Alert archive / Colorado / Flash Flood Warnings in 2021

Flash Flood Warning 59, NWS Denver/Boulder, CO

July 31, 2021Larimer County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at Jul 31, 2021, 3:24 PM MDT for Larimer County, Colorado. It was in force for 81 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 31, 2021, 3:24 PM MDT (21:24 UTC)
Expired
Jul 31, 2021, 4:45 PM MDT
In force
81 min
Issued by
NWS Denver/Boulder, CO
Area
Storm-based polygon
Damage threat
Considerable
Flood severity
None

County Larimer County, CO

The radar

The Cheyenne radar (KCYS), 87 km from the middle of the area, began a volume at 21:27 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, 9.4 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-pSkew-T log-p diagram, Denver, CO at 12:00Z on 2021-07-31Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 44 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Denver, CO at 12:00Z on 2021-07-31The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -71 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
44 J/kg
Mixed-layer CIN
-277 J/kg
Mixed-layer LCL
1127 m above ground
0-6 km bulk shear
13 kt
0-1 km storm-relative helicity
-71 m²/s²
0-3 km storm-relative helicity
-21 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

218 
WGUS55 KBOU 312124
FFWBOU
COC069-312245-
/O.NEW.KBOU.FF.W.0059.210731T2124Z-210731T2245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
324 PM MDT Sat Jul 31 2021

The National Weather Service in Denver has issued a

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

* Until 445 PM MDT.

* At 324 PM MDT, Emergency management reported thunderstorms 
  producing heavy rain across the warned area. Between 0.5 and 0.75 
  inches of rain has fallen. Additional rainfall amounts up to 0.50 
  inches are possible in the warned area. Flash flooding is already 
  occurring.

  HAZARD...Life threatening flash flooding. Thunderstorms
           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...
  mainly rural areas of Western Larimer County including the Black 
  Hollow Road area and drainage.

This includes the following streams and drainages...
  Cache La Poudre River and Dry Creek, Black Hollow

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

THIS IS A LIFE THREATENING SITUATION! Heavy Rainfall will cause 
extensive and severe flooding of creeks, streams, roads and culverts 
in the affected part of the Cameron Peak burn area. Rock slides or 
debris flows can also be expected across roads in the warning area.

&&

LAT...LON 4070 10568 4071 10562 4069 10559 4069 10569

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

$$

RPK
1 follow-up statement
111 
WGUS75 KBOU 312240
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
440 PM MDT Sat Jul 31 2021

COC069-312250-
/O.EXP.KBOU.FF.W.0059.000000T0000Z-210731T2245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Larimer CO-
440 PM MDT Sat Jul 31 2021

...FLASH FLOOD WARNING WILL EXPIRE AT 445 PM MDT THIS AFTERNOON FOR 
WESTERN LARIMER COUNTY...

Flood waters have receded. The heavy rain has ended. Flooding is no 
longer expected to pose a threat. Please continue to heed remaining 
road closures.

A Flash Flood Watch remains in effect until 900 PM MDT for Portions 
of central and north central Colorado.

LAT...LON 4070 10568 4071 10562 4069 10559 4069 10569

$$

RPK

The office that day

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

IssuedProductOfficeCountiesLasted
Jul 30, 6:01 PM MDTAreal Flood AdvisoryBOUBoulder, Broomfield, Weld59 min
Jul 30, 6:08 PM MDTAreal Flood AdvisoryBOUAdams, Denver82 min
Jul 30, 6:48 PM MDTAreal Flood AdvisoryBOUDouglas, Elbert117 min
Jul 30, 7:13 PM MDTAreal Flood WarningBOULarimer3 hr
Jul 30, 7:35 PM MDTAreal Flood AdvisoryBOUBoulder70 min
Jul 30, 7:52 PM MDTAreal Flood AdvisoryBOUBoulder, Broomfield, Weld83 min
Jul 30, 7:53 PM MDTAreal Flood AdvisoryBOULarimer68 min
Jul 30, 8:19 PM MDTAreal Flood AdvisoryBOUDouglas, Jefferson42 min
Jul 30, 9:34 PM MDTAreal Flood AdvisoryBOUAdams, Boulder, Broomfield, Denver, Jefferson, Weld56 min
Jul 30, 9:35 PM MDTAreal Flood AdvisoryBOUClear Creek, Gilpin3 hr
Jul 30, 10:18 PM MDTFlash Flood WarningBOUBoulder, Broomfield, Weld3 hr
Jul 30, 11:17 PM MDTSpecial Weather StatementBOUWeld28 min
Jul 30, 11:24 PM MDTAreal Flood AdvisoryBOUWeld81 min
Jul 30, 11:40 PM MDTAreal Flood AdvisoryBOUWeld60 min
Jul 31, 1:12 AM MDTSpecial Weather StatementBOULogan33 min
Jul 31, 2:39 AM MDTSpecial Weather StatementBOULogan51 min
Jul 31, 3:20 AM MDTSpecial Weather StatementBOUPhillips, Sedgwick40 min
Jul 31, 3:59 AM MDTAreal Flood AdvisoryBOULogan, Phillips, Sedgwick74 min
Jul 31, 11:49 AM MDTFlash Flood WarningBOULarimer2 hr
Jul 31, 12:27 PM MDTFlash Flood WarningBOUGrand3 hr
Jul 31, 12:29 PM MDTAreal Flood AdvisoryBOUGrand91 min
Jul 31, 12:32 PM MDTAreal Flood AdvisoryBOUGrand88 min
Jul 31, 12:34 PM MDTAreal Flood AdvisoryBOUGrand86 min
Jul 31, 12:39 PM MDTAreal Flood AdvisoryBOUPark81 min
Jul 31, 12:42 PM MDTAreal Flood AdvisoryBOUPark93 min
Jul 31, 1:05 PM MDTAreal Flood AdvisoryBOULarimer85 min
Jul 31, 1:33 PM MDTAreal Flood AdvisoryBOUGrand87 min
Jul 31, 2:16 PM MDTFlash Flood WarningBOULarimer89 min
Jul 31, 2:43 PM MDTFlash Flood WarningBOULarimer92 min
Jul 31, 2:57 PM MDTAreal Flood AdvisoryBOUPark93 min
Jul 31, 3:29 PM MDTAreal Flood AdvisoryBOUBoulder91 min
Jul 31, 3:33 PM MDTFlash Flood WarningBOUPark3 hr
Jul 31, 3:37 PM MDTFlash Flood WarningBOUBoulder3 hr
Jul 31, 3:51 PM MDTAreal Flood AdvisoryBOUBoulder84 min
Jul 31, 4:31 PM MDTAreal Flood AdvisoryBOUPark89 min
Jul 31, 4:42 PM MDTAreal Flood AdvisoryBOUPark93 min
Jul 31, 4:52 PM MDTAreal Flood AdvisoryBOUPark83 min

Nearby

Flash Flood Warnings in Colorado, 2021Every 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.