed hundreds of trees across coastal San Diego County. Many Cars were crushed by falling trees, power lines were downed, homes and business were damaged and one fatality was reported in East San Diego. The San Diego metro was hardest hit, with several mesonet/ASOS sites reporting wind gusts in the 50 to 60 mph range. A peak gust of 61 mph occurred at Imperial Beach. Storm damages reached the millions of dollars.

High Wind, Apple and Lucerne Valleys

When: February 17, 10:00 AM PST to 7:00 PM PST
Where: Apple and Lucerne Valleys forecast zone
Measured: 63 kt (72 mph) measured gust
Property damage: $50,000
Reported by: Mesonet
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Frequent wind gusts in the 55-65 mph range were measured by mesonet stations in Hesperia, with a peak gust of 72 mph between 1410 and 1420PST. Big rigs were blown over along Interstate 15 below the Cajon Pass and along Phelan Rd. west of Hesperia.

High Wind, San Diego County Valleys

When: February 17, 11:00 AM PST to 8:00 PM PST
Where: San Diego County Valleys forecast zone
Measured: 50 kt (58 mph) measured gust
Property damage: $2.0 million
Reported by: Law Enforcement
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Numerous trees were downed across the western valleys of San Diego County. Peak wind gusts generally ranged between 35 and 50 mph, though a peak gust of 58 mph was reported at Otay Mountain between 1414 and 1514PST.

High Surf, San Diego County Coastal Areas

When: February 17, 1:00 PM PST to February 18, 9:00 PM PST
Where: San Diego County Coastal Areas forecast zone
Reported by: Lifeguard
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Multiple lifeguard reports of high surf along the San Diego County coast. Oceanside Beach reported 8-12 ft surf with peak sets near 16 ft on the afternoon of the 18th. Imperial Beach reported sets to 8 ft. Average sets of 7 ft were reported at Mission Beach and Solana Beach.

High Wind, Orange County Coastal

When: February 17, 1:00 PM PST to 7:00 PM PST
Where: Orange County Coastal forecast zone
Measured: 52 kt (60 mph) measured gust
Property damage: $75,000
Reported by: Mesonet
Coordinates: 33.677, -117.776 (the zone’s center; the record gives no point)

Mesonet stations along the coast reported wind gusts in the 30 to 45 mph range over a 6 hour period between 1300 and 1900PST. An isolated peak gust of 60 mph occurred at San Clemente Pier. Numerous trees were downed over the coastal areas.

Strong Wind, Orange County Inland

When: February 17, 1:00 PM PST to 7:00 PM PST
Where: Orange County Inland forecast zone
Measured: 39 kt (45 mph) estimated gust
Property damage: $200,000
Reported by: Mesonet
Coordinates: 33.677, -117.776 (the zone’s center; the record gives no point)

Mesonet stations across inland Orange County reported wind gusts of 30 to 45 mph over a 6 hour period between 1300 and 1900PST. Numerous trees and a few power lines were downed in Santa Ana and Tustin. The falling trees smashed cars blocked roadways.

High Wind, San Diego County Mountains

When: February 17, 2:00 PM PST to 8:00 PM PST
Where: San Diego County Mountains forecast zone
Measured: 65 kt (75 mph) measured gust
Reported by: Mesonet
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Numerous 70 mph or higher wind gusts were reported by the Palomar Mt. mesonet station over a 6 hour period. Peak gusts to 75 mph occurred between 1820 and 1830PST. No damage reports were received for the mountains areas.

Heavy Snow, San Bernardino County Mountains

When: February 17, 2:00 PM PST to February 18, 3:00 AM PST
Where: San Bernardino County Mountains forecast zone
Reported by: Public
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Thirteen hour snow totals ranged from 12-24 inches above 6,500 ft, to a trace as low as 4,500 ft. Mt. Baldy and Mountain High ski resorts reported 16 to 24 inches of snow over a 13 hour period, while Green Valley Lake received 12 inches. Other snow totals included 8 inches in Wrightwood, 6 inches in Running Springs, and 3 inches in Big Bear.

High Surf, Orange County Coastal

When: February 17, 4:00 PM PST to February 19, 4:00 PM PST
Where: Orange County Coastal forecast zone
Reported by: Lifeguard
Coordinates: 33.677, -117.776 (the zone’s center; the record gives no point)

Lifeguards reported sets of 8-12 ft at Laguna Beach and 10-15 ft at San Clemente Beach. Sets near 10 ft were also reported in Newport Beach.

