Debris Flow and High Wind in California, September 20 to 21, 2017

Name: Debris Flow and High Wind in California, September 20 to 21, 2017
Start: 2017-09-20T21:27
End: 2017-09-21T20:26
Location: California

September 20 to 21, 2017 · NWS HNX · 5 events in 4 counties and zones

Where it happened

Every event with a place to put it. 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: None recorded
Crop damage: None recorded
Events: 5

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 HNX wrote it up.

A cold and moist upper low which originated in the Gulf of Alaska pushed into California on September 21 bringing widespread precipitation, increased winds and much cooler than normal temperatures to the area. Winds picked up across the area again on the evening of September 20 and continued through the afternoon of September 21 with the strongest observed gusts being observed at the indicator ridge top sites in the Kern County Mountains. In addition, widespread precipitation impacted to area on the 21st with several locations in the San Joaquin Valley measuring a few tenths of an inch of rainfall while several locations in the Southern Sierra Nevada from Yosemite Park southward to Fresno County picked up between an inch and an inch and a half of liquid precipitation. The precipitation fell as snow above 11000 feet during the early morning hours of the 21st. the snow level lowered to around 7000 feet in Yosemite Park by late morning. Tuolumne Meadows measures three inches of new snowfall while State Route 120 through Tioga Pass was shut down due to accumulating snow.

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 Hanford, CA wrote its last area forecast discussion before the first event at Sep 20, 5:25 PM PST, 4 hours 2 minutes earlier.

Area forecast discussion, Sep 20, 5:25 PM PST, 4 hours 2 minutes before

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
625 PM PDT Wed Sep 20 2017

.SYNOPSIS...
Below normal temperatures will continue this week with further
cooling on Thursday. Breezy to gusty wind conditions will
continue through Thursday, especially through and below mountain
passes. Showers are possible over the mountains Wednesday night
through Friday with light snow above 8000 feet. A warming trend is
expected this weekend through the middle of next week with mostly
clear skies.

&&

.DISCUSSION...
Due to strong west to east orientated jet moving southward, have
gone ahead and updated the forecast for strong winds in the Kern
County mountains and desert areas and gusty winds on the west side
of the SJV. Also, issued a high wind warning for the Kern County
mountains and desert areas through 11 PM Thursday. A wind advisory
is now in effect for the western parts of the SJV also through 11
PM Thursday.

&&

.PREV DISCUSSION... /issued 305 PM PDT Wed Sep 20 2017/

DISCUSSION...
A strong upper trough will push inland tonight and Thursday
bringing a re-enforcing shot of cooler air along with breezy
conditions through Thursday across most of our area. Highs in the
San Joaquin Valley Thursday will be 5 to 10 degrees cooler than
Wednesday, while Sierra and Kern desert locations will be 10 to
20 degrees cooler. This system will also bring another period of
breezy to locally windy conditions to the Kern County mountains
and desert as well as a brief shot of precipitation to the
Southern Sierra Nevada mainly north of Kings Canyon.

Precipitation amounts up to a quarter inch are possible in the
southern Sierra Nevada north of Kings Canyon. Snow levels are
expected to be around 11000 feet at the onset of precipitation
later this evening lowering to around 7000 feet by Thursday
afternoon. 1-2 inches of snow is possible along the higher peaks
in the southern Sierra Nevada.

The trough is progged to remain over CA on Friday as the main
upper low center lifts slowly northward. Temperatures will remain
much below normal on Friday and there will be enough instability
along the Southern Sierra crest Friday afternoon and evening for
a few snow showers.

Temperatures will recover over the weekend as the trough moves
east and high pressure builds inland. The medium range models are
in good agreement with an upper ridge strengthening over CA
through the middle of next week. This will result in temperatures
rising to slightly above normal values by next Tuesday. There is
little in the way of moisture from Saturday onward so expect dry
weather to prevail from the weekend through the middle of next
week.

&&

.AVIATION...
Showers spreading over the southern Sierra Nevada and Kern County
mountains after 00Z Thursday, bringing areas of MVFR and local
terrain obscurations. Otherwise, VFR conditions can be expected over
the Central CA interior during the next 24 hours.

&&

.AIR QUALITY ISSUES...
None.

&&

.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is high.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...
High Wind Warning until 11 PM PDT Thursday ABOVE 1500 FEET FOR
THE CAZ095-098-099.

