Heavy rainfall associated with a thunderstorm in the Cameron Peak burn area, produced flash flooding in Masonville. Heavy rainfall, up to one inch in an hour, produced flash flooding along Buckhorn Road, south of Big Bear Road.
Every event with a place to put it. Tap one for its entry below.
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 rainfall associated with a thunderstorm in the Cameron Peak burn area, produced flash flooding in Masonville. Heavy rainfall, up to one inch in an hour, produced flash flooding along Buckhorn Road, south of Big Bear Road. Running water, up to 6 inches deep, covered the roadway. Heavy rain also produced minor flooding in the East Troublesome burn area. Runoff from that storm impacted a small section of Trail Ridge Road along Onahu Creek. A swath of black water, approximately 100 yards wide and 5 inches deep, inundated the roadway briefly and lasted only about 5 minutes. Trail Ridge Road was closed temporarily to clear away the mud. There were some minor mud and flooding issues on Green Mountain Trail too. Finally, a severe thunderstorm produced hail up to quarter size in southwest Boulder.
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 Jun 25, 9:48 AM MST, 27 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 1048 AM MDT Fri Jun 25 2021 .UPDATE... Issued at 1038 AM MDT Fri Jun 25 2021 Radars are indicate ongoing showers over Logan, Sedgwick and Larimer Counties at this time. There is also some newly developing convection over the Cheyenne ridge in northern Weld county. Satellite pictures are showing convective cloudiness developing over the mountains, foothills and Palmer Ridge. Water vapor pictures are showing a disturbance, within the upper trough, over northwestern Colorado with some convection developing there. This may eventually affect the CWA later in the day. Well over half the CWA is sunny or mostly sunny still this mid/late morning. The temperature at DIA is the same as it was yesterday at this time. Current readings across the plains are a tad warmer than the GFE hourly temperatures indicate. May up afternoon highs a bit. Will leave the "likely" pops in the GFE grids for this afternoon and evening. Perhaps with a bit more sun/energy, storms may be stronger. && .SHORT TERM...(Today and tonight) Issued at 350 AM MDT Fri Jun 25 2021 A broad trough is currently over the Colorado area with a small shortwave passing across northeast Colorado. This shortwave is producing rain showers mainly north and east of DIA. These showers will continue into the morning hours especially across the far northeast corner of the state where there is better moisture in place. Nighttime microphysics satellite data shows a good amount of clearing across the western and southern part of Colorado this morning. This clearing should move over at least the southern half of our CWA which should allow for some heating today. However, highs will be cooler than yesterday's by 5 to 10 degrees as cooler air aloft moves over. Considering the daytime heating and cooler air aloft, moderate instability will develop across the plains this afternoon with mixed layer CAPE above 1,000 j/kg in spots. This instability will allow storms to develop initially over the higher terrain and then onto the plains. Model soundings show there will be weak low level winds across the plains which will limit storm inflow and effective bulk shear. The convective mode will likely be multicellular with line segments capable of producing severe wind gusts. This wind threat could warrant the need for a Severe Thunderstorm Watch this afternoon. The severe hail threat will be lower than the wind threat although a couple severe hail reports will be possible in Lincoln and Washington counties where the best instability will be. Models show a cold front-like feature moving south of out Wyoming this afternoon reaching the Denver metro area around 5-6pm. It should be a focus for storms to form and the last couple runs of the HRRR have a good amount of rainfall coming down in the Denver metro area as a result of this boundary. It seems plausible to me but accuracy on the HRRR at this lead time can be rough. Showers and storms will continue tonight mainly along the foothills and adjacent plains as a shortwave trough moves southward across the area. Low temperatures will be a few degrees below normal with mid 50s across the plains and 30s and 40s across the higher terrain. .LONG TERM...