Heavy rain produced additional flash flooding where there was some culvert damage east of Williams Fork River on Kinney Creek Road.
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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.
Heavy rain produced additional flash flooding where there was some culvert damage east of Williams Fork River on Kinney Creek Road.
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 23, 2:03 PM MST, 1 hour 27 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 303 PM MDT Fri Jul 23 2021 .SHORT TERM...(This evening through Saturday) Issued at 236 PM MDT Fri Jul 23 2021 On satellite, the axis of anticyclonic circulation appear to be along the I-76 corridor this afternoon, with SW-NE cloud motions north of the boundary, with NE-SW movement south of the boundary. All of the thunderstorm activity has occurred along and north of the dry air on water vapor imagery. Coverage is increasing over the mountains at this time, with precipitable water values 0.8-0.9 inch over the mountains, and 1.1-1.3 inches over the northeast plains. CSU sounding taken at 1730Z this morning, showed a weak cap around 500 mb, which may have helped to limit or at least delay the stronger thunderstorm development. Outflow/cool front moving south through central Weld County at this time. Some showers/storms developing along this boundary as well. Best chance of storms will be through mid evening, then weakening overnight. The models show the easterly wave over southern New MX tonight, moving into southern AZ by Saturday aftn. 700/500 layer mixing ratios around 8c/km this afternoon drop to around 6c/km on Saturday. WPC shows a marginal risk of flash flooding over the mountains Saturday afternoon. 700/300mb layer winds on Saturday weak southeasterly. This will result in near stationary storm motions. Threat of flash flooding still there, but will hold of on another flash flood watch for Saturday at this time. .LONG TERM...(Saturday night through Friday) Issued at 236 PM MDT Fri Jul 23 2021 Long term period dominated by western ridge and eastern trough. Ridge is relatively flat through the weekend as an area of low pressure and cyclonic flow spins its way west across southern NM and AZ under the ridge. With low passing to the south the monsoonal flow gets cut off, although residual moisture will remain for the weekend. Ridging builds over the Rockies from Monday onward. For Sunday, surface based CAPE in excess of 1000 j/kg mainly on the plains, and 500-1000 in the mountains for thunderstorms. Precipitable water Sunday still near Saturday's levels, with 1-1.25" on the plains and .8-1 inch in the mountains. With the flatter ridge area of enhanced jet level wind passes through southern Wyoming, and may help enhance storm development in the north. Given high PWATs and some weak synoptic lift, threat for burn area flooding continues. For Monday onward, precipitable water drops to .75 mountains to 1 inch plains. Pops decrease from Monday onward to chance/scattered in the mountains and generally dry on the plains. Expect usual afternoon showers and thunderstorms developing in the afternoon, drifting onto the adjacent plains late in the day. Warming trend with the building ridge, with highs on the plains in the upper 90s to around 100. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 236 PM MDT Fri Jul 23 2021 Mainly VFR expected through the perioid. Northeast winds will transition to north/northwest shortly, then to more of a drainage wind late this evening. Outflow boundaries in between these times will likely throw a monkey wrench into the pattern around 00z. Hi Res models not showing much activity around the terminals this afternoon, with better potential this evening. So the window for best thunderstorm chance could be more in the evening vs late afternoon. && .HYDROLOGY... Issued at 236 PM MDT Fri Jul 23 2021 For tonight, flash flood watch will remain in effect through this evening. The thunderstorms have produced generally weak to moderate showers so far, primarily over Cameron Peak, but storms developing elsewhere. Some movement with the storms, 5 to 10 mph. The main threat for heavy rain will be this afternoon, with activity decreasing in strength this evening. A similar scenario will play out on Saturday. It will be cooler with a slight decrease in moisture over northern CO. Threat for flooding will remain elevated but confidence not high enough to go with a flash flood watch for Saturday at this time. For Sunday, flash flood threat in the burn areas remain with plenty of moisture in the atmosphere. Better chances for more organized storms to the north - Cameron Peak area, decreasing to the south. From Monday onward drier air will reduce flood threat, although there will still be scattered afternoon showers and thunderstorms with slow movement. && .BOU WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until 9 PM MDT this evening for COZ032>035. && SHORT TERM...Cooper LONG TERM...Hanson AVIATION...Cooper HYDROLOGY...Cooper/Hanson
