Flash Flooding and Hail in Colorado, August 31, 2001

Name: Flash Flooding and Hail in Colorado, August 31, 2001
Start: 2001-08-31T12:50
End: 2001-08-31T17:00
Location: Colorado

August 31, 2001 · NWS BOU · 4 events in 2 counties and zones

2 hail, 2 flash flood, as filed by the National Weather Service.

Where it happened

Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 4

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Denver/Boulder, CO wrote its last area forecast discussion before the first event at Aug 31, 1:35 AM MST, 11 hours 15 minutes earlier.

Area forecast discussion, Aug 31, 1:35 AM MST, 11 hours 15 minutes before

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
235 AM MDT FRI AUG 31 2001

FLAT UPR LVL RDG WL GRADUALLY REBUILD ITSELF OVR AREA BY THE WEEKEND
HOWEVER FOR TODAY ANOTHER WK DISTURBANCE IS FCST TO MOVE ACRS NRN CO
BY AFTN.  THIS FEATURE DOES HAVE SOME WK QG ASCENT AND POTENTIAL
VORTICITY AT 300 MB IN GRIDDED DATA SO MAY SEE A LITTLE BETTER
COVERAGE OF TSTMS THIS AFTN AS COMPARED TO YESTERDAY.  WOULD EXPECT
MOST ACTIVITY TO DVLP OVR THE MTNS AND FOOTHILLS INITIALLY WITH
OUTFLOW BOUNDARIES GENERATING ADDITIONAL DEVELOPMENT OVR THE NERN
PLAINS BY LATE AFTN INTO THE EVENING HRS.  BOTH MESO-ETA AND NGM
SHOW FAIRLY STG SE LOW LVL JET DVLPG THIS EVENING OVR NERN PLAINS
WHICH MAY KEEP CONVECTION GOING OVERNIGHT AS SOME TYPE OF MCS
DVLPS.  TEMPS TODAY SHOULD BE ABOUT THE SAME AS YESTERDAY BASED ON
LITTLE CHG IN LOW LVL TEMP FIELDS.

ON SAT UPR LVL RDG WL BEGIN TO SLOWLY BUILD ACRS RGN HOWEVER
LINGERING MID LVL MSTR AND FAIRLY STEEP LAPSE RATES SHOULD ALLOW FOR
SOME AFTN TSTMS IN THE MTNS AND FOOTHILLS.  OVR NERN CO LOW LVL FLOW
IS FCST TO BECOME MORE NWLY WITH SOME DRYING OCCURRING SO TSTM
COVERAGE SHOULD BE LESS THAN TODAY.  TEMPS SHOULD BE WARMER ON SAT
AS 700 MB READINGS RISE FROM 2 TO 3 DEGREES.  CANT FIGURE OUT TEMP
GUIDANCE FROM NGM AND MAV WHICH ACTUALLY SHOW TEMPS COOLER THAN
TODAY WHICH DOESNT MAKE MUCH SENSE BASED ON THEIR 700 MB TEMP
FIELDS SO WL GO ABV GUIDANCE.

IN THE EXTENDED PD UPR LVL RDG WL CONT OVR RGN THRU EARLY NEXT WK
WITH MID LVL FLOW BECOMING MORE S TO SW.  TEMPS SHOULD CONT TO BE
ABV NORMAL THRU THE PD.  WITH S TO SW MID LVL FLOW DVLPG MAY CONT TO
SEE SOME MONSOON MSTR OVR THE AREA WITH SOME AFTN AND EVENING TSTMS
MAINLY IN THE MTNS AND FOOTHILLS.   KLEYLA

.DEN...NONE.

In the hours before

Special weather statement, Aug 31, 9:41 AM MST, 3 hours 9 minutes before

COZ030>051-312000-

HAZARDOUS WEATHER OUTLOOK FOR NORTHEAST AND NORTH CENTRAL COLORADO
NATIONAL WEATHER SERVICE DENVER CO
1040 AM MDT THU AUG 30 2001

THIS OUTLOOK PERTAINS TO THE FOLLOWING COLORADO COUNTIES

ADAMS     ARAPAHOE     BOULDER   CLEAR CREEK   DENVER       DOUGLAS
ELBERT    GILPIN       GRAND     JACKSON       JEFFERSON    LARIMER
LINCOLN   LOGAN        MORGAN    PARK          PHILLIPS     SEDGWICK
SUMMIT    WASHINGTON   WELD

SYNOPSIS:  A WEAK UPPER LEVEL TROUGH AND LOW LEVEL MOISTURE ON THE
PLAINS WILL PRODUCE INCREASED THUNDERSTORM ACTIVITY TODAY.
SCATTERED STORMS WILL DEVELOP OVER THE MOUNTAINS EARLY THIS
AFTERNOON...BUT CLOUD COVER WILL DELAY THUNDERSTORM DEVELOPMENT ON
THE PLAINS UNTIL LATE IN THE DAY.  STORMS SHOULD BE MOST NUMEROUS ON
THE PLAINS THIS EVENING...AND MAY CONTINUE INTO THE EARLY MORNING
HOURS NEAR THE EASTERN BORDER.

