Increasing subtropical moisture that flowed up into western Colorado produced a thunderstorm with a little rotation.
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The episode as NWS GJT wrote it up.
Increasing subtropical moisture that flowed up into western Colorado produced a thunderstorm with a little rotation.
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 22, 10:41 AM MST, 2 hours 43 minutes earlier.
Area Forecast Discussion National Weather Service GRAND JUNCTION CO 1141 AM MDT Tue Aug 22 2017 .SHORT TERM...(Today through Wednesday) Issued at 353 AM MDT Tue Aug 22 2017 High pressure remained overhead early this morning while low pressure continued to circulate over southern California early this morning. Clouds lingered over the southern half of the forecast area where difluence aloft prevalent. As mentioned in previous discussions, models carry a shortwave trough northward along the eastern edge of the SoCal low. This disturbance will move across southeast Utah and southwest Colorado this morning bringing increased clouds and light showers before noon. Thunderstorms will likely hold off until the latter part of the morning. The disturbance continues to lift northward, pushing over the central portion of the forecast area this afternoon which will combine with daytime heating to generate more showers and thunderstorms than seen over the past several days. Soundings from around the area indicated an increase in moisture and the 00Z/Tues KGJT sounding recorded 0.75 inches of liquid in the airmass. Therefore, expect some of these storms will become heavy rain producers. The shortwave moves into the north tonight which should sustain showers and thunderstorms later into the evening, especially across northwest Colorado and northeast Utah. Some lighter nocturnal activity is possible after midnight. This disturbance remains a player in weather conditions Wednesday as it moves slowly east northeastward over the north during the day. Consequently, expect showers and thunderstorms will get an earlier start there with greater coverage during the afternoon. Meanwhile, to the south residual moisture is expected to fuel another round of diurnally driven showers and thunderstorms, mainly over the higher terrain. High temperatures will be cooler today in response to increased cloud cover and showers/thunderstorms, most noticeably across the south. In the wake of the shortwave trough described above, highs in the south will rebound to near normal. In contrast, highs across the north will be suppressed Wednesday as the disturbance moves overhead. .LONG TERM...(Wednesday night through Monday) Issued at 353 AM MDT Tue Aug 22 2017 Upper level low in the Gulf of Alaska finally making a push southeastward toward the Lower 48 on Wednesday and Thursday. This will allow the southern closed low over SoCal to dissolve into high pressure over the southern US. A weather disturbance progged to push through eastern UT and western CO Wednesday night into Thursday morning potentially bringing some nocturnal showers and thunderstorms. Drier conditions are expected to develop beginning Friday as high pressure amplifies over the Southwest and filters drier air into the region from the northwest. Temperatures will run a few degrees above normal over the weekend and into early next week. Afternoon convection should remain focused over the highest terrain with valleys remaining dry. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1141 AM MDT Tue Aug 22 2017 A disturbance will work through the region today and, when combined with daytime heating and increased moisture, lead to scattered to numerous showers and thunderstorms this afternoon and evening. Storms will be in the vicinity of and potentially impact TAF sites along the Divide and south of I-70, particularly KTEX and KDRO. ILS breakpoints will be reached at times and mountains will become obscured. A few nocturnal showers will persist overnight as the disturbance lifts north, resulting in another round of afternoon convection on Wednesday. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...NL LONG TERM...JAM AVIATION...TGJT
Hazardous Weather Outlook National Weather Service GRAND JUNCTION CO 430 AM MDT Tue Aug 22 2017 COZ001>014-017>023-UTZ022>025-027>029-231030- 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- 430 AM MDT Tue Aug 22 2017 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Scattered thunderstorms will develop over the mountains today with some cells moving over adjacent valleys during the latter part of the afternoon and into the evening. The main threat from these storms is localized heavy rain, lightning and outflow winds to 40 MPH. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Wednesday and Thursday...Scattered to numerous diurnally driven showers and thunderstorms will continue as moisture lingers. Friday through Monday...Diurnal thunderstorms will decrease in coverage as drier air filters over the area. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1040 AM MDT TUE AUG 22 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0600 PM HEAVY RAIN 2 ESE HESPERUS 37.26N 107.99W
08/21/2017 M1.75 INCH LA PLATA CO TRAINED SPOTTER
THE DURATION OF THE HEAVY RAIN EVENT WAS 3
HOURS.
&&
MMSThe Grand Junction radar (KGJX), 81 km away, was scanning. The volume nearest the first event began at 20:23 UTC.
1 funnel cloud. Local standard time, as filed.
A short-lived funnel cloud was observed by a traveler who was driving south on Highway 139.
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: 708527.