An unsettled northwesterly flow aloft brought in a series of embedded upper level disturbances that produced scattered to numerous showers and thunderstorms across western Colorado. Significant rainfall occurred with some storms which resulted in mudslides and flash flooding in portions of the state.
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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 unsettled northwesterly flow aloft brought in a series of embedded upper level disturbances that produced scattered to numerous showers and thunderstorms across western Colorado. Significant rainfall occurred with some storms which resulted in mudslides and flash flooding in portions of the state.
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 Aug 4, 11:05 AM MST, 1 hour 55 minutes earlier.
Area Forecast Discussion National Weather Service GRAND JUNCTION CO 1205 PM MDT Fri Aug 4 2017 .SHORT TERM...(Today through Saturday) Issued at 359 AM MDT Fri Aug 4 2017 Few light showers trying to hang around early this morning over the central mountains, but convection has ended for the most part early this morning. Skies clearing across our forecast area with a less active morning expected. Latest models showing several weak ripples in the upper level flow will be passing through over the next 48 hours with precipitable water values climbing to near an inch. The 00Z/FRI soundings (last evening) came in a smidge over eight tenths of an inch. Radar estimated rainfall over the past 24 hours showing anywhere from nothing to over an inch in a few pockets where we saw stronger convection last evening (mainly of east-central Utah). Continue to interrogate the 4km NAMNest across our forecast area and it did a decent job with the morning convection yesterday. Today it is indicating convection firing over the central and southern mountains between 11 am and Noon MDT with activity increasing through the afternoon hours over most of our ridges. Convection pushes across valleys this evening with a a slightly more organized wave expected to drive across the San Juans and adjacent southern valleys. Latest nested NAM getting a bit bullish with convection through the evening hours from Cortez into Durango and Pagosa Springs between 7 pm and 3 am with a secondary wave arriving around sunrise. GFS hinting at some sort of wave as well push through the southern valleys overnight. Will nudge pops up to account for this possibility with northern zones dropping off to nothing after midnight. Another round of diurnally driven convection will arrive Saturday afternoon and evening. Models not showing a ton of upper support, so expect convection to decrease rather quickly around sunset Saturday evening. Temperatures will be running right around seasonal norms over the next couple of days. .LONG TERM...(Saturday night through Thursday) Issued at 359 AM MDT Fri Aug 4 2017 Expect cool and unsettled weather to continue through this extended period as the upper level ridge remains parked to our west. This will keep light northwest flow aloft in place with moisture pooling over the Central Rockies. H7 temps forecast to drop below 10C by Sunday night and again Monday night, giving an early fall feel to temperatures with scattered showers and thunderstorms during the afternoon and evening hours. Have already had reports of high elevation snow/graupel associated with convection (at and above the 14k level) and would not be surprised to see a bit more of that Monday and Tuesday. Not much change for Wednesday or Thursday as the northwest flow pattern remains locked in place. Latest CPC 2 week outlook continues to favor the cooler and wetter pattern holding. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1150 AM MDT Fri Aug 4 2017 Convection has just started firing over the higher terrain this morning and will continue to do so for the remainder of the afternoon into the evening. Increased moisture will allow some of the showers and storms to produce heavier rain. Confidence is increasing so VCTS remains in the forecast for most TAF sites. Some convection looks to persist overnight. Brief MVFR or even IFR may be possible if any of the stronger cells move over TAF sites. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...JDC LONG TERM...JDC AVIATION...TGR
Hazardous Weather Outlook National Weather Service GRAND JUNCTION CO 519 AM MDT Fri Aug 4 2017 COZ001>014-017>023-UTZ022>025-027>029-051200- 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- 519 AM MDT Fri Aug 4 2017 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Expect scattered showers and thunderstorms today and tonight across eastern Utah and western Colorado. Locally heavy rain, small hail and gusty winds to 40 mph are all possible with the strongest storms. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Isolated to scattered showers and thunderstorms are expected each afternoon and evening through next week with gusty outflow winds, small hail and heavy rain possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected today or tonight, however spotters are encouraged to relay rainfall amounts or any observed flooding to the National Weather Service in Grand Junction.
The Grand Junction radar (KGJX), 87 km away, was scanning. The volume nearest the first event began at 20:00 UTC.
2 debris flow, 2 heavy rain, 1 flash flood. Local standard time, as filed.
The Colorado Department of Transportation was sent by law enforcement to remove debris over Colorado Highway 141 near mile marker 95 as a result of excessive rainfall.
A series of strong thunderstorms produced torrential rainfall in the Elk Run subdivision which resulted in water that flowed into several homes. A home on Red Tail Court took the brunt of water flowing off the hillside and had two feet of water in the lower level. Some of the streets in Elk Run were coated with as much as 6 inches of mud. Radar estimated 1 to 1.5 inches of rain fell throughout the day.
In addition to pea sized hail, 0.60 inches of rain fell within 40 minutes.
As a result of heavy rains, several streets were flooded with water up to a foot deep that ran across the roadway in Carbondale, including the intersection of Village Road and Highway 133, as well as west Main Street and Highway 133.
A mudslide occurred on County Road 117 at mile marker 9 due to heavy rain from thunderstorms.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2017Every state in 2017This day in weather historyWarnings in Colorado, August 2017
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: 713008, 717931, 713009, 713011, 713010.