Low-level moisture remained trapped under strong valley inversions and resulted in the formation of dense fog across portions of the central and upper Yampa River Basins.
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The episode as NWS GJT wrote it up.
Low-level moisture remained trapped under strong valley inversions and resulted in the formation of dense fog across portions of the central and upper Yampa River Basins.
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 Feb 20, 3:34 AM MST, 1 hour 26 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 334 AM MST Mon Feb 20 2017 .SHORT TERM...(Today through Tuesday) Issued at 334 AM MST Mon Feb 20 2017 Low clouds and scattered morning showers will gradually give way to clearing conditions by this afternoon. The clearing will be short-lived as we see more mid and high level clouds spread back over the region with fast WSW flow setting up aloft. The upper jet aligned to bring another prolonger atmospheric river event to portions of the western U.S. with bulk of deep moisture sliding to our north with the jet aligned from northern California NE to eastern Wyoming by Tuesday. What does this all mean for us? Looks like mild conditions will continue for a few more days with isolated to scattered showers favoring the high country through midweek. The jet eventually drops far enough south to drive better forcing into our area just outside of this short-term packaged. Temperatures will be 5 to 10 degrees above seasonal normals today and Tuesday with mild overnight lows expected with increasing blanket of mid/high level cloud cover. .LONG TERM...(Tuesday night through Sunday) Issued at 334 AM MST Mon Feb 20 2017 An increasingly moist zonal flow will develop as a weak baroclinic zone sets up across the northern half of the forecast area on Tuesday night and Wednesday. This feature has grown stronger with each successive run and could see some light to moderate accumulations Tuesday night through Wednesday, especially over the northern mountains. After a brief lull, a colder and more active weather pattern sets up for the region. A better organized shortwave will drop into the Great Basin on Wednesday night and move across the area on Thursday bringing another round of snow to the mountains and rain/snow to the lower elevations Wednesday night into Friday. Moist zonal flow will keep mountain snow shower activity continuing on Saturday as another wave moves across the Great Basin and brings another round of precipitation on Saturday night into Sunday, with the best focus over the southern half of the forecast area. After seasonable temperatures on Wednesday, expect seasonably cold temperatures Thursday through the weekend. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) Issued at 334 AM MST Mon Feb 20 2017 Showers and lingering low clouds will gradually dissipate this morning with areas of IFR/MVFR CIGS and VSBYS breaking out by 16Z. ILS CIGS will hang around through midday with VFR conditions then settling back in at all sites by 21Z. Patchy valley fog will bring off by late this morning, although another round of valley fog possible again tonight, possibly impacting KVEL east to KSBS. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...JDC LONG TERM...MPM AVIATION...JDC
Hazardous Weather Outlook National Weather Service Grand Junction CO 444 AM MST Mon Feb 20 2017 COZ001>014-017>023-UTZ022>025-027>029-211300- 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- 444 AM MST Mon Feb 20 2017 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Scattered snow showers will linger over the mountains this morning with patchy valley fog restricting visibility to under 3 miles at times. Showers and fog dissipate by midday with drier weather moving in this afternoon and evening. Cloud cover increases again after midnight as another Pacific Storm moves onshore. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday There is a chance for valley rain showers and mountains snow showers each afternoon and evening as a series of moist Pacific storms pass through the region. Colder air may flip the valleys over to all snow by Thursday. Moderate to heavy snow accumulations will be possible late this week and into the weekend. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected today or tonight, however spotters are encouraged to report snowfall amounts to the National Weather Service in Grand Junction.
The national radar mosaic for the moment the first event began.
2 dense fog. Local standard time, as filed.
Dense fog occurred across portions of the upper Yampa River Basin as visibilities dropped down to a quarter mile or less.
Dense fog occurred across portions of the central Yampa River Basin as visibilities dropped down to a quarter mile or less.
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, February 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: 685901, 685900.