Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 37, NWS Denver/Boulder, CO

July 22, 2021Grand County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 22, 2021, 3:13 PM MDT for Grand County, Colorado. It was in force for 3 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: Jul 22, 2021, 3:13 PM MDT (21:13 UTC)
Expired: Jul 22, 2021, 6:15 PM MDT
In force: 3 hr
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Grand County, CO

The radar

The Denver radar (KFTG), 121 km from the middle of the area, began a volume at 21:16 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

Grand Junction, CO (KGJT), launched 12:00Z, 9.2 hours before the alert went out and 230 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: 1949 m above ground
0-6 km bulk shear: 4 kt
0-1 km storm-relative helicity: 42 m²/s²
0-3 km storm-relative helicity: -22 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

336 
WGUS55 KBOU 222113
FFWBOU
COC049-230015-
/O.NEW.KBOU.FF.W.0037.210722T2113Z-210723T0015Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
313 PM MDT Thu Jul 22 2021

The National Weather Service in Denver has issued a

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

* Until 615 PM MDT.

* At 313 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the Williams Fork burn area. Up to 0.3 inches of 
  rain have fallen. Additional rainfall amounts of 0.25 to 1 inch 
  are possible in the warned area. Flash flooding is ongoing or 
  expected to begin shortly.

  HAZARD...Life threatening flash flooding. Thunderstorms
           producing flash flooding.

  SOURCE...Radar.

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

* Some locations that will experience flash flooding include...
  mainly rural areas of South Central Grand County

This includes the following streams and drainages...
  West Fork Clear Creek, Bobtail Creek, South Fork Williams Fork, 
  Keyser Creek, Boham Creek, Middle Fork Williams Fork, Darling 
  Creek, Kinney Creek, Williams Fork, Ute Creek and Saint Louis 
  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 Williams Fork burn area. Rock slides or debris 
flows can also be expected across rural roads. Flooding is possible 
downstream of the burn area along the Williams Fork.

&&

LAT...LON 3975 10588 3976 10592 3977 10594 3977 10597
      3977 10601 3981 10606 3987 10610 3988 10607
      3991 10600 3989 10595 3985 10598 3983 10596
      3979 10596 3980 10590 3976 10588

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

$$

Hiris

1 follow-up statement

471 
WGUS75 KBOU 230010
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
610 PM MDT Thu Jul 22 2021

COC049-230020-
/O.EXP.KBOU.FF.W.0037.000000T0000Z-210723T0015Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
610 PM MDT Thu Jul 22 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 615 PM MDT THIS EVENING FOR 
SOUTH CENTRAL GRAND COUNTY...

The heavy rain has ended, and no flooding reports have been 
received. Flooding is no longer expected to pose a threat.

LAT...LON 3975 10588 3976 10592 3977 10594 3977 10597
      3977 10601 3981 10606 3987 10610 3988 10607
      3991 10600 3989 10595 3985 10598 3983 10596
      3979 10596 3980 10590 3976 10588

$$

Hiris

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 21, 6:01 PM MDT	Areal Flood Advisory	BOU	Douglas, Elbert	89 min
Jul 21, 6:11 PM MDT	Flash Flood Warning	BOU	Grand	3 hr
Jul 21, 6:19 PM MDT	Flash Flood Warning	BOU	Douglas	3 hr
Jul 22, 11:15 AM MDT	Areal Flood Advisory	BOU	Larimer	2 hr
Jul 22, 11:44 AM MDT	Areal Flood Advisory	BOU	Larimer	2 hr
Jul 22, 12:04 PM MDT	Areal Flood Advisory	BOU	Larimer	116 min
Jul 22, 2:14 PM MDT	Areal Flood Advisory	BOU	Grand	22 min
Jul 22, 2:15 PM MDT	Flash Flood Watch	BOU	Boulder, Clear Creek, Gilpin, Grand, Jackson, Jefferson and 3 more	30 hr
Jul 22, 2:36 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Grand	5 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.