Alert archive / Wyoming / Flash Flood Warnings in 2021

Flash Flood Warning 12, NWS Cheyenne, WY

September 3, 2021Laramie County, Wyoming

NWS Cheyenne, WY issued this flash flood warning at Sep 3, 2021, 5:25 PM MDT for Laramie County, Wyoming. It was in force for 3 hr. 2 reports 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 3, 2021, 5:25 PM MDT (23:25 UTC)
Expired: Sep 3, 2021, 8:20 PM MDT
In force: 3 hr
Issued by: NWS Cheyenne, WY
Area: Storm-based polygon
Flood severity: None

County Laramie County, WY

The radar

The Cheyenne radar (KCYS), 20 km from the middle of the area, began a volume at 23:27 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 3, 6:00 PM MDT	FLASH FLOOD	9 E Cheyenne, WY	COUNTY ROAD WAS FLOODED JUST EAST OF ARCHER.
Sep 3, 6:35 PM MDT	FLASH FLOOD	2 S Hillsdale, WY	PARKING LOT WAS FLOODED AT THE BURNS BROTHERS TRUCK STOP.

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

The nearest sounding before it

Denver, CO (KDNR), launched 12:00Z, 11.4 hours before the alert went out and 183 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: 39 J/kg
Mixed-layer CIN: -181 J/kg
Mixed-layer LCL: 1546 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: 55 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

285 
WGUS55 KCYS 032325
FFWCYS
WYC021-040230-
/O.NEW.KCYS.FF.W.0012.210903T2325Z-210904T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Cheyenne WY
525 PM MDT Fri Sep 3 2021

The National Weather Service in Cheyenne has issued a

* Flash Flood Warning for...
  South Central Laramie County in southeastern Wyoming...

* Until 830 PM MDT.

* At 525 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1.5 and 2 inches of 
  rain have fallen. Additional rainfall amounts of 0.25 to 0.75 
  inches are possible in the warned area. Flash flooding is ongoing 
  or expected to begin shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar.

  IMPACT...Flash flooding of small creeks and streams, urban
           areas, highways, streets and underpasses as well as
           other poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Cheyenne, Burns and Hillsdale.

This includes the following highways...
	Interstate 80 in Wyoming between mile markers 367 and 383.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 4111 10472 4113 10472 4116 10468 4119 10461
      4122 10454 4127 10444 4127 10436 4124 10433
      4118 10436 4113 10446 4111 10458 4109 10469
      4110 10471

FLASH FLOOD...RADAR INDICATED

$$

Charnick

2 follow-up statements

969 
WGUS75 KCYS 040105
FFSCYS

Flash Flood Statement
National Weather Service Cheyenne WY
705 PM MDT Fri Sep 3 2021

WYC021-040230-
/O.CON.KCYS.FF.W.0012.000000T0000Z-210904T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Laramie WY-
705 PM MDT Fri Sep 3 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 830 PM MDT THIS 
EVENING FOR SOUTH CENTRAL LARAMIE COUNTY...

At 705 PM MDT, Doppler radar indicated another round of 
thunderstorms producing heavy rain approaching the warned area. 
Between 1.5 and 2 inches of rain have already fallen from earlier 
storms. Additional rainfall amounts of 0.25 to 0.75 inches are 
possible in the warned area.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Several reports of localized flash flooding in the
         warned area.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Eastern Cheyenne, Burns and Hillsdale.

This includes the following highways...
	Interstate 80 in Wyoming between mile markers 367 and 383.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 4111 10472 4113 10472 4116 10468 4119 10461
      4122 10454 4127 10444 4127 10436 4124 10433
      4118 10436 4113 10446 4111 10458 4109 10469
      4110 10471

FLASH FLOOD...RADAR INDICATED

$$

MAC

942 
WGUS75 KCYS 040220
FFSCYS

Flash Flood Statement
National Weather Service Cheyenne WY
820 PM MDT Fri Sep 3 2021

WYC021-040230-
/O.CAN.KCYS.FF.W.0012.000000T0000Z-210904T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Laramie WY-
820 PM MDT Fri Sep 3 2021

...FLASH FLOOD WARNING IS CANCELLED FOR SOUTH CENTRAL LARAMIE 
COUNTY...

Flood waters have receded and the heavy rain has ended. Flooding is 
no longer expected to pose a threat.

LAT...LON 4111 10472 4113 10472 4116 10468 4119 10461
      4122 10454 4127 10444 4127 10436 4124 10433
      4118 10436 4113 10446 4111 10458 4109 10469
      4110 10471

$$

Cox

The office that day

Everything else NWS Cheyenne, WY issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 3, 4:14 AM MDT	Special Weather Statement	CYS	Niobrara	46 min
Sep 3, 1:38 PM MDT	Special Weather Statement	CYS	Laramie	37 min
Sep 3, 2:20 PM MDT	Special Weather Statement	CYS	Laramie	25 min
Sep 3, 2:47 PM MDT	Special Weather Statement	CYS	Laramie	43 min
Sep 3, 3:45 PM MDT	Special Weather Statement	CYS	Laramie	30 min
Sep 3, 3:53 PM MDT	Special Weather Statement	CYS	Laramie	37 min
Sep 3, 4:33 PM MDT	Special Weather Statement	CYS	Laramie	27 min
Sep 3, 4:45 PM MDT	Severe Thunderstorm Warning	CYS	Laramie	31 min
Sep 3, 5:14 PM MDT	Areal Flood Advisory	CYS	Laramie	12 min
Sep 3, 5:31 PM MDT	Severe Thunderstorm Warning	CYS	Goshen, Niobrara, Platte	26 min

Nearby

Flash Flood Warnings in Wyoming, 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.