(Saturday through Thursday) Issued at 322 AM MDT Fri Jun 25 2021 A weak upper level trough will still affect the area on Sat as another surge of cooler air moves into nern CO. Still could see showers in the morning, mainly south of I-70, across the higher terrain. By aftn, there will be enough instability to produce a good chc of showers and a few storms over the higher terrain. Across the plains expect less coverage where MLCAPE will be under 500 j/kg. Highs will be in the upper 60s to mid 70s over nern CO. For Sun into Mon a blocking upper level high will reside over the Pacific Northwest, with an elongated upper level trough, extending from the northern High Plains into ern CO. In addition, will see another reinforcing shot of cool air, affecting the plains on Sun. Overall instability will remain on the low side with MLCAPE remaining at or blo 500 j/kg. However, due to position of the upper level trough and lingering moisture, will probably see sct showers and a few storms both days mainly in the aftn. Highs both days, across the plains, will remain 10 to 15 degrees below normal. Looking ahead to Tue into Wed, the blocking upper level high will generally stay stationary over the nwrn US. There still may be some extension of the upper level trough remaining over ern CO. Thus this would lead to below normal temps with a lingering chc of showers and a few storms both days. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1038 AM MDT Fri Jun 25 2021 Light and variable winds are the rule a DIA this morning. Models are still showing some northerly winds to move in around 21Z. Will leave the tempo group in for thunder and may need another one into the later evening hours. May need to put more rain in through the evening hours as well. Cross sections indicate that some BKN- OVC025-040 ceilings are possible this evening and much of tonight. && .HYDROLOGY... Issued at 350 AM MDT Fri Jun 25 2021 Scattered to numerous storms are expected over the burn areas this afternoon and evening. Precipitable water values will be a bit above normal today with values around 0.80 to 0.90 in Denver. Any storms that do form over the burn areas will have decent motion with them such that they will not stall over the same location for a long time. In addition, instability values over the burn areas will not be very high which should limit the rainfall rates slightly. With all that being said, the multiple rounds of storms with moderate to briefly heavy rainfall could pose a flash flooding risk. I considered putting a limited threat in the burn area flood matrix for all the burn areas but model QPF forecasts are showing the possibility of heavy rainfall amounts east of the Continental Divide. Therefore, there is an elevated threat for flash flooding in the Cameron Peak and Calwood burn areas and limited for the other two. I am somewhat confident that there will be a couple flood advisories issued today although a major flood is very unlikely. There will be a chance of afternoon showers and thunderstorms Saturday through Monday. The risk of flash flooding, in any of the burn scars, will be rather limited each day. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && UPDATE.......RJK SHORT TERM...Danielson LONG TERM....RPK AVIATION.....RJK HYDROLOGY....Danielson/RPK
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1056 AM MDT Fri Jun 25 2021 COZ030>051-261700- 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- 1056 AM MDT Fri Jun 25 2021 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Scattered thunderstorms have already developed over northern Larimer and Weld counties this morning. They are also just beginning to develop over the higher terrain. Showers and thunderstorms are likely across most of the forecast area from mid afternoon well into the evening hours. Some of the storms could produce wind gusts up to 60 mph and one inch hail east of a line from Fort Morgan to Monument Hill. Multiple rounds of showers and thunderstorms are expected over the burn areas. They could produce flash flooding, but major flash flood is not expected at this time. Some showers and thunderstorms will linger across the plains overnight. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Saturday will remain cool with a good chance of showers and a few storms, mainly over the higher terrain. There will be a limited threat for flash flooding, mainly in the East Troublesome and Williams Fork burn areas. For Sunday and Monday, scattered showers and a few storms are expected with cloudy and cool conditions. The threat of flash flooding in the burn areas will be low both days. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Denver radar (KFTG), 126 km away, was scanning. The volume nearest the first event began at 17:16 UTC.
1 heavy rain, 1 hail, 1 flash flood. Local standard time, as filed.
Moderate to heavy rainfall associated with a thunderstorm produced minor flooding along Trail Ridge Road.
Heavy rain produced flash flooding near Masonville. Minor flooding was observed at the Masonville Post Office. There was a debris jam at the bridge. Black Creek Road in the Retreat was washed out in the storm. Both sides of the road were eroded by water flow making the it impassable. Big Bear Road was washed out from the paved road to the gate of nearby property. A recently installed culvert was washed out, and the road was impassable.
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, June 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: 969061, 968506, 968505.