Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 35, NWS Denver/Boulder, CO

July 21, 2021Douglas County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 21, 2021, 6:19 PM MDT for Douglas 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, 6:19 PM MDT (00:19 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 Douglas County, CO

The radar

The Denver radar (KFTG), 56 km from the middle of the area, began a volume at 00:22 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 00:00Z, 0.3 hours before the alert went out and 143 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: 273 J/kg
Mixed-layer CIN: -59 J/kg
Mixed-layer LCL: 2525 m above ground
0-6 km bulk shear: 10 kt
0-1 km storm-relative helicity: 21 m²/s²
0-3 km storm-relative helicity: 99 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

024 
WGUS55 KBOU 220019
FFWBOU
COC035-220315-
/O.NEW.KBOU.FF.W.0035.210722T0019Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in Denver has issued a

* Flash Flood Warning for...
  Southeastern Douglas County in northeastern Colorado...

* Until 915 PM MDT.

* At 619 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 2 and 3 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...
  Franktown, The Pinery and Castlewood Canyon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3944 10478 3944 10476 3935 10474 3930 10466
      3925 10466 3917 10466 3916 10466 3918 10478
      3930 10478

FLASH FLOOD...RADAR INDICATED

$$

TH

4 follow-up statements

129 
WGUS75 KBOU 220130
FFSBOU

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

COC035-220315-
/O.CON.KBOU.FF.W.0035.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Douglas CO-
730 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 915 PM MDT THIS 
EVENING FOR SOUTHEASTERN DOUGLAS COUNTY...

At 730 PM MDT, Doppler radar and automated rain gages indicate 
between 2 and 5 inches of rain have fallen in the past 1.5 hours in 
Antelope Creek and upper Cherry Creek drainages. Thunderstorms 
continue, but the rainfall intensity has decreased, with light to 
moderate rainfall continuing. Flooding is ongoing or expected to 
begin shortly not only in southeast Douglas County, but also in and 
downstream on Cherry Creek in west central Douglas County.

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...
Castlewood Canyon and Franktown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3944 10478 3944 10476 3935 10474 3930 10466
      3925 10466 3917 10466 3916 10466 3918 10478
      3930 10478

FLASH FLOOD...RADAR INDICATED

$$

TH

178 
WGUS75 KBOU 220135
FFSBOU

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

COC035-220315-
/O.CON.KBOU.FF.W.0035.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Douglas CO-
735 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 915 PM MDT THIS 
EVENING FOR SOUTHEASTERN DOUGLAS COUNTY...

At 735 PM MDT, At 730 PM MDT...Doppler radar and automated rain 
gages indicate between 2 and 5 inches of rain have fallen in the 
past 1.5 hours in the Antelope creek and upper Cherry Creek 
drainages. Thunderstorms with light to moderate rain continue, with 
the rainfall intensity decreasing. Flooding is ongoing or expected 
to begin shortly not only in southeast Douglas County, but also in 
and downstream on Cherry Creek in east central Douglas County.

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...
  Northeastern Castle Rock, Franktown, The Pinery and Castlewood 
  Canyon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3944 10478 3944 10476 3935 10474 3930 10466
      3925 10466 3917 10466 3916 10466 3918 10478
      3930 10478

FLASH FLOOD...RADAR INDICATED

$$

TH

607 
WGUS75 KBOU 220137 CCA
FFSBOU

Flash Flood Statement...CORRECTED
National Weather Service Denver CO
737 PM MDT Wed Jul 21 2021

COC035-220315-
/O.COR.KBOU.FF.W.0035.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Douglas CO-
737 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 915 PM MDT THIS 
EVENING FOR SOUTHEASTERN DOUGLAS COUNTY...

At 735 PM MDT, Doppler radar and automated rain gages indicate 
between 2 and 5 inches of rain have fallen in the past 1.5 hours in 
the Antelope creek and upper Cherry Creek drainages. Thunderstorms 
with light to moderate rain continue, with the rainfall intensity 
decreasing. Flooding is ongoing or expected to begin shortly not 
only in southeast Douglas County, but also in and downstream on 
Cherry Creek in east central Douglas County.

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...
Castlewood Canyon and Franktown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3944 10478 3944 10476 3935 10474 3930 10466
      3925 10466 3917 10466 3916 10466 3918 10478
      3930 10478

FLASH FLOOD...RADAR INDICATED

$$

TH

043 
WGUS75 KBOU 220314
FFSBOU

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

COC035-220324-
/O.EXP.KBOU.FF.W.0035.000000T0000Z-210722T0315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Douglas CO-
914 PM MDT Wed Jul 21 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 915 PM MDT THIS EVENING FOR 
SOUTHEASTERN DOUGLAS COUNTY...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures. Light rain 
showers are expected to continue this evening.

LAT...LON 3944 10478 3944 10476 3935 10474 3930 10466
      3925 10466 3917 10466 3916 10466 3918 10478
      3930 10478

$$

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, 6:11 PM MDT	Flash Flood Warning	BOU	Grand	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.