Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 28, NWS Denver/Boulder, CO

July 20, 2021Larimer County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 20, 2021, 6:58 PM MDT for Larimer County, Colorado. It was in force for 92 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Jul 20, 2021, 6:58 PM MDT (00:58 UTC)
Expired: Jul 20, 2021, 8:30 PM MDT
In force: 92 min
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Larimer County, CO

The radar

The Cheyenne radar (KCYS), 95 km from the middle of the area, began a volume at 01:01 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.

The nearest sounding before it

Denver, CO (KDNR), launched 00:00Z, 1.0 hours before the alert went out and 231 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: 99 J/kg
Mixed-layer CIN: -49 J/kg
Mixed-layer LCL: 3076 m above ground
0-6 km bulk shear: 6 kt
0-1 km storm-relative helicity: -2 m²/s²
0-3 km storm-relative helicity: 36 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

304 
WGUS55 KBOU 210058
FFWBOU
COC069-210230-
/O.NEW.KBOU.FF.W.0028.210721T0058Z-210721T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
658 PM MDT Tue Jul 20 2021

The National Weather Service in Denver has issued a

* Flash Flood Warning for...
  Central Larimer County in north central Colorado...

* Until 830 PM MDT.

* At 658 PM MDT, local law enforcement reported flash flooding 
  across the Cameron Peak burn area along Highway 14. Flash flooding 
  is already occurring.

  HAZARD...Life threatening flash flooding. Heavy rain produced
           flash flooding.

  SOURCE...Law enforcement reported.

  IMPACT...Life threatening flash flooding of creeks and streams,
           roads, and low lying areas.

* Some locations that will experience flash flooding include...
  Kinikinik and Rustic.

This includes the following additional locations...
Gulches along Highway 14 near and above Rustic, Rising water and 
large debris in the Poudre River and The Upper Poudre Canyon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Move to higher ground now. Act quickly to protect your life.

THIS IS A LIFE THREATENING SITUATION! Heavy Rainfall has caused 
extensive and severe flooding of creeks, streams, roads and culverts 
in the affected part of the Cameron Peak burn area. Rock slides or 
debris flows can also be expected across roads in the warning area.

&&

LAT...LON 4070 10557 4069 10570 4071 10574 4067 10578
      4066 10580 4066 10581 4064 10580 4055 10587
      4055 10588 4064 10581 4066 10582 4067 10581
      4068 10579 4071 10575 4072 10574 4070 10568
      4071 10564 4070 10561

FLASH FLOOD...OBSERVED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

Direnzo

1 follow-up statement

193 
WGUS75 KBOU 210225
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
825 PM MDT Tue Jul 20 2021

COC069-210235-
/O.EXP.KBOU.FF.W.0028.000000T0000Z-210721T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Larimer CO-
825 PM MDT Tue Jul 20 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 830 PM MDT THIS EVENING FOR 
CENTRAL LARIMER COUNTY...

Flood waters have receded. The heavy rain has ended. Flooding is no 
longer expected to pose a threat. Please continue to heed remaining 
road closures.

LAT...LON 4070 10557 4069 10570 4071 10574 4067 10578
      4066 10580 4066 10581 4064 10580 4055 10587
      4055 10588 4064 10581 4066 10582 4067 10581
      4068 10579 4071 10575 4072 10574 4070 10568
      4071 10564 4070 10561

$$

Direnzo

The office that day

Everything else NWS Denver/Boulder, CO issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 7:09 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Larimer	81 min
Jul 21, 3:18 AM MDT	Flash Flood Watch	BOU	Boulder, Grand, Jackson, Larimer	17 hr
Jul 21, 1:30 PM MDT	Flash Flood Warning	BOU	Larimer	3 hr
Jul 21, 1:56 PM MDT	Areal Flood Advisory	BOU	Grand	3 hr
Jul 21, 2:31 PM MDT	Areal Flood Advisory	BOU	Park	119 min
Jul 21, 2:44 PM MDT	Special Weather Statement	BOU	Teller	46 min
Jul 21, 2:47 PM MDT	Flash Flood Warning	BOU	Larimer	103 min
Jul 21, 3:16 PM MDT	Flash Flood Warning	BOU	Grand, Larimer	3 hr
Jul 21, 3:22 PM MDT	Areal Flood Advisory	BOU	Park	69 min
Jul 21, 4:40 PM MDT	Areal Flood Advisory	BOU	Douglas	65 min
Jul 21, 5:06 PM MDT	Flash Flood Warning	BOU	Clear Creek	3 hr

Nearby

Flash Flood Warnings in Colorado, 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.