Monsoon moisture advected into the region during the month of August. This led to cooler and unsettled conditions and brought some much needed precipitation to eastern Utah.
Every event with a place to put it; 7 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
Monsoon moisture advected into the region during the month of August. This led to cooler and unsettled conditions and brought some much needed precipitation to eastern Utah. As a result, drought conditions improved by one or more categories across some zones by the end of the month.
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 Jul 31, 10:37 PM MST, 1 hour 23 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1137 PM MDT Sat Jul 31 2021 .UPDATE... Issued at 1046 PM MDT Sat Jul 31 2021 This is the quietest the radar mosaic has been in days with lingering convection confined to the far southwest part of the CWA this evening. With the threat of widespread heavy rainfall gone in the eastern CWA the flood watch has been cancelled. |&& .SHORT TERM...(Tonight through Sunday night) Issued at 300 PM MDT Sat Jul 31 2021 High pressure has retrograded in response to the deepening mid- level trough over the center of the nation and was parked overhead early this afternoon. Subtropical moisture remained entrenched over the area with 1.08" precipitable water in the GJT 12Z/Sat sounding which is in excess of 150 percent of the climatological norm. As a result, storms were quick to erupt over higher terrain over eastern Utah, the San Juans, and portions of northwest Colorado where cloud cover was lacking this morning. Over the central part of western Colorado moist convection was hindered by cloud cover blanketing the area. As mentioned in previous discussions, convergence along the Continental Divide resulting from an eastward ridge-level wind component is expected to enhance thunderstorm development through the latter part of the afternoon and evening. This, combined with deep monsoonal moisture and light steering winds raises the heavy rain threat which increases the potential for mud/debris slides and flash flooding. In addition, both the NAMNest and HRW NSSL suggested the formation of a mesoscale convective vortex centered over the Gunnison Basin this evening. Therefore, the Flash Flood Watch which encompasses the Colorado mountains through midnight appears justified. With respect to the Gunnison Basin, given the potential for more persistent rain this evening under the MCV, have decided to add this area for inclusion in the watch. Especially in light of antecedent rainfall received Friday. The MCV is likely to keep showers and thunderstorms going through the night mainly in the vicinity of the MCV in southern and central Colorado. However, given the nuanced nature of the monsoon season, can't rule out some rogue cells forming elsewhere. High pressure remains atop the region on Sunday, and in contrast to the last couple of days, there doesn't seem to be any dynamic element which favors any one area. Storms will continue to be slow moving and moisture levels are expected to remain high. Therefore, though there will be numerous showers and thunderstorms across the area and the potential for localized flash flooding and mud/debris slides, will not issue a Flash Flood Watch with this package. Afternoon highs Sunday will continue to run cooler than normal due to clouds and shower/thunderstorm activity while overnight lows hew close to normal. .LONG TERM...(Monday through Saturday) Issued at 300 PM MDT Sat Jul 31 2021 The longwave mid-level height pattern will become highly amplified to start the new work week with the CONUS dominated by a trough- ridge- trough configuration. The Intermountain West will be directly underneath this ridge, allowing steering currents to funnel deep monsoonal moisture from the eastern Pacific, Gulf of California and Gulf of Mexico northward to the U.S./Canada border and beyond. In the path of that moisture will be eastern Utah and western Colorado, allowing for our relentless monsoon to continue. Showers and thunderstorms will once again fire across the high terrain midday into the afternoon on Monday before becoming more widespread and drifting off into the adjacent valleys during the evening. As has been the case for the last two weeks, the mesoscale setup for flash flooding is impressive. Instability evidenced by 1000-1500 j/kg of CAPE combined with high mid-level RHs and PWATs well above the 90th percentile will create an environment that is favorable for efficient rainfall production. More concerning however are the slow storm motions and the potential for training and back-building storms. So like a broken record, vulnerable drainages and our most prone and recent burn scars will need to be closely monitored for flooding, mudslides, debris flows and everything in between. Another intriguing aspect of this setup is a subtle shortwave trough attempting to push into the ridge from west to east across the Great Basin during the afternoon and evening. This may allow for just enough 0-6km bulk shear to organize storm updrafts over our CWA and produce a low- end severe weather risk. That said, models tend to be too progressive in a synoptic pattern like this, so confidence in the severe risk is