Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 6, NWS Denver/Boulder, CO

June 27, 2021Boulder County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jun 27, 2021, 5:56 PM MDT for Boulder County, Colorado. It was in force for 94 min. 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: Jun 27, 2021, 5:56 PM MDT (23:56 UTC)
Expired: Jun 27, 2021, 7:30 PM MDT
In force: 94 min
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Boulder County, CO

The radar

The Denver radar (KFTG), 78 km from the middle of the area, began a volume at 23:56 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
Jun 27, 6:18 PM MDT	FLASH FLOOD	5 Ene Jamestown, CO	LAW ENFORCEMENT IS REPORTING A 3-4 FOOT SURGE OF DEBRIS AND WATER FLOWING DOWN GEER CANYON.

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, 11.9 hours before the alert went out and 181 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: 7 J/kg
Mixed-layer CIN: -55 J/kg
Mixed-layer LCL: 1346 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 23 m²/s²
0-3 km storm-relative helicity: 3 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

535 
WGUS55 KBOU 272356
FFWBOU
COC013-280130-
/O.NEW.KBOU.FF.W.0006.210627T2356Z-210628T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
556 PM MDT Sun Jun 27 2021

The National Weather Service in Denver has issued a

* Flash Flood Warning for...
  North Central Boulder County in northeastern Colorado...

* Until 730 PM MDT.

* At 556 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 0.3 and 0.6 inches of 
  rain have fallen. 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...
  the Calwood Burn Area of North Central Boulder County

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Heavy rainfall will cause flash flooding of creeks, streams, and 
ditches in the Calwood burn area. Rock slides or debris flows can 
also be expected. The main areas of concern are Heil Valley Ranch 
and Lefthand Creek just above US 36.

&&

LAT...LON 4019 10536 4019 10531 4019 10530 4013 10527
      4012 10528 4012 10536

FLASH FLOOD...RADAR INDICATED

$$

Barjenbruch

3 follow-up statements

052 
WGUS75 KBOU 280033
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
633 PM MDT Sun Jun 27 2021

COC013-280130-
/O.CON.KBOU.FF.W.0006.000000T0000Z-210628T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boulder CO-
633 PM MDT Sun Jun 27 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 730 PM MDT THIS 
EVENING FOR NORTH CENTRAL BOULDER COUNTY...

At 633 PM MDT, local law enforcement reported flash flooding with a 
3 to 4 foot deep surge of debris and water flowing down Geer Canyon, 
which may impact stretches of Geer Canyon Drive.  Another 1 to 2 
foot surge was moving down Lefthand Creek.

HAZARD...Life threatening flash flooding.

SOURCE...Law enforcement reported.

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

Some locations that will experience flash flooding include...
  the Calwood Burn Area of North Central Boulder County

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Heavy rainfall will cause flash flooding of creeks, streams, and 
ditches in the Calwood burn area. Rock slides or debris flows can 
also be expected. The main areas of concern are Geer Canyon Drive, 
Heil Valley Ranch, and Lefthand Creek just above US 36.

&&

LAT...LON 4019 10536 4019 10531 4019 10530 4013 10527
      4012 10528 4012 10536

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

$$

Barjenbruch

234 
WGUS75 KBOU 280103
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
703 PM MDT Sun Jun 27 2021

COC013-280130-
/O.CON.KBOU.FF.W.0006.000000T0000Z-210628T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boulder CO-
703 PM MDT Sun Jun 27 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 730 PM MDT THIS 
EVENING FOR NORTH CENTRAL BOULDER COUNTY...

At 703 PM MDT, local law enforcement reported flash flooding and 
debris flows in the Calwood Burn Area are beginning to recede.

HAZARD...Flash flooding caused by heavy rain.

SOURCE...Law enforcement reported.

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...
  the Calwood Burn Area of North Central Boulder County

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Heavy rainfall has caused flash flooding of creeks, streams, and 
ditches in the Calwood burn area. Rock slides or debris flows can 
also be expected. The main areas of concern are Geer Canyon, Heil 
Valley Ranch, and Lefthand Creek just above US 36.

&&

LAT...LON 4019 10536 4019 10531 4019 10530 4013 10527
      4012 10528 4012 10536

FLASH FLOOD...OBSERVED

$$

Barjenbruch

656 
WGUS75 KBOU 280123
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
723 PM MDT Sun Jun 27 2021

COC013-280133-
/O.EXP.KBOU.FF.W.0006.000000T0000Z-210628T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boulder CO-
723 PM MDT Sun Jun 27 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 730 PM MDT THIS EVENING FOR 
NORTH CENTRAL BOULDER COUNTY...

Flood waters have receded. Flooding is no longer expected to pose a 
threat.

LAT...LON 4019 10536 4019 10531 4019 10530 4013 10527
      4012 10528 4012 10536

$$

Barjenbruch

The office that day

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

Issued	Product	Office	Counties	Lasted
Jun 27, 4:24 PM MDT	Special Weather Statement	BOU	Broomfield	36 min
Jun 27, 5:35 PM MDT	Areal Flood Advisory	BOU	Boulder	25 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.