An area of low pressure trekking over southwest Colorado was absorbed into a broader Pacific trough that lifted across the Western Slope. This led to scattered to widespread showers and thunderstorms.
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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 GJT wrote it up.
An area of low pressure trekking over southwest Colorado was absorbed into a broader Pacific trough that lifted across the Western Slope. This led to scattered to widespread showers and thunderstorms. Some storms produced heavy rain which led to localized debris flows across portions of west-central Colorado over the course of a couple of days.
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 Grand Junction, CO wrote its last area forecast discussion before the first event at Sep 28, 1:41 PM MST, 1 hour 19 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 241 PM MDT Tue Sep 28 2021 .SHORT TERM...(Tonight through Wednesday night) Issued at 241 PM MDT Tue Sep 28 2021 Plenty of ongoing convection at this hour across eastern Utah and western Colorado. The cutoff low that is driving much of this activity is currently centered over Saguache and Alamosa counties, and will continue to drift northeast through the afternoon and evening. As such, activity will drift north as well, shifting from the southern and central mountains to favor the central and northern mountains into the overnight. Also at this time, the very outer-most influence of the Pacific trough is being felt across eastern Utah, with a line of stronger showers and storms forming just ahead of it across southern Uintah county and into Rio Blanco county in Colorado. As these storms are moving slower, and the stronger cells are putting down rainfall rates of 0.50-1.0 inches per hour, opted to put out a Flash Flood Watch for the Grizzly Creek Burn Scar through 9 PM tonight. This watch may be extended into the overnight should precipitation remain more convective in nature. With that being said, do expect precipitation to become more stratiform through the overnight hours. The energy associated with the no-longer-cut-off low pressure will have moved out into eastern Colorado, and the best energy from the Pacific trough likely won't have reached eastern Utah yet, so without daytime heating to provide instability, stratiform precipitation with embedded convection seems the best bet. The best energy from the trough finally begins to move through eastern Utah and western Colorado around daybreak Wednesday, with several rounds of showers and thunderstorms expected throughout the day. Again, the areas along and north of I-70 will be favored, but the higher terrain of the San Juans and southern Divide will likely see precipitation as well. So really, with this system the question isn't "if" much of the area will see a wetting rain, but rather how much will fall. QPF the last several days has been bullish, and have lowered storm total QPF with this package, but currently much of the area is looking to receive 0.25-0.50 inches through Thursday night, with higher amounts where the stronger convection is expected. Aside from the precipitation, the other story is the much cooler temperatures for Wednesday. Every forecast package seems to have lower afternoon highs for tomorrow, and this package is no exception. Temperatures tomorrow will be running 10-15 degrees below normal, even close to 20 degrees below normal in some spots! And while low temperatures tonight are expected to remain a few degrees above normal, thanks to clouds and precipitation, tomorrow night is forecast to run 5-10 degrees colder. With combination of cooler temperatures and precipitation, the tippy top peaks along the Divide may even see some snow! So, overall, the next two days are looking chilly. damp, and downright fall like. .LONG TERM...(Thursday through Tuesday) Issued at 241 PM MDT Tue Sep 28 2021 Medium to long-range guidance is coming into better agreement with the evolution of the trough that will be over the area on Thursday. The GFS continues to close off a low at the base of the trough, over central Arizona and New Mexico. Through Friday, this closed low will slowly move east-northeastward. As one would expect, the heaviest precip is progged to fall near the strongest lift which will remain near the center of the low while models continue to highlight precip over the spine of the Divide from about Vail Pass down to the New Mexico border. CAPE is very low while some midlevel is present though that, too, is weak so some showers and a few storms can be expected from Thursday afternoon through early Friday morning. Synoptic features are somewhat different with the EC but the end result is the same. The EC is opting for more troughiness before closing a low off Friday morning, over the same spot as the GFS. The end result? Almost the same areas look to receive precip as suggested by the GFS. Looks like the models are finally coming into better agreement...we'll see what the next model cycle brings. As far as the weekend is concerned, the GFS keeps us completely dry as the CWA becomes sandwiched by a deep low off the southwestern Pacific coast and a weak area of low pressure across MT. The EC also agrees on the two areas of low pressure but the trajectory of them is different and looks to bring some light precip on both Saturday and Sunday. Amounts look to be less than .2 inches so nothing to get excited about if the EC wins out. The trend continues Monday and Tuesday as the GFS keeps us dry while the EC brings a weak shortwave to our southern neighbors and might bring some precip so the southern valleys and San Juans. Still a bit of a toss up so we'll just have to see how things pan out. High temps will be right around seasonal values Thursday and Friday and then jump about 3 to 5 degrees above seasonal values for the work week. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1140 AM MDT Tue Sep 28 2021 Showers, rain, and thunderstorms will be common over the next 24 hours for all TAF sites. While VFR conditions will remain predominant, some brief MVFR will still be possible under and near the stronger showers/storms. Included VCTS and Tempo groups with -TSRA for all TAF sites from this afternoon onwards as a low and approaching cold front will both work on available moisture to produce said convection. There may be a lull in activity from 00 to 03Z before another round of showers/storms moves across the area. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Flash Flood Watch until 9 PM MDT this evening for COZ008-010-013. UT...None. && SHORT TERM...BGB LONG TERM...TGR AVIATION...TGR
Hazardous Weather Outlook National Weather Service Grand Junction CO 436 AM MDT Tue Sep 28 2021 COZ001>014-017>023-UTZ022>025-027>029-291045- Lower Yampa River Basin-Central Yampa River Basin- Roan and Tavaputs Plateaus-Elkhead and Park Mountains- Upper Yampa River Basin-Grand Valley-Debeque to Silt Corridor- Central Colorado River Basin-Grand and Battlement Mesas- Gore and Elk Mountains/Central Mountain Valleys- Central Gunnison and Uncompahgre River Basin- West Elk and Sawatch Mountains-Flat Tops- Upper Gunnison River Valley-Uncompahgre Plateau and Dallas Divide- Northwest San Juan Mountains-Southwest San Juan Mountains- Paradox Valley/Lower Dolores River- Four Corners/Upper Dolores River-Animas River Basin- San Juan River Basin-Southeast Utah-Eastern Uinta Mountains- Eastern Uinta Basin-Tavaputs Plateau-Arches/Grand Flat- La Sal and Abajo Mountains-Canyonlands/Natural Bridges- 436 AM MDT Tue Sep 28 2021 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Showers and storms will spread northward today and become more widespread this evening as another storm system pushes in from the west. Storms will be capable of brief moderate rain and wind gusts to 40 mph. The focus shifts across areas along and north of I-70 for the best precipitation potential this evening into the overnight hours. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Showers and storms will continue on Wednesday as a Pacific disturbance tracks across the northern portion of the forecast area. Temperatures will be much cooler with below normal readings. Drier air pushes in from the west late in the week with afternoon storms possible over the high terrain along the divide. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The national radar mosaic for the moment the first event began.
2 debris flow. Local standard time, as filed.
Burn scar debris flow from the Pine Gulch Fire flooded a house and rerouted Roan Creek at a bend 15 miles northwest of De Beque. Water marks along South Dry Fork Road were 3 to 6 feet high.
An NWS employee reported 6 to 8 inches of water and mud flowing across a driveway in a residential area as a result of heavy rains.
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, September 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: 977476, 977477.