Name: Debris Flow in California, April 14, 2011
Start: 2011-04-14T16:30
End: 2011-04-14T16:31
Location: California

Where it happened

Every event with a place to put it; 1 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

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The toll

Deaths: 0
Injuries: 0
Property damage: $100,000
Crop damage: None recorded
Events: 1

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 MTR wrote it up.

Storms from March provided the necessary moisture to cause a hillside to fail producing a debris flow weeks later.

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 Francisco Bay Area, CA wrote its last area forecast discussion before the first event at Apr 14, 4:15 PM PST, 15 minutes earlier.

Area forecast discussion, Apr 14, 4:15 PM PST, 15 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
515 PM PDT THU APR 14 2011

.DISCUSSION...AS OF 2:55 PM PDT THURSDAY...TEMPERATURES ARE RUNNING
AROUND 2 DEGREES WARMER THAN YESTERDAY AT THIS HOUR. MOST LIKELY THIS
WARM UP WAS DUE TO SLIGHTLY CLEARER SKIES ACROSS THE FORECAST AREA.
THE LATEST VISIBLE SATELLITE IMAGE IS STILL SHOWING HIGH CLOUDS
SPILLING OVER THE RIDGE OF HIGH PRESSURE CURRENTLY PARKED OVER THE
EASTERN PACIFIC. AMSU DATA IS ALSO STILL SHOWING A TRAIL OF MOIST
AIR PUSHING TOWARD THE WEST COAST. AMSU PW VALUES ARE AROUND 1.5
INCHES AT 149 DEGREES WEST AND 34 DEGREES NORTH.

ACCORDING TO THE 1200Z OPERATIONAL GFS THE A FORE MENTIONED PLUME OF
MOISTURE WILL ARRIVE IN SONOMA COUNTY BETWEEN 0300Z AND 0600Z
SATURDAY. AT WHICH POINT PRECIPITABLE WATER VALUES WILL BE ON THE
ORDER OF 1.12 TO 1.21 INCHES WITH GENTLE ISENTROPIC ASCENT. THIS
VALUE IS SLIGHTLY DRIER THAN WHAT THE 0600Z RUN WAS ADVERTISING
THIS MORNING. THIS WILL STILL RESULT IN A GOOD CHANCE OF LIGHT RAIN
FOR THE COASTAL RANGES FRIDAY NIGHT INTO EARLY SATURDAY AFTERNOON.
THEREFORE HAVE BUMPED UP THE POP GRIDS SLIGHTLY FOR THAT PERIOD IN
THE AFTERNOON FORECAST PACKAGE. SOME LIGHT PRECIPITATION MAY ALSO
REACH INTO THE BAY AREA AS WELL. SOUTH OF THE SAN FRANCISCO BAY AREA
WILL BE DRY THIS WEEKEND WITH MID 60S ALONG THE COAST AND MID 70S TO
LOW 80S EXPECTED IN THE INLAND VALLEYS.

BOTH THE 12Z RUNS OF ECMWF AND OPERATIONAL GFS SHOW A WEAK TROUGH OF
LOW PRESSURE DIVING INTO THE PACIFIC NORTHWEST SUNDAY NIGHT MONDAY
MORNING. THIS TROUGH WILL SLIDE A BOUNDARY OVER THE AREA ONCE
AGAIN BRINGING A POSSIBILITY OF LIGHT RAIN. THEREFORE HAVE ALSO
BUMPER THE POPS UP SUNDAY NIGHT INTO MONDAY MORNING.

&&

.AVIATION...AS OF 5:15 PM THURSDAY...VFR CONDITIONS EXPECTED THROUGH
THE FORECAST PERIOD WITH MAINLY HIGH CLOUDS AND DECREASING WEST
WINDS THROUGH THE EVENING AND OVERNIGHT HOURS.

VICINITY OF KSFO...VFR THROUGH TONIGHT WITH INCREASING HIGH CLOUDS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...VFR THROUGH TONIGHT. WEST WINDS
DECREASING THIS EVENING BECOMING EASTERLY OVERNIGHT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
    .TNGT...SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM.
            SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
&&

PUBLIC FORECAST: LARRY
AVIATION/MARINE: CW

The radar

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

Open the radar archive at this moment

Event by event

1 debris flow. Local standard time, as filed.

Debris Flow, Southern Monterey Bay and Big Sur Coast

When: April 14, 4:30 PM PST to 4:31 PM PST
Where: Southern Monterey Bay and Big Sur Coast forecast zone
Property damage: $100,000
Reported by: Emergency Manager
Coordinates: 36.240, -121.309 (the zone’s center; the record gives no point)

A hillside south of Big Sur gave way weeks after the last heavy rainfall ended. A debris flow occurred 6.2 miles north of the San Luis Obispo County line along State Highway One. The road remained closed until June 9, 2011.

What these are

Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.

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

The same day elsewhere

More

Every storm in California in 2011 Every state in 2011 This day in weather history Warnings in California, April 2011

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: 304100.