One flash flood occurred on Coal Creek. A nearby spotter measured 5 inches of rainfall during the event.
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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.
One flash flood occurred on Coal Creek. A nearby spotter measured 5 inches of rainfall during the event. In the next event, a flash flood reportedly moved several vehicles along with some heavy equipment.
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 30, 7:06 PM MST, 2 hours 9 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 806 PM MDT Wed Jun 30 2021 .UPDATE... Issued at 752 PM MDT Wed Jun 30 2021 N/S oriented boundary moving west of US 85 toward I-25, with a surface cyclonic circulation just west of DIA. Boundary along with surface based CAPE 500-1000 j/kg along the I-25 corridor & along the Palmer divide this evening supporting widely scattered convection. Persistent slow moving cluster of thunderstorms in northwest Weld county, and raised pops in that area for a few more hours. Other showers in the vicinity of KDEN popping up and dissipating, not even making thunder. Lowered pops through midnight northeast plains where nothing is going on yet. HRRR remains bullish on bringing showers out of the foothills and along Palmer Divide, and left chances down there overnight spreading onto the eastern plains after midnight. Tweaked the POPs with this update, blended in current temperatures, and left the overnight lows alone. && .SHORT TERM...(This evening through Thursday) Issued at 240 PM MDT Wed Jun 30 2021 Scattered showers and thunderstorms have begun to form across the higher mountains and east slopes early this afternoon. So far, instability is marginal with CAPE VALUES 400-800J/KG while storm motions around 10kt. There has been just enough motion to keeping storms moving to prevent any major flooding across higher terrain. Across lower elevations, outflow boundaries may spark storms later this afternoon and evening which most models are picking on best focus for storms east and south of Denver and across Palmer Divide. Confidence is low on how far east the convection develops this evening, but certainly coverage more isolated out on the plains. The 50kt jet streak across southeast Colorado does slowly sag further south and east but still may have some interaction in shower development overnight and will keep in some low pops. The southeast low level flow also appears to drag in additional moisture from Kansas. Will also have chances of showers across the plains in the morning as well. The main concern for Thursday is a higher threat of flash flooding across the burn scars and adjacent areas in the mountains and adjacent plains. The weak upper trof remains across Utah with a continued light southwest flow aloft over Colorado. There is a definite upswing of moisture across the area with precipitable water values up over an inch across all the plains. The model forecast instability increases with SFC based CAPES increasing upwards of 1500j/kg. However with increased cloud cover, wondering if will come up a bit short and actual CAPES remaining under 1000j/kg. It also appears storm motions may end up being similar to today with 10kt storm motion from the west and southwest. The latest HRRR reflectivity of storms has actually surprisingly decent storm motions which would reduce the flash flood threat. Regardless, the threat will be higher on Thursday afternoon then today, but confidence not high enough to issue a flash flood watch. Temperatures will be a bit cooler with more cloud cover than today. Will still go with likely pops in most areas Thursday afternoon given the moisture uptick, so overall not many changes in forecast. .LONG TERM...(Thursday night through Wednesday) Issued at 240 PM MDT Wed Jun 30 2021 Isolated areas of heavy rainfall will likely continue into the early overnight hours Thursday night. Activity should decrease fairly quickly after sunset surface stability increases, with just a few overnight showers after midnight. Friday's pattern is largely the same as Thursday, with a few subtle differences. Temperatures are likely to be just a little warmer, with surface dew points a couple degrees drier. GFS/ECM both suggest that CAPE across the area will be almost identical to Thursday. Forecast soundings show mean-cloud layer flow of about 10kt during the afternoon, with a fairly shallow warm cloud layer. Still, the current thought is that heavy rainfall will continue to be a concern over most of the high country. PWATs will still be near an inch across the Foothills and near 3/4 of an inch west of the divide. Guidance does try to keep the convective focus across our higher terrain unlike Thursday, and the primary concern for the day will be for burn area flash flooding. The pattern does slowly get warmer and drier this weekend, with chances for afternoon thunderstorms both Saturday and Sunday. The flow aloft does strengthen a touch both days, which should lead to slightly faster storm motions, but there will likely be some flash flooding concerns again over our burn areas. Highs across the plains will reach the upper 80s to low 90s. Monday will perhaps be the driest day of the week, with scattered storms for the mountains and an isolated storm or two along I-25. A shortwave should bring a push of slightly cooler air and increased thunderstorm coverage, with more uncertainty Wednesday and beyond. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 543 PM MDT Wed Jun 30 2021 VFR, with scattered showers and maybe a rumble of thunder this evening. We left VCTS in for Denver through 02z in lingering instability and colliding outflow boundaries, then VCSH for a few more hours. Hi resolution models showing a band of convection moving out of the foothills and through the TAF sites 03-05z so left VCSH through then. Boundary/Denver Convergence Zone has set up NNE/SSW oriented, just west of KDEN and KAPA and just east of KBJC. Forecast it to remain stationary through the evening. Toward morning a Denver Cyclone will set up again, but details on where are elusive. For the TAF went with HRRR model solution, with SSW wind becoming east in the afternoon, then Thursday afternoon convection after 20z. && .HYDROLOGY... Issued at 240 PM MDT Wed Jun 30 2021 Thunderstorms so far have been on the weaker side in the mountains this afternoon given the marginal instability while storm motions are moving storms enough to limit the threat for flooding. There will be an increasing threat of flash flooding over the burn scars on Thursday afternoon with higher moisture levels. However storm motions again maybe quick enough to prevent any major flooding. For now confidence too low to issue a flash flood watch. Elevated flash flooding threat will continue on Friday with slow moving thunderstorms likely again across the burn areas. There is some uncertainty regarding the amount of moisture and instability available Friday afternoon, but conditions will generally be similar to Thursday. The flash flooding threat should decrease through the weekend as the pattern gradually turns warmer and drier, but heavy rainfall will still be possible each day with scattered thunderstorms likely. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && UPDATE...Hanson SHORT TERM...Entrekin LONG TERM...Hiris AVIATION...Hanson HYDROLOGY...Entrekin/Hiris
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 944 AM MDT Wed Jun 30 2021 COZ030>051-011545- 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- 944 AM MDT Wed Jun 30 2021 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Today will be slightly warmer with a better chance of thunderstorms this afternoon and evening as moisture levels have increased over the area. The coverage of thunderstorms will be greatest in the high country and Palmer Divide regions. The strongest storms will produce very heavy rain and wind gusts to 40 mph. Locally heavy rainfall associated with the slow moving thunderstorms will elevate the flood threat, especially in the burn areas. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Thunderstorm activity will increase for Thursday and Friday. Storms will be slow moving and some will produce rainfall of one to two inches in an hour or two, which could produce significant flooding if it occurs over one of the new burn areas. The threat is greatest over the east slopes of the Front Range Thursday and Friday in the afternoon and evening hours. There is a substantial threat for the burn areas in Grand county as well. Minor flooding is possible from heavy rainfall in other areas. For the weekend into early next week, it will be a little warmer with some decrease in thunderstorm activity, but there will still be a threat of heavy rain with some of the storms. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight, but reports of heavy rain would be appreciated.
The Cheyenne radar (KCYS), 38 km away, was scanning. The volume nearest the first event began at 04:12 UTC.
2 flash flood. Local standard time, as filed.
A storm produced 5 inches of rain along Coal Creek, followed by flash flooding.
Heavy rain produced flash flooding. The floodwaters moved several cars, along with some heavy equipment.
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: 969070, 969073.