Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 27, NWS Denver/Boulder, CO

July 20, 2021Larimer County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 20, 2021, 5:24 PM MDT for Larimer County, Colorado. It was in force for 51 min. 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 20, 2021, 5:24 PM MDT (23:24 UTC)
Expired: Jul 20, 2021, 6:15 PM MDT
In force: 51 min
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Larimer County, CO

The radar

The Cheyenne radar (KCYS), 89 km from the middle of the area, began a volume at 23:26 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, 11.4 hours before the alert went out and 225 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: 2720 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: -20 m²/s²
0-3 km storm-relative helicity: 70 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

135 
WGUS55 KBOU 202324
FFWBOU
COC069-210015-
/O.NEW.KBOU.FF.W.0027.210720T2324Z-210721T0015Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
524 PM MDT Tue Jul 20 2021

The National Weather Service in Denver has issued a

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

* Until 615 PM MDT.

* At 524 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the Cameron Peak burn area. Between 0.5 and 1 
  inch of rain has fallen. The expected rainfall rate is 1 to 2 
  inches in 1 hour. Additional rainfall amounts of 0.5 to 1 inch are 
  possible in the warned area. 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...
  Rustic and Kinikinik.

This includes the following additional locations...
Jacks Gulch, Lower Pingree Park Road, Gulches along Highway 14 near 
and above Rustic, Rising water and large debris in the Poudre River, 
Pingree Hill, Crown Point Road and Remote areas in the Cameron Peak 
Wilderness.

This includes the following streams and drainages...
  Bennett Creek, Little Beaver Creek, Sheep Creek, Cache La Poudre 
  River, Dry Creek, Peterson Creek, Roaring Creek and South Fork 
  Cache La Poudre River.

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.

Heavy Rainfall will cause flash flooding of small creeks, streams, 
and ditches in the affected part of the Cameron Peak burn area. Rock 
slides or debris flows can also be expected across rural roads.

&&

LAT...LON 4067 10581 4075 10574 4071 10555 4067 10551
      4064 10549 4060 10571

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL...1-2 INCHES IN 1 HOUR

$$

Direnzo

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 20, 3:27 PM MDT	Areal Flood Advisory	BOU	Grand	78 min
Jul 20, 4:29 PM MDT	Areal Flood Advisory	BOU	Larimer	91 min
Jul 20, 4:53 PM MDT	Flash Flood Warning	BOU	Larimer	82 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.