Strong surface heating resulted in marginal instability and, when paired with residual monsoonal moisture, isolated thunderstorms developed over the higher terrain. As these cells drifted into the valleys they began to collapse and produce severe thunderstorm wind gusts across portions of southwest Colorado.
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The episode as NWS GJT wrote it up.
Strong surface heating resulted in marginal instability and, when paired with residual monsoonal moisture, isolated thunderstorms developed over the higher terrain. As these cells drifted into the valleys they began to collapse and produce severe thunderstorm wind gusts across portions of southwest Colorado.
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 1, 10:34 AM MST, 2 hours 57 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1134 AM MDT Sat Aug 1 2020 .SHORT TERM...(Today through Sunday) Issued at 400 AM MDT Sat Aug 1 2020 A ridge axis at 500mb will remain positioned over far eastern Utah on Saturday afternoon. To the west of this ridge axis, extremely dry air is in place, characterized by PWAT anomalies of -1 to -2 sigma. To the east, including much of western Colorado, atmospheric moisture content will remain near to slightly below normal for the first day of August. As daytime heating commences, another round of orographic convection is likely in the higher terrain by early afternoon. The Colorado ranges will be favored, and mid/upper level winds will support a general southeasterly motion to any showers/storms that do form. Isolated wind gusts upward of 40 mph and perhaps some small hail as large as 0.5 inches will be possible in the southern San Juan range, where storms will have slightly more surface moisture to work with as they dive southeastward toward New Mexico. Convection is expected to quickly diminish after sunset with mainly clear skies overnight. A very similar day is expected on Sunday as the ridge axis remains over central/eastern Utah. Expect showers and some isolated thunderstorms in the higher terrain, again favoring the Colorado ranges and San Juans, with activity diminishing after sunset. Forecast high temperatures will run near the century mark in the Grand Valley, the mid 90s in Montrose and Rifle, and near 90 in Durango. These values are all 8-10 degrees above average for early August. No major changes were made to the short term forecast overnight and forecast guidance is in excellent agreement through the period. .LONG TERM...(Sunday night through Friday) Issued at 400 AM MDT Sat Aug 1 2020 The ridge axis over the southwestern CONUS will shift slightly eastward on Monday and flatten a bit by Tuesday. The net result of this shift will be even drier days for eastern Utah and western Colorado to start next week. Afternoon orographic showers and thunderstorms will be confined mainly to the highest elevations of the Colorado ranges and Continental Divide on Monday...with a completely dry day likely on Tuesday. Afternoon highs will continue to run well above normal given the lack of any monsoonal pushes through this timeframe. The synoptic weather pattern changes a bit from Wednesday through the end of next week. As the ridge of high pressure over the southwest continues to break down on Wednesday, a weak trough is progged to move in along the northern California coast. The combined actions of these two events will help push light southwesterly flow back in over the Four Corners by late Wednesday afternoon. Both the GFS and the ECMWF indicate a fairly robust area of moisture over Arizona and New Mexico at this time. Higher surface dewpoints, greater PWAT values, and favorable flow may not quite make it north of the Four Corners by Wednesday however. As of the 0z model cycle early this morning...Wednesday still looks to end up mainly dry due to this delayed northward push of moisture. This changes by Thursday however, as a strong signal for south-southwesterly flow and moisture transport is apparent in both major global models. PWAT/surface dewpoints climb well above average at this time. Additionally, a subtle shortwave will traverse the base of the broader western trough, providing additional lift and positive vorticity advection to southeast Utah and much of western Colorado on Thursday. As of this morning, Thursday looks to be the most active day in the forecast period. Thunderstorms with heavy rain and the potential for localized flash flooding could be possible if this forecast were to pan out as currently modeled. Active weather will continue on Friday with southwest flow in place, however a push of drier air from the west as modeled in previous cycles may ultimately foil another day of monsoon showers and thunderstorms by then. Forecast confidence remains high through the long term until Thursday. By Friday, differences in exactly how long-lived the monsoonal moisture push will last become apparent, and confidence diminishes quickly from Friday through the coming weekend. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1131 AM MDT Sat Aug 1 2020 Isolated to scattered thunderstorm development is expected through the afternoon and early evening as heating of the day taps into moisture aloft. The main threat to aviation will be the gusty outflow winds which could exceed 40 mph. Confidence not high on timing in forecast due to coverage. Southward drifting storms off the terrain would suggest KDRO has the highest probability of seeing these gusty winds. VFR should prevail over the next 24 hours. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...MAC LONG TERM...MAC AVIATION...TGJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 801 AM MDT Sat Aug 1 2020 COZ001>014-017>023-UTZ022>025-027>029-021415- 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- 801 AM MDT Sat Aug 1 2020 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Isolated showers and thunderstorms are possible over the higher terrain with some brief gusty winds in the San Juans. .DAYS TWO THROUGH SEVEN...Sunday through Friday No hazardous weather is expected at this time. A better push of monsoon moisture is possible by Thursday and Friday. Until then, only isolated afternoon mountain showers are likely. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Grand Junction radar (KGJX), 216 km away, was scanning. The volume nearest the first event began at 20:31 UTC.
1 thunderstorm wind. Local standard time, as filed.
A peak wind gust of 62 mph was measured by the automated weather station at the Durango-La Plata County Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2020Every state in 2020This day in weather historyWarnings in Colorado, August 2020
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: 898368.