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1002 AM MDT Fri Jul 23 2021 COZ030>051-241615- 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- 1002 AM MDT Fri Jul 23 2021 ...A FLASH FLOOD WATCH IS IN EFFECT FROM 11 AM MDT THIS MORNING THROUGH THIS EVENING FOR THE CAMERON PEAK, EAST TROUBLESOME, WILLIAMS FORK, AND CALWOOD BURN AREAS.... This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Scattered to widespread coverage of thunderstorms is expected over the higher terrain today with the stronger storms producing heavy rainfall. The Cameron Peak burn area will have a significant risk of flash flooding this afternoon. East Troublesome, Calwood, and Williams Fork burn areas will have an elevated risk for flash flooding. Coverage of storms will be higher across the urban corridor and plains today with lightning, gusty winds, and brief heavy rain being the primary threats. Highs will be in the mid to upper 90s across the plains. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Slow moving thunderstorms are expected again on Saturday and Sunday with a continued risk of flash flooding, especially on the burn areas. There may be a greater threat of flooding on the plains on Sunday. For Monday through Wednesday, there will be a drying trend with hot temperatures. There will still be a low risk of burn scar flooding Monday, then the risk will be very low for the middle of next week. Temperatures could be near 100 again on the plains by Tuesday. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight, however, rainfall reports from the burn scars would be extremely helpful.
Special Weather Statement
National Weather Service Denver CO
230 PM MDT Fri Jul 23 2021
COZ032>034-232100-
South and Southeast Grand/West Central and Southwest
Boulder/Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet CO-Grand and Summit Counties Below 9000 Feet CO-
South and East Jackson/Larimer/North and Northeast Grand/Northwest
Boulder Counties Above 9000 Feet CO-
230 PM MDT Fri Jul 23 2021
...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL GRAND AND
NORTHWESTERN BOULDER COUNTIES UNTIL 300 PM MDT...
At 229 PM MDT, Doppler radar was tracking a strong thunderstorm 6
miles northeast of Elkdale, or 49 miles southwest of Fort Collins,
moving northeast at 10 mph.
Penny size hail will be possible with this storm.
Locations impacted include...
Mt Audubon.
LAT...LON 4027 10574 4021 10558 4020 10559 4020 10557
4018 10553 4017 10553 4018 10552 4017 10550
3997 10571 4006 10590
TIME...MOT...LOC 2029Z 207DEG 9KT 4009 10577
SCHLATTERSpecial Weather Statement
National Weather Service Denver CO
250 PM MDT Fri Jul 23 2021
COZ034-232115-
South and Southeast Grand/West Central and Southwest
Boulder/Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet CO-
250 PM MDT Fri Jul 23 2021
...SPECIAL WEATHER STATEMENT...
At 248 PM MDT, Doppler radar was tracking a strong thunderstorm near
Blue River, or 3 miles southeast of Breckenridge, moving north at 5
mph. Additional strong thunderstorms are just east of Dillon and 2
miles north of Silverthone.
Half inch hail will be possible with these storms.
Locations impacted include...
Breckenridge, Silverthorne, Frisco, Dillon, Blue River, Keystone and
Copper Mountain.
LAT...LON 3969 10612 3960 10606 3966 10607 3969 10610
3970 10589 3938 10589 3937 10608 3960 10621
3961 10618 3964 10618 3965 10619 3966 10623
3968 10624 3968 10625 3969 10626
TIME...MOT...LOC 2048Z 167DEG 6KT 3944 10599
SCHLATTERThe Denver radar (KFTG), 130 km away, was scanning. The volume nearest the first event began at 22:30 UTC.
1 flash flood. Local standard time, as filed.
Heavy rain produced additional flash flooding where there is some culvert damage east of Williams Fork River on Kinney Creek Road.
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: 975994.