Colorado, 2002

Flash Flooding and Hail in Colorado, July 21, 2002

July 21, 2002 · NWS BOU · 4 events in 3 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 Jul 21, 2:30 PM MST, 1 hour 29 minutes earlier.

Area forecast discussion, Jul 21, 2:30 PM MST, 1 hour 29 minutes before
NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
330 PM MDT SUN JUL 21 2002

DISCUSSION:  ONE SHORT WAVE MOVED OUT ACRS THE NERN CO PLAINS ARND
SUNRISE THIS MRNG WITH A BAND OF SHOWERS.  A SECOND...WEAKER WAVE IS
MOVING OUT OF THE NRN MTNS THIS AFTN.  THE SUBSIDENCE BEHIND THE
FIRST SHORT WAVE HAS SUPPRESSED AFTN CONVECTIVE ACTIVITY ACRS MOST
OF THE FCST AREA.  HOWEVER...SOME SHOWERS ARE MOVING ACRS LARIMER
AND WELD COUNTIES IN ASSOCIATION WITH THE SECOND WAVE.  NELY WINDS
ACRS THE PLAINS ARE COMBINING WITH HIGHER DEWPTS TO KEEP AFTN TEMPS
ON THE PLAINS BELOW CONVECTIVE TEMPS.  WINDS ALOFT ARE ALSO WEAK
WHICH WL KEEP SHOWERS FROM BECMG TOO ORGANIZED.  AS THE SUN GOES
DOWN...SHOWERS SHOULD DISSIPATE.  MODELS APPEAR TO BE OVERDOING THE
PCPN FOR THIS EVENING...SINCE THE SUBSIDENCE IS KEEPING MOST OF THE
MID-AFTN CONVECTION CAPPED.  THE ELY/NELY WINDS CONTG OVERNIGHT
ALONG WITH OUTFLOW FM CONVECTION IN THE NEBRASKA PNHNDL WL PROBABLY
PRODUCE AREAS OF STRATUS ON THE PLAINS AFTER MIDNIGHT.

OVER THE NEXT COUPLE DAYS ANOTHER STRONG UPR LVL RIDGE WL DVLP OVR
THE 4-CRNRS AND SWRN U.S.  HOWEVER...MODELS ARE ALSO INDICATING
HIGHER SPECIFIC HUMIDITY VALUES AT MID LEVELS THAN WE HAVE SEEN UP
TO THIS POINT IN THE SUMMER.  IF THE UPR RIDGE ACTUALLY EVOLVES WITH
THE MID LVL MSTR PRESENT...IT WILL LINGER OVR THE REGION WITH THE
MORE CLIMATOLOGICALLY FAVORED AFTN/EVE SHOWER PATTERN.  SATELLITE
PICTURES HAVE BEEN SHOWING GOOD SHOWER DVLPMNT OVR THE MTNS FOR THE
PAST SEVERAL DAYS...SO IT IS APPARENT THAT THE MONSOON IS
ESTABLISHING ITSELF.  AS LONG AS THE UPR RDG HANGS ARND WITH THE
MID-LVL MSTR PRESENT...THE CYCLE OF MRNG SUN AND AFTN/EVE SHOWERS
WILL CONT.  SINCE THE FLOW PATTERN ALOFT WILL BE WEAK...WL LIMIT THE
MENTION OF SHOWER ACTIVITY TO THE MTNS AND ADJACENT PLAINS.  FCSTG
ANY PCPN ON THE PLAINS WILL HAVE TO WAIT FOR SHORTER FCST PERIODS
WHEN IT WL BE PSBL TO ANALYZE POOLING OF LOW LVL MSTR AND PSBL BNDRY
INTERACTIONS.                                                  KDRBY

.DEN...NONE.

The radar

The Denver radar (KFTG), 24 km away, was scanning. The volume nearest the first event began at 22:57 UTC.

Open the radar archive at this moment

Event by event

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

Hail, Adams

When
July 21, 3:59 PM MST
Where
Adams County, 14 mi NNE of Bennett
Measured
0.75 in hail
Reported by
TRAINED SPOTTER
Coordinates
39.933, -104.333

Hail, Adams

When
July 21, 4:59 PM MST
Where
Adams County, 11 mi NNE of Bennett
Measured
0.75 in hail
Reported by
TRAINED SPOTTER
Coordinates
39.900, -104.350

Flash Flood, Jefferson

When
July 21, 8:00 PM MST to 9:45 PM MST
Where
Jefferson County, South Portion
Reported by
LAW ENFORCEMENT
Coordinates
39.586, -105.250 (the zone’s center; the record gives no point)

Flash Flood, Douglas

When
July 21, 8:00 PM MST to 9:45 PM MST
Where
Douglas County, West Portion
Reported by
LAW ENFORCEMENT
Coordinates
39.330, -104.930 (the zone’s center; the record gives no point)

Heavy rain caused flash flooding problems in the Hayman burn area. South Deckers Road, State Highway 126, had to be closed as 4 feet of water inundated a section of the roadway. The forest service had to remove 40 truck loads of sediment from the area. Also, in southwest Douglas County, a secondary service road was washed out by heavy debris flow.

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

More

Every storm in Colorado in 2002Every state in 2002This day in weather historyWarnings in Colorado, July 2002

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: 5310047, 5310050, 5310048, 5310049.