A thunderstorm produced heavy rain and flash flooding in the Calwood burn area. Law enforcement reported a 3 to 4 foot surge of debris and water flowing down Geer Canyon.
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The episode as NWS BOU wrote it up.
A thunderstorm produced heavy rain and flash flooding in the Calwood burn area. Law enforcement reported a 3 to 4 foot surge of debris and water flowing down Geer Canyon. |The debris flow impacted stretches of Geer Canyon Drive and the lower part of Geer Canyon.
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 27, 2:00 PM MST, 3 hours 18 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 300 PM MDT Sun Jun 27 2021 .SHORT TERM...(This evening through Monday) Issued at 300 PM MDT Sun Jun 27 2021 Area radars are indicating a bunch of small convective cells pushing south-southeastward across the CWA at this time. The highest coverage is over the mountains and foothills from the divide eastward. SOme of these area producing small hail. They are moving about 20 mph and a few contain brief heavy rainfall. Nothing very significant at this time. Temperatures across the plains are in the upper 60s to mid 70s F at this time. Current soundings are showing a decent cap in place at about 550 mb. Models show decent convective coverage through the afternoon into about mid evening. The best CAPE is over the mountains and foothills. WIll keep the highest pops going there. Models never show the precipitation to end overnight. For convection on Monday, the highest CAPE, by far is over the mountains foothills again, especially south of I-70. Will hit the pops highest there. It will be a bit warmer on Monday and there will be a bit more moisture over the plains on the precipitable water fields. .LONG TERM...(Monday night through Sunday) Issued at 300 PM MDT Sun Jun 27 2021 No major impacts are anticipated for the long term period. Ensemble guidance has shown general agreement with the gradual breakdown of the blocking upper level ridge to the west and trough over Colorado. By mid- week, the ridge moves over Colorado contributing to the gradual warming trend with temperatures approaching seasonable values by Friday. Monday night, a few isolated showers and thunderstorms may linger, but high-resolution guidance shows them to taper off before midnight. The blocking ridge gradually moves east over Colorado by mid-week advecting higher heights. 700 mb temperatures increase through the end of the week supporting a slow warming trend. Temperatures are expected to approach normal values by Friday with highs in the mid to upper 80s over the lower elevations. There is a consistent signal shown in both deterministic and ensemble guidance for the transport of subtropical moisture from the southwest as a ridge sets up to the south. This will start advecting moisture into the region by mid-week. Each day will see a chance for afternoon showers and thunderstorms with the best chances over the higher terrain. Instability appears to be limited Tuesday with MLCAPE values less than 500 J/kg mostly over the higher elevations coupled with a signal for QPF. Kept higher PoPs over that region as a result. Instability values are more favorable Wednesday through the end of the week with bulk shear values around 20-25 kts. With sufficient moisture, scattered afternoon thunderstorms are possible through the weekend. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 245 PM MDT Sun Jun 27 2021 North-northwesterly winds continue and DIA. Models keep that going until mid evening. Weak, normal drainage patterns are expected tonight. Ceilings could get down to BKN040 if a decent shower/storm moves across the airport. Outflow winds from storms could gust to 35 knots. && .HYDROLOGY... Issued at 222 PM MDT Sun Jun 27 2021 The threat of flash flooding will be low later this afternoon and evening as the showers and thunderstorms are moving fairly fast. Training of cells over the mountains and foothills could result in some flooding, especially over the burned areas. The threat for flooding over the burn areas will be low. Instability will be sufficient enough to produce afternoon showers and thunderstorms each day, especially over the higher terrain. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && SHORT TERM....RJK LONG TERM.....Mensch AVIATION......RJK HYDROLOGY.....RJK/Mensch
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1046 AM MDT Sun Jun 27 2021 COZ030>051-281700- 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- 1046 AM MDT Sun Jun 27 2021 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight There will be another round of showers and thunderstorms from late this morning into the mid evening hours. The storms may produce brief heavy rain, small hail and gusty winds to 40 mph. The threat of flash flooding in the burn areas will remain low. .DAYS TWO THROUGH SEVEN...Monday through Saturday Continued mostly cloudy and cool on Monday, with scattered showers and a few storms are expected. Temperatures will gradually warm up through the rest of the period, but will remain cooler than normal for this time of year. There will be a chance of afternoon and evening showers and thunderstorms each day, especially over the higher terrain. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight.
Special Weather Statement National Weather Service Denver CO 424 PM MDT Sun Jun 27 2021 COZ040-272300- North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe Counties/East Broomfield County CO- 424 PM MDT Sun Jun 27 2021 ...SPECIAL WEATHER STATEMENT... At 424 PM MDT, Doppler radar was tracking a strong thunderstorm over southwestern Thornton, or 10 miles north of Denver, moving south at 15 mph. A brief funnel cloud was reported with this storm, but is not expected to touch down. Pea sized hail and winds in excess of 30 mph will be possible with this storm. Locations impacted include... Southwestern Thornton, southeastern Westminster, southwestern Commerce City, Northglenn and Federal Heights. LAT...LON 3992 10503 3993 10496 3979 10490 3980 10504 TIME...MOT...LOC 2224Z 359DEG 11KT 3987 10499 BARJENBRUCH
The Denver radar (KFTG), 76 km away, was scanning. The volume nearest the first event began at 00:20 UTC.
1 flash flood. Local standard time, as filed.
Heavy rain produced flash flooding in Geer Canyon in the Calwood burn area.
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: 968539.