Isolated thunderstorms developed across portions of Douglas, Grand and Morgan counties. Microburst winds damaged boats on Grand Lake.
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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.
Isolated thunderstorms developed across portions of Douglas, Grand and Morgan counties. Microburst winds damaged boats on Grand Lake. One pontoon boat was lifted off the water and landed upside down near a home. In Larimer County, a brief period of heavy rain caused minor flash flooding in the Cameron Peak burn area near Glen Haven, along Miller Fork. In Douglas County, nickel size hail was observed. Lightning sparked a small grass fire near Wiggins in Morgan County.
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 4, 9:07 AM MST, 1 hour 38 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 1007 AM MDT Sun Jul 4 2021 .UPDATE... Issued at 951 AM MDT Sun Jul 4 2021 Morning soundings continue to show elevated PW values above 0.80 with dewpoints across the plains above 50 degrees. With temperatures expected to reach once again into the lower 90s, CAPE values will respond with 600 to 1200 J/KG possible by the late afternoon with increased storm potential as the cap erodes. Similar to yesterday, storms will form over the higher terrain and push ESE. With the upper ridge strengthening upper level flow has decreased slightly bringing slower moving storms and nudging burn scar flood projections into the limited category. Model soundings show less bulk shear today with PW values over an inch. This means storms will most likely stay sub severe with the main impacts being moderate to heavy rain, small hail and gusty winds with storms and outflows. Some outflows could aid in developing further convection, especially if they wander into more favorable antecedent conditions. Similar to yesterday storms should start to dissipate after 8 pm with just a slight chance of storms over southern Lincoln county after 9 pm. && .SHORT TERM...(Today and tonight) Issued at 350 AM MDT Sun Jul 4 2021 Skies are nearly cloud free over the CWA this morning. The exception being two small convective cells, one over north central Grand County, the other over central Douglas County. They were both move southeastward and I not certain if they are producing any rain down to the ground. Surface dew points are all in the mid and upper 50s F right now for the foothills and plains. Upper ridging is to continue its domination over the CWA's weather today and tonight. The weak northwesterly jet flow flow will continue along with benign synoptic scale energy through tonight. Also, more normal diurnal wind patterns will prevail in the low levels. Concerning today's convection, the precipitable water value progs look to change little with 1.00 inch plus numbers over the plains and 0.5 to 1.00 inch numbers over the mountains and foothills today and tonight. The best CAPE for today is over the mountains and foothills, with the highest values over the eastern border this evening. Now the models show the flow aloft to be a tad weaker later today and this evening compared to what they were yesterday. For pops, will continue with "scattered" coverage for the most part and will need to mention some burn area flooding potential. Today's high temperatures will be quite similar to Saturday's highs. .LONG TERM...(Monday through Saturday) Issued at 317 AM MDT Sun Jul 4 2021 Moisture will increase Monday and Monday night ahead of an upper level trough moving across Wyoming. Precipitable water values will climb above an inch over northeast Colorado. Temperatures around 90F and dew points near 50F yield about 500-1000 J/kg of surfaced based CAPE off the GFS model. Shear will be weak, so the main threat is expected to be heavy rain. Scattered to numerous thunderstorms are expected to form Monday afternoon and evening. Convection will decrease Monday evening, but some showers and thunderstorms will continue into the overnight hours and into Tuesday morning as the upper level trough drops southeast from Wyoming and moves across Colorado. Expect a cloudy mild night with lows in the 60s. This cloudiness will continue into Tuesday and keep highs in the 80s. The trough axis pushes through the area before peak heating Tuesday. The ECMWF shows a good amount and afternoon showers and thunderstorms. Meanwhile, the GFS and NAM indicate some drying Tuesday afternoon with most of the convection confined to southeast Colorado. By Tuesday evening, there's good agreement among the models with drier moving into the area with mostly clear skies expected by sunset. The upper level ridge over the Great Basin will intensify Wednesday and Thursday. This will bring warmer and drier conditions to Colorado. The warmest day of the week looks to be Thursday where highs are expected to be well into the 90s. A few low 100s will also be possible. Moisture will be limit with precipitable water values less than three-quarters of an inch. If any convection is able to form, would expect it to be high based with gusty winds and light rainfall. An upper level trough rounding the top of the ridge over Montana Thursday night will send a cold south through northern Colorado late Thursday night or early Friday. This is expected to drop highs by about 10F for Friday and Saturday. At this time, still doesn't appear to be enough moisture and instability for afternoon convection Friday. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 951 AM MDT Sun Jul 4 2021 VFR conditions are expected through the TAF period. Winds will be light and variable through 18z before they turn more NE and north with convection starting over the higher terrain by 20z. Storms could produce gusty outflow winds at BJC and DEN after 21z with some gusting up to 30-35 mph. Storm potential will be higher at BJC and APA after 22z with DEN seeing VCTS most likely. Conditions will improve after 01z with drainage expected by 04z. && .HYDROLOGY... Issued at 401 AM MDT Sun Jul 4 2021 Scattered thunderstorms are expected this afternoon and early evening over the western two-thirds of the CWA. Moisture levels remain pretty high and the storm motion should be around 15 mph. So, there will be a moderate threat of burn area flash flooding this afternoon. Scattered to numerous thunderstorms are expected Monday afternoon and evening. Heavy rainfall will accompany the stronger storms and elevated the flash flood threat across the burn areas. The airmass begins to dry Tuesday afternoon. Afternoon showers and thunderstorms will be possible again Tuesday. However, fewer storms are expected and they should be slightly weaker. This will result in a lower flash flood threat for the burn areas. High pressure strengthens over Great Basin Wednesday and Thursday. This will bring a warmer and drier trend with little to no rainfall expected in the latter half of the week. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && UPDATE...Bowen SHORT TERM...RJK LONG TERM....Meier AVIATION...Bowen HYDROLOGY....Meier/RJK
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1111 AM MDT Sun Jul 4 2021 COZ030>051-051715- 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- 1111 AM MDT Sun Jul 4 2021 This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...This Afternoon and Tonight Scattered thunderstorms will be possible this afternoon and into the early evening hours. Storms will form over the higher terrain and move east to southeast across the Metro area after 1 pm an then the eastern plains after 3 pm. Main impacts include moderate to heavy rain, small hail, gusty winds, and lightning. Conditions will improve after 8 pm across the region. Temperatures today will be warm again with highs reaching into the 70s across the higher terrain and 90s over the plains. Tonight will be another mild evening with lows in the upper 50s to lower 60s under party cloudy skies. .DAYS TWO THROUGH SEVEN...Monday through Saturday Scattered to numerous thunderstorms are expected Monday afternoon and evening with heavy rain possible. This will elevate the flash flood threat over the burn areas. Another round of showers and thunderstorms will be possible Tuesday before drier air moves into the region for Wednesday. This will be the start of a warmer and drier period for the latter half of the week. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight, but reports of heavy rain, flooding and hail will be appreciated.
The Denver radar (KFTG), 121 km away, was scanning. The volume nearest the first event began at 17:45 UTC.
2 hail, 1 thunderstorm wind, 1 flash flood, 1 lightning. Local standard time, as filed.
Strong microburst winds damaged several boats at Grand Lake. Two large pontoon boats were lifted out of the water, one landed upside down near a home.
Larimer County Sheriff reported flash flooding near Glen Haven. An estimated 1.2 inches of rain fell in one hour. The areas around Steamside Drive and Fishermans Lane just north of Glen Haven were most impacted by floodwaters from Miller Fork.
Lightning sparked a grass fire.
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: 971631, 971628, 971660, 971629, 971630.