Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 36, NWS Denver/Boulder, CO

July 22, 2021Grand County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 22, 2021, 2:36 PM MDT for Grand County, Colorado. It was in force for 5 hr. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Jul 22, 2021, 2:36 PM MDT (20:36 UTC)
Expired: Jul 22, 2021, 8:00 PM MDT
In force: 5 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), 137 km from the middle of the area, began a volume at 20:37 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.

What was reported inside it

Time	Report	Where	Remark
Jul 22, 3:41 PM MDT	FLASH FLOOD	10 Nne Hot Sulphur Spri, CO	DEBRIS FLOW OVER COLORADO HIGHWAY 125 NEAR MILE MARKER 7. IT CAUSED THE CLOSURE OF THE HIGHWAY.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Denver, CO (KDNR), launched 12:00Z, 8.6 hours before the alert went out and 241 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: 1 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 2242 m above ground
0-6 km bulk shear: 0 kt
0-1 km storm-relative helicity: -11 m²/s²
0-3 km storm-relative helicity: 2 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

865 
WGUS55 KBOU 222036
FFWBOU
COC049-222330-
/O.NEW.KBOU.FF.W.0036.210722T2036Z-210722T2330Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Denver has issued a

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

* Until 530 PM MDT.

* At 236 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the East Troublesome burn area. Between 0.2 and 
  0.6 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...
  Highway 125 between mile marker 5 and 15.

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 10595 4034 10588 4022 10587 4015 10589
      4012 10593 4012 10599 4010 10607 4013 10613
      4022 10617 4029 10616 4034 10613 4035 10610
      4035 10608 4037 10603 4037 10601 4036 10601
      4036 10599 4035 10596

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

$$

Hiris

3 follow-up statements

688 
WGUS75 KBOU 222150
FFSBOU

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

COC049-222330-
/O.CON.KBOU.FF.W.0036.000000T0000Z-210722T2330Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
350 PM MDT Thu Jul 22 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 530 PM MDT THIS 
AFTERNOON FOR NORTH CENTRAL GRAND COUNTY...

At 350 PM MDT, Emergency management reported flash flooding. A 
mudslide was reported on CO-125 near mile marker 7. Between 0.5 and 
1.5 inches of rain fell within the East Troublesome burn area. Flash 
flooding is already occurring.

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

SOURCE...Emergency management reported.

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

Some locations that will experience flash flooding include...
  Highway 125 between mile marker 5 and 15.

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 10595 4034 10588 4022 10587 4015 10589
      4012 10593 4012 10599 4010 10607 4013 10613
      4022 10617 4029 10616 4034 10613 4035 10610
      4035 10608 4037 10603 4037 10601 4036 10601
      4036 10599 4035 10596

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

$$

Hiris

610 
WGUS55 KBOU 222310
FFWBOU
COC049-230200-
/O.EXT.KBOU.FF.W.0036.000000T0000Z-210723T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Denver has extended the

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

* Until 800 PM MDT.

* At 510 PM MDT, heavy rain is occurring on the southern portion of 
  the East Troublesome burn area. Up to 0.5 inches of new rainfall 
  is possible in this area. Flash Flooding has already occurred on 
  Highway 125, which remains closed due to a mudslide near milepost 
  7.

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

  SOURCE...Emergency management reported.

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

* Some locations that will experience flash flooding include...
  Highway 125 and the southern portion of the East Troublesome 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 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 4023 10593 4022 10587 4015 10589 4012 10593
      4012 10599 4012 10606 4017 10605 4024 10611
      4027 10611 4031 10608 4035 10610 4035 10609
      4035 10608 4033 10606 4033 10603 4028 10606
      4022 10602

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

$$

Hiris

451 
WGUS75 KBOU 230155
FFSBOU

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

COC049-230205-
/O.EXP.KBOU.FF.W.0036.000000T0000Z-210723T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
755 PM MDT Thu Jul 22 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 8 PM MDT THIS EVENING FOR 
NORTHEASTERN GRAND COUNTY...

The heavy rain threat has ended. Please continue to heed remaining 
road closures.

LAT...LON 4023 10593 4022 10587 4015 10589 4012 10593
      4012 10599 4012 10606 4017 10605 4024 10611
      4027 10611 4031 10608 4035 10610 4035 10609
      4035 10608 4033 10606 4033 10603 4028 10606
      4022 10602

$$

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, 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.