An upper level disturbance triggered morning thunderstorms that produced frequent lightning across southwest Colorado.
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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 upper level disturbance triggered morning thunderstorms that produced frequent lightning across 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 May 9, 4:18 AM MST, 1 hour 42 minutes earlier.
Area Forecast Discussion National Weather Service GRAND JUNCTION CO 518 AM MDT Tue May 9 2017 .SHORT TERM...(Today through Wednesday) Issued at 301 AM MDT Tue May 9 2017 Another active weather day in store as the cutoff low continues to influence our weather. Water vapor imagery clearly shows the center of the low to be just south of southwestern Arizona and by this evening it really won't have moved all that much. PWATs and specific humidities remain high over the forecast area and as pieces of energy rotate around the low pressure, we can expect convection to fire once again. All models agree that convection will favor our southern areas from about noon onwards and shift northward through the day following a wave ejected from the parent low. Main concerns will be gusty winds reaching upwards of 40 MPH at times with some pea to dime sized hail. From late afternoon/early evening onwards, a few showers and storms are expected for the San Juans south but an uptick is expected from the central mountains and I-70 corridor northward. While most convection usually dies down after sunset, a deformation zone looks to set up over the Bookcliffs stretching from eastern Utah to just south of Steamboat Springs. Examination of the NAMNEST (3km resolution NAM) model indicates the wave moving up southward and interacting with this deformation zone for the overnight hours into Wednesday morning. If this occurs, some heavy rain is certainly possible and will need to be monitored. The highest peaks will likely see some snow but little to no accumulation expected. By Wednesday, the low will have moved to central New Mexico with some heavier showers continuing along the deformation zone. This area remains favored for much of the day but as the low continues to move east, the intensity should lessen considerably. A few showers and storms are still possible across the CWA but the San Juans and areas south, Durango and Pagosa Springs in particular, look favored as they will be closest to the low and will see the best lift. By midnight, the low will have moved far enough east that most precipitation will end for the CWA as high pressure finally begins to build in. .LONG TERM...(Wednesday night through Monday) Issued at 301 AM MDT Tue May 9 2017 The closed low will slowly move east across the southern Colorado border Wednesday night and onto the High Plains of Oklahoma on Thursday. Shower activity will be focused along the Continental Divide Wednesday night and diminish by early Thursday. A ridge of high pressure will move east across the forecast area on Thursday and Friday bringing a return to warmer temperatures. Residual low level moisture will allow some late day isolated showers and thunderstorms to develop, mainly over mountain locations. Southwest gradient will increase this weekend ahead of a complex storm system over the Pacific Northwest. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) Issued at 517 AM MDT Tue May 9 2017 VFR conditions will continue through 18Z. After that, convection will start to fire causing some showers and thunderstorms to form. VCSH and VCTS looks possible for most TAF sites so will include in TAF. No tempo groups for -TSRA on station as this time however. Convection will fire down south first and then favor the I-70 corridor and areas north from 00Z onwards. Some brief MVFR/IFR possible under any showers or storms that form. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...TGR LONG TERM...MPM AVIATION...TGR
Hazardous Weather Outlook National Weather Service GRAND JUNCTION CO 532 AM MDT Tue May 9 2017 COZ001>014-017>023-UTZ022>025-027>029-101200- 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- 532 AM MDT Tue May 9 2017 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Another day of showers and thunderstorms is expected as a closed low, located just south of Arizona, moves eastward. Showers and storms will fire around noon for our southern areas and shift northward through the day. By late afternoon, showers and storms will have shifted to the I-70 corridor and areas north. The main concern with the storms will be gusty winds, some hail and heavy rain. Some precipitation will continue overnight and into tomorrow. .DAYS TWO THROUGH SEVEN...Wednesday through Monday A few storms and showers will continue into Wednesday but coverage will be much less than seen recently. High pressure then builds in and persists through the weekend. A few stray showers, maybe a storm or two, are possible along the Continental Divide during the period. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Grand Junction radar (KGJX), 194 km away, was scanning. The volume nearest the first event began at 13:01 UTC.
1 lightning. Local standard time, as filed.
Morning thunderstorms produced frequent lightning which ignited numerous tree fires and blasted a tree which fell across electrical lines. Lightning also sparked a structure fire on South Madison Street in Cortez.
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, May 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: 691266.