pretty low at the moment. Still, the typical hazards with monsoonal convection remain, including gusty winds and small hail. Significant changes begin to take place Tuesday and especially Wednesday as the aformentioned ridge is progged by ensembles to break down over the Intermountain West and re-develop over the southern Great Basin. This will push the plume of monsoon moisture east into the Plains and cut off the source to our south. As a result, much drier air will filter into the forecast area from the northwest. There will be a noticeably drier feel to the air by Wednesday afternoon as PWATs drop by over half an inch and dew points fall into the 30s and 40s. Not to say that there won't be any showers or storms -- especially on Tuesday -- but activity will be much less from mid-week into the weekend and will primarily favor the high terrain along the Continental Divide. && .SHORT TERM...(Tonight through Sunday night) Issued at 300 PM MDT Sat Jul 31 2021 High pressure has retrograded in response to the deepening mid- level trough over the center of the nation and was parked overhead early this afternoon. Subtropical moisture remained entrenched over the area with 1.08" precipitable water in the GJT 12Z/Sat sounding which is in excess of 150 percent of the climatological norm. As a result, storms were quick to erupt over higher terrain over eastern Utah, the San Juans, and portions of northwest Colorado where cloud cover was lacking this morning. Over the central part of western Colorado moist convection was hindered by cloud cover blanketing the area. As mentioned in previous discussions, convergence along the Continental Divide resulting from an eastward ridge-level wind component is expected to enhance thunderstorm development through the latter part of the afternoon and evening. This, combined with deep monsoonal moisture and light steering winds raises the heavy rain threat which increases the potential for mud/debris slides and flash flooding. In addition, both the NAMNest and HRW NSSL suggested the formation of a mesoscale convective vortex centered over the Gunnison Basin this evening. Therefore, the Flash Flood Watch which encompasses the Colorado mountains through midnight appears justified. With respect to the Gunnison Basin, given the potential for more persistent rain this evening under the MCV, have decided to add this area for inclusion in the watch. Especially in light of antecedent rainfall received Friday. The MCV is likely to keep showers and thunderstorms going through the night mainly in the vicinity of the MCV in southern and central Colorado. However, given the nuanced nature of the monsoon season, can't rule out some rogue cells forming elsewhere. High pressure remains atop the region on Sunday, and in contrast to the last couple of days, there doesn't seem to be any dynamic element which favors any one area. Storms will continue to be slow moving and moisture levels are expected to remain high. Therefore, though there will be numerous showers and thunderstorms across the area and the potential for localized flash flooding and mud/debris slides, will not issue a Flash Flood Watch with this package. Afternoon highs Sunday will continue to run cooler than normal due to clouds and shower/thunderstorm activity while overnight lows hew close to normal. .LONG TERM...(Monday through Saturday) Issued at 300 PM MDT Sat Jul 31 2021 The longwave mid-level height pattern will become highly amplified to start the new work week with the CONUS dominated by a trough- ridge- trough configuration. The Intermountain West will be directly underneath this ridge, allowing steering currents to funnel deep monsoonal moisture from the eastern Pacific, Gulf of California and Gulf of Mexico northward to the U.S./Canada border and beyond. In the path of that moisture will be eastern Utah and western Colorado, allowing for our relentless monsoon to continue. Showers and thunderstorms will once again fire across the high terrain midday into the afternoon on Monday before becoming more widespread and drifting off into the adjacent valleys during the evening. As has been the case for the last two weeks, the mesoscale setup for flash flooding is impressive. Instability evidenced by 1000-1500 j/kg of CAPE combined with high mid-level RHs and PWATs well above the 90th percentile will create an environment that is favorable for efficient rainfall production. More concerning however are the slow storm motions and the potential for training and back-building storms. So like a broken record, vulnerable drainages and our most prone and recent burn scars will need to be closely monitored for flooding, mudslides, debris flows and everything in between. Another intriguing aspect of this setup is a subtle shortwave trough attempting to push into the ridge from west to east across the Great Basin during the afternoon and evening. This may allow for just enough 0-6km bulk shear to organize storm updrafts over our CWA and produce a low- end severe weather risk. That said, models tend to be too progressive in a synoptic pattern like this, so confidence in the severe risk is pretty low at the moment. Still, the typical hazards with monsoonal convection remain, including gusty winds and small hail. Significant changes begin to take place Tuesday and especially Wednesday as the aformentioned ridge is progged by ensembles to break down over the Intermountain West and re-develop over the southern Great Basin. This will push the plume of monsoon moisture east into the Plains and cut off the source to our south. As a result, much drier air will filter into the forecast area from the northwest. There will be a noticeably drier feel to the air by Wednesday afternoon as PWATs drop by over half an inch and dew points fall into the 30s and 40s. Not to say that there won't be any showers or storms -- especially on Tuesday -- but activity will be much less from mid-week into the weekend and will primarily favor the high terrain along the Continental Divide. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1133 PM MDT Sat Jul 31 2021 Vicinity thunderstorms will remain in the TAF overnight for KCNY as showers and thunderstorms are expected to linger. Otherwise, remaining TAF sites will see decreasing clouds and light winds following typical drainage patterns. Showers and thunderstorms are expected to kick off over the higher terrain tomorrow afternoon and potentially impact terminals. Winds will be gusty and erratic near storms. VFR conditions will prevail for the next 24 hours. && .HYDROLOGY... Issued at 300 PM MDT Sat Jul 31 2021 The continued threat for heavy rainfall and training storms through Monday may require additional Flash Flood Watches, so please stay up to date on the latest forecast. A downturn is possible by mid week as a slow, drying trend takes hold. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && UPDATE...15 SHORT TERM...NL LONG TERM...MDA AVIATION...TGJT HYDROLOGY...TGJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 400 AM MDT Sat Jul 31 2021 COZ001>014-017>023-UTZ022>025-027>029-011000- 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- 400 AM MDT Sat Jul 31 2021 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Widespread to numerous showers and thunderstorms are expected today with the best potential of heavy rain and flash flooding over the higher terrain of western Colorado and recent burn scars as deep monsoonal moisture remains. Storms will continue into the overnight hours. Expect heavy rain, frequent lightning, gusty outflow winds to 40 kts and hail with stronger storms. .DAYS TWO THROUGH SEVEN...Sunday through Friday Daily widespread to numerous showers and thunderstorms can be expected each day through early next week, with monsoon moisture entrenched across the area. Moderate to heavy rain, gusty winds and lightning will be the primary threats with storms. A downturn is possible mid to late next week with less coverage of storms. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
711 PM MDT SAT JUL 31 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0706 PM FLASH FLOOD 7 NE FRUITA 39.23N 108.64W
07/31/2021 MESA CO PUBLIC
FLASH FLOOD IN HUNTER CANYON 21 ROAD.
ESTIMATED 8 FEET OF WATER MOVING DOWN WASH.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
713 PM MDT SAT JUL 31 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0710 PM FLASH FLOOD 10 NNE LOMA 39.34N 108.74W
07/31/2021 MESA CO PUBLIC
10 FT WALL OF WATER OUTSIDE OF WASH.
EVACUATIONS IN ORDER FOR HOMES ALONG 16
ROAD.
&&The national radar mosaic for the moment the first event began.
7 drought. Local standard time, as filed.
The status of the drought improved across some of the zone through the month of August. Exceptional (D4) drought improved to the extreme (D3) category across the south with extreme conditions continuing elsewhere.
The status of the drought remained unchanged across the zone through the month of August. The extreme (D3) drought continued over all but the far eastern portion of the zone where severe (D2) conditions remained.
The status of the drought improved across some of the zone during the month of August. The exceptional (D4) drought improved to the extreme (D3) category over the southern portion of the zone while extreme conditions continued elsewhere.
The status of the drought remained unchanged across the zone during the month of August with extreme (D3) conditions across the entirety of the zone.
The status of the drought remained unchanged through the month of August with extreme (D3) conditions persisting across the entirety of the zone.
The status of the drought improved across much of the zone through the month of August. Exceptional (D4) conditions improved to the extreme (D3) category across all but the northeast portion of the zone where the exceptional drought continued.
The status of the drought improved across some of the zone through the month of August. The extreme (D3) drought improved to the severe (D2) category across the far northwest portion of the zone with the exceptional (D4) drought improving to the extreme category over the far southwest portion. The extreme drought remained unchanged elsewhere except over the southeast portion of the zone where the exceptional drought continued.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Utah in 2021Every state in 2021This day in weather historyWarnings in Utah, August 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: 972606, 972607, 972608, 972609, 972610, 972611, 972612.