A deadly debris flow from the Cameron Peak burn area, struck Black Hollow Gulch west of Rustic on CO-14. The debris flow, estimated to be 5 to 8 feet deep, destroyed 6 homes and other structures.
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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.
The episode as NWS BOU wrote it up.
A deadly debris flow from the Cameron Peak burn area, struck Black Hollow Gulch west of Rustic on CO-14. The debris flow, estimated to be 5 to 8 feet deep, destroyed 6 homes and other structures. Four people were killed when their residence was swept away by the floodwaters. The houses and structures were at the mouth of Black Hollow Canyon on the Poudre River. The debris consisting of small, medium, and large boulders, mud, and entire burned trees flowed down the canyon and destroyed the houses in that area, including the bridge that crossed the Poudre River.
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 20, 1:59 PM MST, 2 hours 31 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 259 PM MDT Tue Jul 20 2021 .SHORT TERM...(This evening through Wednesday) Issued at 229 PM MDT Tue Jul 20 2021 At least a few showers and thunderstorms will continue this evening across the higher terrain, where a fairly robust monsoonal moisture surge has increased precipitable water amounts to above normal values. The bulk of this moisture is still west of our area, but our mountain do have enough moisture to work with for a few storms to produce brief heavy rain before instability decreases this evening. Upper level ridge will continue to spin over Colorado tonight and tomorrow and will gradually weaken/flatten by tomorrow afternoon. As a result, the flow turns a bit more west/southwesterly and the eastward edge of the moisture plume should spread into the northeast plains. PWATs tomorrow will be 0.75-1.05" across the high terrain, and generally 1.1-1.4 inches for the plains. Models show meager instability across the area, but very slow storm motions and high water values will bring some needed rain to the western half of the state, with storms potential pushing into the plains during the evening. Of course, this will also cause some hydro concerns... as noted in the Hydrology section below. Temperatures won't be dramatically different than today with highs again in the 90s for the plains. .LONG TERM...(Wednesday night through Tuesday) Issued at 229 PM MDT Tue Jul 20 2021 Upper level high pressure centered over the Four Corners Region through Thursday will flatten and elongate Friday into the weekend as a potent easterly wave retrogrades westward across the Desert Southwest. The presence of monsoonal moisture combined with daytime heating will result in a good chance for afternoon and evening showers and storms across the high country each day with only a stray shower or storm possible on the adjacent plains. With the slow movement of the storms that form and localized heavy rain possible, there will be a threat for flash flooding in the burn areas but at this time the risk is low. The Front Range Urban Corridor may see cooler temperatures along with a better chance for showers and storms on Saturday as a weak cold front moves across northeastern Colorado. By early next week, the models are showing the upper high shifting eastward into the Southern Plains States. This would be more of a classic monsoonal pattern which would continue the flow of subtropical moisture out of the Desert Southwest into Colorado. With PW's remaining at above normal values, locally heavy rainfall will still be a possibility each day. The models have been advertising this shift for the past couple of weeks, however the upper high has been very stubborn and has remained camped out over the Western U.S. If the upper high can shift far enough east, the northeastern plains would see a better chance for precipitation. Time will tell. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 229 PM MDT Tue Jul 20 2021 VFR conditions are likely through the TAF period. Smoke should continue to decrease through tomorrow, though slant vis reductions are still possible at times, especially this evening. Southeast winds will shift back closer to southerly drainage flow overnight. Overnight winds will be fairly strong, with 25kt gusts possible for several hours. Winds will weaken by daybreak tomorrow with light northeasterlies in the afternoon. Scattered showers/storms are possible after 18z tomorrow, with the best chances coming near 00z. Variable/gusty winds will be possible near storms. && .HYDROLOGY... Issued at 229 PM MDT Tue Jul 20 2021 Flash flooding risk will increase on Wednesday with the combination of increased moisture, slow storm motions, and long/skinny CAPE profiles. CAPE is still fairly meager across the area, but showers/storms during the afternoon will certainly pose a burn area flash flood risk, depending on where storm development is. 6HR HREF probability-matched mean QPF values do exceed 1" of liquid in some areas across the Front Range/Rabbit Ears Range, though there is obviously a great deal of uncertainty where the heaviest rain will fall. Across the rest of the forecast area, rainfall potential is low enough to avoid flash flooding, though low-lying/urban areas could see some water issues if storms make it into the plains. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && SHORT TERM...Hiris LONG TERM...Kalina AVIATION...Hiris HYDROLOGY...Hiris/Kalina
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1034 AM MDT Tue Jul 20 2021 COZ030>051-211645- Jackson County Below 9000 Feet- West Jackson and West Grand Counties Above 9000 Feet- Grand and Summit Counties Below 9000 Feet- South and East Jackson/Larimer/North and Northeast Grand/ Northwest Boulder Counties Above 9000 Feet- South and Southeast Grand/West Central and Southwest Boulder/ Gilpin/Clear Creek/Summit/North and West Park Counties Above 9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet- Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear Creek/Northeast Park Counties Below 9000 Feet- Central and Southeast Park County- Larimer County Below 6000 Feet/Northwest Weld County- Boulder And Jefferson Counties Below 6000 Feet/West Broomfield County- North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe Counties/East Broomfield County- Elbert/Central and East Douglas Counties Above 6000 Feet- Northeast Weld County-Central and South Weld County-Morgan County- Central and East Adams and Arapahoe Counties- North and Northeast Elbert County Below 6000 Feet/North Lincoln County- Southeast Elbert County Below 6000 Feet/South Lincoln County- Logan County-Washington County-Sedgwick County-Phillips County- 1034 AM MDT Tue Jul 20 2021 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight There will be scattered showers and thunderstorms over the higher terrain this afternoon and evening. A few of the storms could produce heavy rain with a limited threat of flash flooding over the burn scars. Over the plains it will be dry with hazy skies due to smoke. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thursday and into early next week, the chance of showers and storms will stay mainly in the higher terrain although a couple could spread onto the adjacent plains. The primary threat with any thunderstorms will be locally heavy rainfall which could result in flash flooding in the burn areas. Otherwise, it will be warm with slightly above normal temperatures. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight.
The Cheyenne radar (KCYS), 87 km away, was scanning. The volume nearest the first event began at 23:32 UTC.
1 flash flood. Local standard time, as filed.
A debris flow moved into Black Hollow Gulch and damaged or destroyed several structures including four homes. Four people in one of the homes perished when their residence washed away in the floodwaters.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Flash Flood, Larimer | 2021-07-20 | 57 | Female | Permanent Home | Direct |
| Flash Flood, Larimer | 2021-07-20 | 61 | Male | Permanent Home | Direct |
| Flash Flood, Larimer | 2021-07-20 | 59 | Female | Permanent Home | Direct |
| Flash Flood, Larimer | 2021-07-20 | 85 | Male | Permanent Home | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2021Every state in 2021This day in weather historyWarnings in Colorado, July 2021
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: 971685.