Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 34, NWS Denver/Boulder, CO

July 21, 2021Grand County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 21, 2021, 6:11 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 21, 2021, 6:11 PM MDT (00:11 UTC)
Expired: Jul 21, 2021, 9:15 PM MDT
In force: 3 hr
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Grand County, CO

The radar

The Denver radar (KFTG), 144 km from the middle of the area, began a volume at 00:13 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 00:00Z, 0.2 hours before the alert went out and 242 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: 166 J/kg
Mixed-layer CIN: -10 J/kg
Mixed-layer LCL: 3273 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: -1 m²/s²
0-3 km storm-relative helicity: 29 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

The text

As transmitted.

784 
WGUS55 KBOU 220011
FFWBOU
COC049-220315-
/O.NEW.KBOU.FF.W.0034.210722T0011Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Denver has issued a

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

* Until 915 PM MDT.

* At 611 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 0.6 and 1.4 inches of 
  rain have fallen. Flash flooding is ongoing or expected to begin 
  shortly.  Law enforcement indicating there were multiple mudslides 
  along State Road 125, and it remains closed.

  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...
  mainly rural areas of North Central Grand County

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 East Troublesome burn area. Some areas affected 
include the North Inlet in the town of Grand Lake, the burned areas 
on the west side of Rocky Mountain National Park, the Colorado River 
above Shadow Mountain Reservoir, the Willow Creek valley along 
Highway 125, Drowsy Water Creek, and the East Troublesome Creek 
valley. Rock slides or debris flows can also be expected across 
rural roads.

&&

LAT...LON 4036 10599 4017 10587 4010 10593 4010 10617
      4017 10627 4026 10628 4033 10622 4033 10619
      4034 10618 4034 10616 4033 10614 4035 10610
      4035 10608 4037 10603

FLASH FLOOD...RADAR INDICATED

$$

RJK

2 follow-up statements

252 
WGUS75 KBOU 220056
FFSBOU

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

COC049-220315-
/O.CON.KBOU.FF.W.0034.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
656 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 915 PM MDT THIS 
EVENING FOR NORTH CENTRAL GRAND COUNTY...

At 656 PM MDT, Doppler radar indicated thunderstorms producing heavy 
rain across the warned area. 0.3 to 0.5 inches of rain have fallen 
in the past hour. Storms are moving east southeast at 10 to 15 mph. 
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, gulches,
         roads, and poor drainage and low-lying areas.

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

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 East Troublesome burn area. Some areas affected 
include the North Inlet in the town of Grand Lake, the burned areas 
on the west side of Rocky Mountain National Park, the Colorado River 
above Shadow Mountain Reservoir, the Willow Creek valley along 
Highway 125, Drowsy Water Creek, and the East Troublesome Creek 
valley. Rock slides or debris flows can also be expected across 
rural roads.

&&

LAT...LON 4036 10599 4017 10587 4010 10593 4010 10617
      4017 10627 4026 10628 4033 10622 4033 10619
      4034 10618 4034 10616 4033 10614 4035 10610
      4035 10608 4037 10603

FLASH FLOOD...RADAR INDICATED

$$

TH

338 
WGUS75 KBOU 220313
FFSBOU

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

COC049-220323-
/O.EXP.KBOU.FF.W.0034.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
913 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 915 PM MDT THIS EVENING FOR 
NORTH CENTRAL GRAND COUNTY...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures. More light 
rain showers are expected tonight.

LAT...LON 4036 10599 4017 10587 4010 10593 4010 10617
      4017 10627 4026 10628 4033 10622 4033 10619
      4034 10618 4034 10616 4033 10614 4035 10610
      4035 10608 4037 10603

$$

Danielson

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, 6:19 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
Jul 22, 3:13 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Grand	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.