Colorado, 1999

Flash Flood and Flooding in Colorado, August 4, 1999

August 4, 1999 · NWS BOU · 5 events in 5 counties and zones

5 inches of rainfall in approximately 3 hours. Near the junction of Interstate 25 and State Highway 36, up to 4 feet of water flooded an auto dealership.

Where it happened

Every event with a place to put it; 5 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

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The toll

Deaths
0
Injuries
0
Property damage
$500,000
Crop damage
None recorded
Events
5

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 happened

The episode as NWS BOU wrote it up.

Flooding and flash flooding problems developed over portions of the Urban Corridor as slow moving thunderstorms dumped anywhere from 2 to 3.5 inches of rainfall in approximately 3 hours. Near the junction of Interstate 25 and State Highway 36, up to 4 feet of water flooded an auto dealership. Approximately 45 cars were ruined. Sections of Interstate 25 and State Highway 36 near the interchange were closed due to floodwaters. Damage estimates to the dealership alone were approximately $500,000. Floodwaters, up to 5 feet deep, forced the evacuation of two mobile home parks in Federal Heights. In addition, railroad tracks were washed out near Federal Blvd. and 64th Avenue.Numerous outages were reported with widespread blackouts in Thornton and Littleton. Along Massey Draw, near Carr Street and Chatfield Reservoir, four homes were flood damaged and portions of their backyards washed out. Widespread street flooding was also reported at Boulder, Fort Collins and Greeley. Several buildings were flood damaged in Fort Collins as well as at the CU Memorial Center in Boulder.

The radar

The Denver radar (KFTG), 64 km away, was scanning. The volume nearest the first event began at 20:59 UTC.

Open the radar archive at this moment

Event by event

4 flood, 1 flash flood. Local standard time, as filed.

Flood, Jefferson

When
August 4, 2:00 PM MST to 5:00 PM MST
Where
Jefferson County, Countywide
Reported by
NEWSPAPER
Coordinates
39.586, -105.250 (the zone’s center; the record gives no point)

Flood, Boulder

When
August 4, 2:00 PM MST to 5:00 PM MST
Where
Boulder County, Boulder
Reported by
NEWSPAPER
Coordinates
40.093, -105.358 (the zone’s center; the record gives no point)

Flood, Larimer

When
August 4, 2:00 PM MST to 5:00 PM MST
Where
Larimer County, Ft Collins
Reported by
NEWSPAPER
Coordinates
40.666, -105.461 (the zone’s center; the record gives no point)

Flash Flood, Adams

When
August 4, 2:00 PM MST to 5:00 PM MST
Where
Adams County, West Portion
Property damage
$500,000
Reported by
NEWSPAPER
Coordinates
39.874, -104.338 (the zone’s center; the record gives no point)

Flood, Arapahoe

When
August 4, 2:00 PM MST
Where
Arapahoe County, Littleton
Reported by
NEWSPAPER
Coordinates
39.650, -104.339 (the zone’s center; the record gives no point)

What these are

Flood
Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
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 1999Every state in 1999This day in weather historyWarnings in Colorado, August 1999

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: 5718449, 5718450, 5718451, 5718452, 5718453.