Low level moisture remained trapped underneath the inversions across northeast Utah which led to the development of dense fog in the Eastern Uinta Basin.
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The episode as NWS GJT wrote it up.
Low level moisture remained trapped underneath the inversions across northeast Utah which led to the development of dense fog in the Eastern Uinta Basin.
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 Jan 1, 4:29 PM MST, 3 hours 31 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 429 PM MST Fri Jan 1 2021 .SHORT TERM...(Tonight through Saturday night) Issued at 207 PM MST Fri Jan 1 2021 Skies were sunny or mostly sunny across much of the region early this afternoon as a positive tilt mid-level ridge moved over the northwest portion of the forecast area. However, the strong inversion over the eastern Uintah basin trapped low stratus over the valley and skies were cloudy over much of the area. Meanwhile, a shallow shortwave trough moving south-southeastward across the southern portion of the forecast area spread clouds over southwest Colorado and the West Elk and Sawatch Mountains of central Colorado. Instability and residual moisture combined with weak lift associated with this disturbance appeared to be generating isolated light snow showers over the higher peaks of the San Juan Mountains according to cooling tops in infrared satellite imagery. Expect this shower activity to dwindle rapidly during the early evening hours as the atmosphere stabilizes and the shortwave passes south of the area. Low level inversions are likely to allow clouds to reform over some valleys, most notably the eastern Uinta basin where patchy fog is likely late tonight. Overnight lows will remain cold and don't expect significant changes from last night. On Saturday, a fast moving low-amplitude mid-level shortwave trough will brush the northern Colorado mountains during the afternoon and evening. Lift associated with this disturbance is expected to bring isolated showers during the afternoon with scattered activity over the Elkhead and Park Mountains in the evening. Accumulations with this system will be light with amounts of 1 to 2 inches expected above 8500 feet. In the wake of the trough showers are expected to diminish during the overnight hours. Elsewhere, clouds will expand across the eastern Uinta basin as temperatures cool while the remainder of the area has partly to mostly clear skies. Meanwhile, models suggest temperatures will trend warmer, but not convinced we will see much change .LONG TERM...(Sunday through Friday) Issued at 207 PM MST Fri Jan 1 2021 The consensus among the latest numerical guidance is for low amplitude ridging to build in through the day on Sunday, keeping a majority of the forecast area dry. However, the 12Z NAM has introduced the slightest of ripples in the northwesterly mid-level flow aloft. Should this materialize, another round of weak upslope snow showers would be possible, mainly in the Elkhead, Park and Gore ranges. Confidence is low at the moment, but did acknowledge the potential by raising PoPs a bit in those ranges. Otherwise, we're looking at a rather seasonable day across the western slope with a partly sunny sky and temperatures within a few degrees of normal. The next wave we are watching crashes into Northern California on Monday which will pump up mid-level heights downstream over eastern Utah and western Colorado. Winds aloft will turn more southwesterly, which will result in weak warm advection and surface temperatures a couple degrees higher than Sunday. By Tuesday morning, the potent wave will have crossed over the Great Basin and will be positioned over the Utah/Colorado border. The 12Z EC is advertising a quick- moving but rather robust system which is accompanied by a strong cold front. The operational GFS continues to insist on closing off the wave into a closed low over Utah or Colorado, but is trending more towards the EC...which is similar to the Canadian. Looking deeper, the WPC ensemble cluster 500mb heights would lend further support to the open wave solution of the EC and Canadian. With the idea that the EC/Canadian are on the right track, the concern is for a more impactful system on Tuesday than you would otherwise think at first glance. Synoptically, the evolution of this shortwave isn't that far off from the one that passed through here and produced snow squalls in northwest Colorado on 22 December 2020. There's a fairly strong signal in the guidance for a combination of positive differential vorticity advection, jet dynamics, 700mb frontogenesis, steep lapse rates and even some nonzero SBCAPE (again favoring northwest Colorado). This potential setup would be an ideal environment for snow squalls and perhaps even a flash freeze. It will still take a few more days to nail down the specifics... and CAM guidance will soon provide more details... but think now is a good time to start messaging the possibility of a more impactful even on Tuesday. Stay tuned. Regardless of what happens on Tuesday, quiet, but colder weather follows on Wednesday with the next system in the pipeline arriving Thursday or Friday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 413 PM MST Fri Jan 1 2021 Expect clearing skies overnight at all terminals with light and variable winds. The exception will be in VEL where low stratus and fog will remain trapped in the valley inversion. LIFR VIS and CIGs will continue through the overnight with fog lifting into stratus late on Saturday morning. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...NL LONG TERM...MDM AVIATION...MAC
Hazardous Weather Outlook National Weather Service Grand Junction CO 528 AM MST Fri Jan 1 2021 COZ001>014-017>023-UTZ022>025-027>029-021230- 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- 528 AM MST Fri Jan 1 2021 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Saturday through Thursday The next chance for any significant precipitation looks to be on Tuesday as a system may bring some snow to the mountains. Otherwise, times of clouds and sun for the next several days. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The national radar mosaic for the moment the first event began.
1 dense fog. Local standard time, as filed.
Dense fog was observed across the Eastern Uinta Basin including at the Vernal Regional Airport as visibility was reduced to less than one quarter of a mile for several hours.
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, January 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: 927874.