Debris Flow, San Bernardino

When: February 17, 4:00 PM PST to 6:00 PM PST
Where: San Bernardino County, 1.77 mi W of Cajon to 2.06 mi WSW of Cajon
Cause: Heavy Rain
Property damage: $500,000
Reported by: Broadcast Media
Coordinates: 34.320, -117.501

A big rig and car were caught in a mud flow near Highway 138 and Lone Pine Rd. Elsewhere along Highway 138 mud flows caused significant damage to area roadways.

Flash Flood, San Bernardino

When: February 17, 4:50 PM PST to 6:00 PM PST
Where: San Bernardino County, 0.97 mi ESE of Summit to 1.05 mi ESE of Summit
Cause: Heavy Rain
Property damage: $10,000
Reported by: Law Enforcement
Coordinates: 34.325, -117.404

California Highway Patrol reported water across all lanes of Highway 138 near Summit Valley Rd.

Thunderstorm Wind, Orange

When: February 17, 5:30 PM PST to 6:00 PM PST
Where: Orange County, 0.85 mi N of Laguna Beach to 2.09 mi E of Canyon Acres
Measured: 58 kt (67 mph) measured gust
Property damage: $25,000
Reported by: Mesonet
Coordinates: 33.532, -117.770

Roughly 20 trees were downed by convective winds in Laguna Beach. The nearby Laguna Beach mesonet station measured a peak gust of 67 mph at 1737PST.

Flash Flood, San Bernardino

When: February 17, 5:40 PM PST to 6:20 PM PST
Where: San Bernardino County, 1.26 mi SSW of Victorville to 1.25 mi S of Victorville
Cause: Heavy Rain
Deaths: 1 direct, 0 indirect
Injuries: 2 direct, 0 indirect
Property damage: $30,000
Reported by: Trained Spotter
Coordinates: 34.512, -117.304

Three vehicles swept from Rodeo Dr. near Pebble Beach Park. Swift water rescues were conducted to rescue 3 people. One fatality was reported.

Flood, San Bernardino

When: February 17, 5:40 PM PST to 6:40 PM PST
Where: San Bernardino County, 4.85 mi ESE of Phelan to 4.96 mi ESE of Phelan
Cause: Heavy Rain
Property damage: $15,000
Reported by: Law Enforcement
Coordinates: 34.405, -117.487

A jeep was submerged in a large sink hole at the intersection of Cedar St. and Chateau Rd. No water rescues required.

Flash Flood, Orange

When: February 17, 6:00 PM PST to 8:00 PM PST
Where: Orange County, 1.52 mi NNW of Santa Ana Gardens to 2.06 mi NNW of Santa Ana Gardens
Cause: Heavy Rain
Property damage: $50,000
Reported by: Law Enforcement
Coordinates: 33.739, -117.933

Flood waters from the Wintersburg Channel exceeded the channels banks, producing flooding in a mobile home park.

Flash Flood, San Bernardino

When: February 17, 7:45 PM PST to February 18, 2:45 AM PST
Where: San Bernardino County, 0.76 mi SW of Cajon to 1.51 mi WSW of Cajon
Cause: Heavy Rain
Property damage: $3.5 million
Reported by: Trained Spotter
Coordinates: 34.312, -117.480

Flood waters and related erosion caused a collapse of lane number 5 along Interstate 15. A fire truck and big rig were caught up and destroyed in the collapse. No injuries were reported but damages to the Interstate reached into the millions.

Flash Flood, San Bernardino

When: February 18, 12:20 AM PST to 1:10 AM PST
Where: San Bernardino County, 1.57 mi SE of Keenbrook to 1.74 mi SE of Keenbrook
Cause: Heavy Rain
Property damage: $10,000
Reported by: Fire Department/Rescue
Coordinates: 34.252, -117.463

Flood waters in the Cajon Pass submerged a vehicle along Keenbrook Rd. Three swift water rescues were conduced with no injuries reported.

The people who died

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
High Wind, San Diego County Coastal Areas	2017-02-17			Vehicle/Towed Trailer	Direct
Flash Flood, San Bernardino	2017-02-17			Vehicle/Towed Trailer	Direct

What these are

High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.
High Surf: Large waves breaking on the shore that caused damage, erosion or casualties.
Strong Wind: Non-thunderstorm winds below high wind criteria that nonetheless caused damage or casualties.
Heavy Snow: Snowfall reaching the local warning threshold without the other hazards of a winter storm.
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.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

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

The same day elsewhere

Every storm in California in 2017 Every state in 2017 This day in weather history Warnings in California, February 2017

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: 681056, 681051, 681057, 681052, 680852, 681049, 681050, 681054, 681087, 680853, 681131, 681058, 681048, 681029, 681031, 681044, 681033, 681034.