Alert archive / South Dakota / Flash Flood Warnings in 2021

Flash Flood Warning 2, NWS Rapid City, SD

September 2, 2021Mellette County, Todd County, Tripp County, South Dakota

NWS Rapid City, SD issued this flash flood warning at Sep 2, 2021, 4:00 AM CDT for Mellette County, Todd County, Tripp County, South Dakota. It was in force for 3 hr. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Sep 2, 2021, 4:00 AM CDT (09:00 UTC)
Expired: Sep 2, 2021, 7:00 AM CDT
In force: 3 hr
Issued by: NWS Rapid City, SD
Area: Storm-based polygon
Flood severity: None

Counties Mellette County, SD, Todd County, SD, Tripp County, SD

The radar

The North Platte radar (KLNX), 188 km from the middle of the area, began a volume at 09:01 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.

What was reported inside it

Time	Report	Where	Remark
Sep 2, 7:00 AM CDT	HEAVY RAIN 2.55	13 Ene White River, SD	24-HOUR RAINFALL.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Rapid City, SD (KUNR), launched 00:00Z, 9.0 hours before the alert went out and 195 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: 549 J/kg
Mixed-layer CIN: -82 J/kg
Mixed-layer LCL: 1203 m above ground
0-6 km bulk shear: 55 kt
0-1 km storm-relative helicity: -34 m²/s²
0-3 km storm-relative helicity: 71 m²/s²
Significant tornado parameter: -0.0
Supercell composite: -0.7

Open this sounding in Storm Lab

The text

As transmitted.

224 
WGUS53 KUNR 020900
FFWUNR
SDC095-121-123-021200-
/O.NEW.KUNR.FF.W.0002.210902T0900Z-210902T1200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Rapid City SD
400 AM CDT Thu Sep 2 2021

The National Weather Service in Rapid City has issued a

* Flash Flood Warning for...
  Northwestern Todd County in south central South Dakota...
  Northwestern Tripp County in south central South Dakota...
  Central Mellette County in south central South Dakota...

* Until 700 AM CDT.

* At 358 AM CDT, Doppler radar indicated thunderstorms producing
  heavy rain across the warned area. Up to three inches of rain have
  already fallen. Flash flooding is ongoing or expected to begin
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar indicated.

  IMPACT...Flooding of small creeks and streams, urban areas, 
           highways, streets and underpasses as well as other 
           drainage and low lying areas.

* Some locations that will experience flooding include...
  White River, Parmelee, Horse Creek, Swift Bear and Intersection of
  Highway 83 and White River.

Additional rainfall of up to an inch is possible in the warned area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Be especially cautious at night when it is harder to recognize the
dangers of flooding.

&&

LAT...LON 4348 10111 4375 10064 4374 10064 4377 10058
      4373 10055 4373 10046 4372 10047 4374 10036
      4370 10029 4371 10023 4369 10021 4371 10018
      4369 10011 4358 10024 4350 10053 4330 10103

FLASH FLOOD...RADAR INDICATED

$$

Richards

1 follow-up statement

098 
WGUS73 KUNR 021159
FFSUNR

Flash Flood Statement
National Weather Service Rapid City SD
659 AM CDT Thu Sep 2 2021

SDC095-121-123-021204-
/O.EXP.KUNR.FF.W.0002.000000T0000Z-210902T1200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Todd SD-Tripp SD-Mellette SD-
659 AM CDT Thu Sep 2 2021

...THE FLASH FLOOD WARNING FOR NORTHWESTERN TODD...NORTHWESTERN TRIPP
AND CENTRAL MELLETTE COUNTIES WILL EXPIRE AT 700 AM CDT...

Although the threat of widespread heavy rain has ended, rain showers 
will continue over the area for another hour or so, with an 
additional third of an inch of rain possible.

Runoff from the heavy rain overnight will continue to move 
downstream, with rapid water level rises expected on area rivers and 
streams. Do not drive through any areas where water is flowing 
across the road.

LAT...LON 4348 10111 4375 10064 4374 10064 4377 10058
      4373 10055 4373 10046 4372 10047 4374 10036
      4370 10029 4371 10023 4369 10021 4371 10018
      4369 10011 4358 10024 4350 10053 4330 10103

$$

Richards

The office that day

Everything else NWS Rapid City, SD issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 1, 9:36 PM CDT	Special Weather Statement	UNR	Bennett	39 min
Sep 1, 10:04 PM CDT	Special Weather Statement	UNR	Oglala Lakota	26 min
Sep 1, 10:24 PM CDT	Special Weather Statement	UNR	Bennett	51 min
Sep 1, 10:26 PM CDT	Special Weather Statement	UNR	Jackson	34 min
Sep 1, 10:54 PM CDT	Special Weather Statement	UNR	Bennett	36 min
Sep 1, 11:16 PM CDT	Special Weather Statement	UNR	Mellette	44 min
Sep 1, 11:24 PM CDT	Special Weather Statement	UNR	Bennett	51 min
Sep 2, 12:22 AM CDT	Special Weather Statement	UNR	Mellette, Todd	38 min
Sep 2, 12:48 AM CDT	Areal Flood Advisory	UNR	Mellette, Todd, Tripp	6 hr

Nearby

Flash Flood Warnings in South Dakota, 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.