Alert archive / California / Flash Flood Warnings in 2021

Flash Flood Warning 3, NWS Sacramento, CA

October 24, 2021Nevada County, Placer County, California

NWS Sacramento, CA issued this flash flood warning at Oct 24, 2021, 5:45 PM PDT for Nevada County, Placer County, California. It was in force for 9 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Oct 24, 2021, 5:45 PM PDT (00:45 UTC)
Expired: Oct 25, 2021, 2:50 AM PDT
In force: 9 hr
Issued by: NWS Sacramento, CA
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

Counties Nevada County, CA, Placer County, CA

The radar

The Beale AFB radar (KBBX), 70 km from the middle of the area, began a volume at 00:44 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Oakland, CA (KOAK), launched 00:00Z, 0.8 hours before the alert went out and 187 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1 J/kg
Mixed-layer CIN: 0 J/kg
Mixed-layer LCL: 472 m above ground
0-6 km bulk shear: 83 kt
0-1 km storm-relative helicity: 377 m²/s²
0-3 km storm-relative helicity: 444 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

281 
WGUS56 KSTO 250045
FFWSTO
CAC057-061-251000-
/O.NEW.KSTO.FF.W.0003.211025T0045Z-211025T1000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Sacramento CA
545 PM PDT Sun Oct 24 2021

The National Weather Service in Sacramento has issued a

* Flash Flood Warning for...
  The River burn scar in...
  Placer County in central California...
  Nevada County in northern California...

* Until 300 AM PDT Monday.

* At 545 PM PDT, Doppler radar indicated heavy rain over the River 
  Burn Scar. Between 4 and 6.5 inches of rain have fallen over the 
  last 24 hours. Additional rainfall amounts of 2 to 5 inches are 
  possible in the warned area. Flash flooding is ongoing or expected 
  to begin shortly. An intense narrow band of heavy rain will impact 
  the burn scar area within the next 30 minutes.

Excessive rainfall over the warning area will cause mud slides near 
steep terrain. The mud slide can consist of rock, mud, vegetation 
and other loose materials.

  HAZARD...Life threatening flash flooding. Heavy rain producing
           flash flooding in and around the River Burn Scar.

  SOURCE...Radar and automated gauges.

  IMPACT...Life threatening flash flooding of areas in and around
           the River Burn Scar.

* Some locations that will experience flash flooding include...
  the River Burn Scar around the Bear River watershed in Placer and 
  Nevada Counties west to southwest of Rollins Lake.

If debris flows occur, this is an extremely dangerous quick moving 
and life-threatening situation. Avoid the area in case of flooding 
or possibility of evacuation order.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This is a life threatening situation. Heavy rainfall will cause 
extensive and severe flash flooding of creeks...streams...and 
ditches in the River Burn Scar. Severe debris flows can also be 
anticipated across roads. Roads and driveways may be washed away in 
places. If you encounter flood waters...climb to safety.

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

&&

LAT...LON 3911 12100 3912 12099 3913 12099 3914 12098
      3915 12097 3914 12097 3913 12096 3911 12096
      3911 12097 3910 12098 3909 12098 3909 12099
      3910 12099

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

IDM

1 follow-up statement

911 
WGUS76 KSTO 250950
FFSSTO

Flash Flood Statement
National Weather Service Sacramento CA
250 AM PDT Mon Oct 25 2021

CAC057-061-251000-
/O.CAN.KSTO.FF.W.0003.000000T0000Z-211025T1000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Nevada CA-Placer CA-
250 AM PDT Mon Oct 25 2021

...FLASH FLOOD WARNING IS CANCELLED FOR PLACER AND NEVADA COUNTIES...

The heavy rain has ended over the River Fire burn scar. Flash 
flooding is no longer expected to pose an immediate threat. Minor 
debris flows will still be possible early this morning. Please 
continue to heed remaining road closures.

A Flash Flood Watch remains in effect until 500 AM PDT.

LAT...LON 3911 12100 3912 12099 3913 12099 3914 12098
      3915 12097 3914 12097 3913 12096 3911 12096
      3911 12097 3910 12098 3909 12098 3909 12099
      3910 12099

$$

DFR

The office that day

Everything else NWS Sacramento, CA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 25, 12:06 AM PDT	Areal Flood Advisory	STO	Calaveras, San Joaquin, Stanislaus, Tuolumne	26 hr
Oct 25, 4:44 AM PDT	Areal Flood Advisory	STO	Tehama	4 hr
Oct 25, 12:59 PM PDT	Special Weather Statement	STO	Butte	31 min
Oct 25, 1:37 PM PDT	Special Weather Statement	STO	Butte	38 min

Nearby

Flash Flood Warnings in California, 2021 Every flash flood warning in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.