Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 38, NWS Denver/Boulder, CO

July 23, 2021Grand County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 23, 2021, 4:05 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 23, 2021, 4:05 PM MDT (22:05 UTC)
Expired: Jul 23, 2021, 7:00 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), 122 km from the middle of the area, began a volume at 22:09 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, 10.1 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: 21 J/kg
Mixed-layer CIN: -153 J/kg
Mixed-layer LCL: 1904 m above ground
0-6 km bulk shear: 5 kt
0-1 km storm-relative helicity: -41 m²/s²
0-3 km storm-relative helicity: -27 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

523 
WGUS55 KBOU 232205
FFWBOU
COC049-240100-
/O.NEW.KBOU.FF.W.0038.210723T2205Z-210724T0100Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
405 PM MDT Fri Jul 23 2021

The National Weather Service in Denver has issued a

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

* Until 700 PM MDT.

* At 405 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the northwest portion of the Williams Fork burn 
  area. Up to 0.5 inches of rain have fallen. Additional rainfall 
  amounts up to 0.5 inches 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...
  areas along and north of Kinney Creek within the Williams Fork 
  burn area.

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 3980 10590 3976 10589 3978 10594 3977 10598
      3978 10602 3987 10609 3988 10605 3991 10600
      3990 10598 3988 10597 3987 10596 3984 10599
      3982 10595 3980 10597

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

$$

Hiris

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 22, 6:51 PM MDT	Areal Flood Advisory	BOU	Adams, Denver, Jefferson	84 min
Jul 22, 7:10 PM MDT	Areal Flood Advisory	BOU	Douglas	95 min
Jul 23, 2:30 PM MDT	Special Weather Statement	BOU	Boulder	30 min
Jul 23, 2:41 PM MDT	Areal Flood Advisory	BOU	Grand	84 min
Jul 23, 2:50 PM MDT	Special Weather Statement	BOU	Summit	25 min
Jul 23, 4:11 PM MDT	Areal Flood Advisory	BOU	Clear Creek	2 hr
Jul 23, 4:51 PM MDT	Flash Flood Warning	BOU	Clear Creek, Gilpin	114 min

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.