Wind Advisory until 11 PM PDT Thursday CAZ089-091.

&&

public...Andersen
avn/fw...MV
prev discussion...Bentzien
synopsis...Andersen

weather.gov/hanford

In the hours before

Local storm report, Sep 20, 7:22 PM PST, 2 hours 5 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
822 PM PDT WED SEP 20 2017

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

0802 PM     NON-TSTM WND GST 12 W LOS BANOS          37.05N 121.05W
09/20/2017  M35 MPH          MERCED             CA   MESONET

            MESONET STATION SLRC1, SAN LUIS DAM.

&&

JA

Local storm report, Sep 20, 8:00 PM PST, 1 hour 27 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
900 PM PDT WED SEP 20 2017

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

0835 PM     NON-TSTM WND GST 5 NW MOJAVE             35.11N 118.24W
09/20/2017  M52 MPH          KERN               CA   MESONET

            MESONET STATION AU563, CACHE CREEK CHP ON
            58.

&&

JA

Local storm report, Sep 20, 8:13 PM PST, 1 hour 14 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
913 PM PDT WED SEP 20 2017

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

0850 PM     NON-TSTM WND GST 18 SW GUSTINE           37.04N 121.19W
09/20/2017  M35 MPH          MERCED             CA   MESONET

            MESONET STATION AT423, PACHECO PASS.

&&

JA

Local storm report, Sep 20, 8:25 PM PST, 1 hour 2 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
925 PM PDT WED SEP 20 2017

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

0914 PM     NON-TSTM WND GST 18 SW GUSTINE           37.04N 121.19W
09/20/2017  M39 MPH          MERCED             CA   MESONET

            MESONET STATION AT423, PACHECO PASS.

&&

JA

Local storm report, Sep 20, 8:47 PM PST, 40 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
947 PM PDT WED SEP 20 2017

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

0926 PM     NON-TSTM WND GST 2 NW INDIAN WELLS VALLE 35.69N 117.89W
09/20/2017  M51 MPH          KERN               CA   MESONET

            MESONET STATION IWLC1, INDIAN WELLS CANYON.

&&

JA

Local storm report, Sep 20, 9:19 PM PST, 8 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
1019 PM PDT WED SEP 20 2017

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

1006 PM     NON-TSTM WND GST 18 SW GUSTINE           37.04N 121.19W
09/20/2017  M41 MPH          MERCED             CA   MESONET

            MESONET STATION AT423, PACHECO PASS.

&&

JA

The radar

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

Open the radar archive at this moment

Event by event

4 high wind, 1 debris flow. Local standard time, as filed.

High Wind, Kern Cty Mtns

When: September 20, 9:27 PM PST
Where: Kern Cty Mtns forecast zone
Measured: 74 kt (85 mph) measured gust
Reported by: RAWS

The Bird Springs Pass RAWS reported a maximum wind gust of 85 mph.

High Wind, Kern Cty Mtns

When: September 21, 1:32 AM PST
Where: Kern Cty Mtns forecast zone
Measured: 54 kt (62 mph) measured gust
Reported by: RAWS

The Blue Max RAWS reported a maximum wind gust of 62 mph.

Debris Flow, Mariposa

When: September 21, 3:00 AM PST to 5:17 AM PST
Where: Mariposa County, 1.4 mi S of Foresta to 1.54 mi SSE of Foresta
Cause: Heavy Rain
Reported by: Park/Forest Service
Coordinates: 37.680, -119.751

National Park Service employees at Yosemite National Park reported a rock slide at Dog Rock that closed State Route 140 2 miles east of El Portal due to large boulders on the road.

High Wind, Tulare Cty Mtns

When: September 21, 5:10 AM PST
Where: Tulare Cty Mtns forecast zone
Measured: 51 kt (59 mph) measured gust
Reported by: RAWS

The Bear Peak RAWS reported a maximum wind gust of 59 mph.

High Wind, Indian Wells Vly

When: September 21, 8:26 PM PST
Where: Indian Wells Vly forecast zone
Measured: 52 kt (60 mph) measured gust
Reported by: RAWS

The Indian Wells Canyon RAWS reported a maximum wind gust of 60 mph.

What these are

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.

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, September 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: 720888, 720887, 720892, 720890, 720889.