A WIND CONVERGENCE ZONE IS EXPECTED TO DEVELOP TO THE SOUTH AND
EAST OF DENVER THIS AFTERNOON.  THIS WILL BE A LIKELY PLACE FOR
THUNDERSTORM INITIATION.  THE STORMS SHOULD BE MOST NUMEROUS EAST OF
A LINE FROM NEW RAYMER THROUGH BENNETT TO CASTLE ROCK...WHERE THERE
IS THE BEST MOISTURE.  SOME OF THE STORMS WILL BE MARGINALLY
SEVERE...WITH HAIL UP TO AN INCH IN DIAMETER...WIND GUSTS TO 60
MPH...AND UP TO AN 1.5 INCHES OF RAIN IN AN HOUR.

SPOTTER ACTIVATION MAY BE NEEDED AFTER 3 PM.

OUTLOOK FOR SATURDAY:  WARMER WITH ISOLATED AFTERNOON AND EVENING
THUNDERSTORMS.

GIMMESTAD

Special weather statement, Aug 31, 12:45 PM MST, 5 minutes before

COZ030>051-312200-

HAZARDOUS WEATHER OUTLOOK FOR NORTHEAST AND NORTH CENTRAL COLORADO
NATIONAL WEATHER SERVICE DENVER CO
145 PM MDT FRI AUG 31 2001

THIS OUTLOOK PERTAINS TO THE FOLLOWING COLORADO COUNTIES

ADAMS     ARAPAHOE     BOULDER   CLEAR CREEK   DENVER       DOUGLAS
ELBERT    GILPIN       GRAND     JACKSON       JEFFERSON    LARIMER
LINCOLN   LOGAN        MORGAN    PARK          PHILLIPS     SEDGWICK
SUMMIT    WASHINGTON   WELD

SYNOPSIS:  THUNDERSTORMS WILL CONTINUE OVER THE MOUNTAINS THROUGH
THIS EVENING...AND WILL BECOME MORE NUMEROUS OVER THE PLAINS.
STORMS MAY CONTINUE INTO THE EARLY MORNING HOURS NEAR THE EASTERN
BORDER.

A WIND CONVERGENCE ZONE FROM DOUGLAS COUNTY TO NEAR AKRON AND
STERLING WILL CONTINUE TO BE THE FOCUS FOR THUNDERSTORM ACTIVITY.
THIS LINE IS EXPECTED TO DRIFT SLOWLY EAST DURING THE NIGHT.  SOME
OF THE STORMS ALONG AND EAST OF THIS LINE WILL BE MARGINALLY
SEVERE...WITH HAIL UP TO AN INCH IN DIAMETER...WIND GUSTS TO 60
MPH...AND UP TO 1.5 INCHES OF RAIN IN AN HOUR.  DUE TO THE SLOW
MOVEMENT OF THIS LINE...FLOODING MAY BE POSSIBLE IN AREAS WHERE
STORMS REPEATEDLY CROSS THE SAME AREA.

DUE TO THE LOW THREAT OF SEVERE WEATHER NEAR THE FRONT
RANGE...SPOTTER ACTIVATION IS NOT EXPECTED TODAY.

OUTLOOK FOR SATURDAY:  WARMER WITH ISOLATED AFTERNOON AND EVENING
THUNDERSTORMS.

GIMMESTAD

The radar

The Denver radar (KFTG), 38 km away, was scanning. The volume nearest the first event began at 19:48 UTC.

Open the radar archive at this moment

Event by event

2 hail, 2 flash flood. Local standard time, as filed.

Hail, Elbert

When: August 31, 12:50 PM MST
Where: Elbert County, 10 mi NE of Elizabeth
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 39.450, -104.467

Hail, Washington

When: August 31, 1:40 PM MST
Where: Washington County, 17 mi N of Last Chance
Measured: 1 in hail
Reported by: TRAINED SPOTTER
Coordinates: 39.983, -103.583

Flash Flood, Washington

When: August 31, 2:15 PM MST to 5:00 PM MST
Where: Washington County, West Central Portion
Reported by: GENERAL PUBLIC
Coordinates: 39.971, -103.201 (the zone’s center; the record gives no point)

Flash Flood, Washington

When: August 31, 2:51 PM MST to 5:00 PM MST
Where: Washington County, Southwest Portion
Reported by: GENERAL PUBLIC
Coordinates: 39.971, -103.201 (the zone’s center; the record gives no point)

Thunderstorms producing very heavy rain caused flooding and flash flooding problems over portions of Washington County. Doppler radar estimates ranged from 3 to 6 inches across the area. Approximately 200 acres of sidehill grass washed downhill, covering a hay field. Dry Creek flooded low lying pastures and fields about 10 miles southwest of Akron. Another creek jumped its banks and flooded some county roads 6 miles south of Woodrow.

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Colorado in 2001 Every state in 2001 This day in weather history Warnings in Colorado, August 2001

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 5265106, 5265107, 5265108, 5265109.