Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 31, NWS Denver/Boulder, CO

July 21, 2021Larimer County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 21, 2021, 2:47 PM MDT for Larimer County, Colorado. It was in force for 103 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 21, 2021, 2:47 PM MDT (20:47 UTC)
Expired: Jul 21, 2021, 4:30 PM MDT
In force: 103 min
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Larimer County, CO

The radar

The Cheyenne radar (KCYS), 107 km from the middle of the area, began a volume at 20:50 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 12:00Z, 8.8 hours before the alert went out and 236 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 2182 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: -4 m²/s²
0-3 km storm-relative helicity: 13 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

257 
WGUS55 KBOU 212047
FFWBOU
COC069-212230-
/O.NEW.KBOU.FF.W.0031.210721T2047Z-210721T2230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
247 PM MDT Wed Jul 21 2021

The National Weather Service in Denver has issued a

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

* Until 430 PM MDT.

* At 247 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the western half of the Cameron Peak burn area. 
  Between 0.2 and 0.4 inches of rain have fallen. More is expected.  
  Flash flooding is ongoing or expected to begin shortly.  The 
  entire Cameron Peak burn area is now under a flash flood warning 
  until 4:30 PM MDT.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar.

  IMPACT...Flash flooding of small creeks and streams, gulches,
           roads, and poor drainage and low-lying areas.

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

This includes the following additional locations...
Bellaire Lake, Crown Point Road, The Upper Poudre Canyon, The 
Laramie River Road near Chambers Lake, Long Draw Road, Remote areas 
in the Cameron Peak Wilderness and Hague Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Heavy Rainfall will cause flash flooding of small creeks, streams, 
and ditches in the affected part of the Cameron Peak burn area. Rock 
slides or debris flows can also be expected across rural roads.

&&

LAT...LON 4077 10557 4046 10572 4051 10586 4052 10587
      4052 10588 4052 10589 4053 10591 4054 10591
      4055 10591 4056 10591 4057 10591 4057 10592
      4059 10593 4060 10593 4061 10594 4070 10591
      4079 10573

FLASH FLOOD...RADAR INDICATED

$$

RJK

1 follow-up statement

138 
WGUS75 KBOU 212227
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
427 PM MDT Wed Jul 21 2021

COC069-212237-
/O.EXP.KBOU.FF.W.0031.000000T0000Z-210721T2230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Larimer CO-
427 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 430 PM MDT THIS AFTERNOON FOR 
WEST CENTRAL LARIMER COUNTY...

The heavy rain has ended over the Cameron Peak burn area.  Flooding 
is no longer expected to pose a threat. Please continue to heed 
remaining road closures.

A Flash Flood Watch remains in effect until 800 PM MDT for A portion 
of north central Colorado.

LAT...LON 4077 10557 4046 10572 4051 10586 4052 10587
      4052 10588 4052 10589 4053 10591 4054 10591
      4055 10591 4056 10591 4057 10591 4057 10592
      4059 10593 4060 10593 4061 10594 4070 10591
      4079 10573

$$

RJK

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 20, 6:58 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Larimer	92 min
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, 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.