Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 33, NWS Denver/Boulder, CO

July 21, 2021Clear Creek County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 21, 2021, 5:06 PM MDT for Clear Creek 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, 5:06 PM MDT (23:06 UTC)
Expired: Jul 21, 2021, 8:15 PM MDT
In force: 3 hr
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Clear Creek County, CO

The radar

The Denver radar (KFTG), 77 km from the middle of the area, began a volume at 23:06 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

Denver, CO (KDNR), launched 12:00Z, 11.1 hours before the alert went out and 189 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: 2182 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: -4 m²/s²
0-3 km storm-relative helicity: 13 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

881 
WGUS55 KBOU 212306
FFWBOU
COC019-220215-
/O.NEW.KBOU.FF.W.0033.210721T2306Z-210722T0215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Denver has issued a

* Flash Flood Warning for...
  East Central Clear Creek County in central Colorado...

* Until 815 PM MDT.

* At 506 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Radar indicated that between 1 
  and 2 inches of rain have fallen in about 40 minutes. 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...
  Idaho Springs, Blue Valley and Floyd Hill.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Flooding is occurring or is imminent. It is important to know where 
you are relative to streams, rivers, or creeks which can become 
killers in heavy rains. Campers and hikers should avoid streams or 
creeks.

Excessive runoff from this storm will cause flash flooding of creeks 
and streams, roads and roadside culverts. The heavy rains could also 
trigger rock slides or debris flows in steep terrain.

&&

LAT...LON 3970 10540 3968 10546 3972 10553 3976 10548
      3976 10547 3976 10545 3975 10545 3976 10544
      3976 10543 3976 10542 3975 10542 3975 10541
      3975 10540

FLASH FLOOD...RADAR INDICATED

$$

RJK

2 follow-up statements

881 
WGUS75 KBOU 220026
FFSBOU

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

COC019-220215-
/O.CON.KBOU.FF.W.0033.000000T0000Z-210722T0215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Clear Creek CO-
626 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 815 PM MDT THIS 
EVENING FOR EAST CENTRAL CLEAR CREEK COUNTY...

At 626 PM MDT, Doppler radar indicated light rain continuing over 
0northestern Clear Creek County. Between 1.0 and 3.0 inches of rain 
have fallen in the warning area. Flash flooding is ongoing or 
expected to begin shortly. A rain gage at Clear Creek right by I-70 
measured 2.62 with this storm.

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...
  Idaho Springs, Blue Valley and Floyd Hill.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Flooding is occurring or is imminent. It is important to know where 
you are relative to streams, rivers, or creeks which can become 
killers in heavy rains. Campers and hikers should avoid streams or 
creeks.

Excessive runoff from this storm will cause flash flooding of creeks 
and streams, roads and roadside culverts. The heavy rains could also 
trigger rock slides or debris flows in steep terrain.

&&

LAT...LON 3970 10540 3968 10546 3972 10553 3976 10548
      3976 10547 3976 10545 3975 10545 3976 10544
      3976 10543 3976 10542 3975 10542 3975 10541
      3975 10540

FLASH FLOOD...RADAR INDICATED

$$

RJK

042 
WGUS75 KBOU 220209
FFSBOU

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

COC019-220219-
/O.EXP.KBOU.FF.W.0033.000000T0000Z-210722T0215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Clear Creek CO-
809 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 815 PM MDT THIS EVENING FOR 
EAST CENTRAL CLEAR CREEK COUNTY...

although weaker thunderstorms will persist this evening, the threat 
heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures.

LAT...LON 3970 10540 3968 10546 3972 10553 3976 10548
      3976 10547 3976 10545 3975 10545 3976 10544
      3976 10543 3976 10542 3975 10542 3975 10541
      3975 10540

$$

Cooper

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 20, 6:58 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Larimer	92 min
Jul 20, 7:09 PM MDT	Flash Flood Warning Considerable damage threat	BOU	Larimer	81 min
Jul 21, 3:18 AM MDT	Flash Flood Watch	BOU	Boulder, Grand, Jackson, Larimer	17 hr
Jul 21, 1:30 PM MDT	Flash Flood Warning	BOU	Larimer	3 hr
Jul 21, 1:56 PM MDT	Areal Flood Advisory	BOU	Grand	3 hr
Jul 21, 2:31 PM MDT	Areal Flood Advisory	BOU	Park	119 min
Jul 21, 2:44 PM MDT	Special Weather Statement	BOU	Teller	46 min
Jul 21, 2:47 PM MDT	Flash Flood Warning	BOU	Larimer	103 min
Jul 21, 3:16 PM MDT	Flash Flood Warning	BOU	Grand, Larimer	3 hr
Jul 21, 3:22 PM MDT	Areal Flood Advisory	BOU	Park	69 min
Jul 21, 4:40 PM MDT	Areal Flood Advisory	BOU	Douglas	65 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.