Low level moisture trapped across eastern Utah, combined with clear skies and light winds, led to areas of dense fog in some of the northeast and east-central valleys.
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The episode as NWS GJT wrote it up.
Low level moisture trapped across eastern Utah, combined with clear skies and light winds, led to areas of dense fog in some of the northeast and east-central valleys.
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 Dec 18, 10:26 PM MST, 1 hour 34 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1026 PM MST Fri Dec 18 2020 .SHORT TERM...(Tonight through Saturday night) Issued at 209 PM MST Fri Dec 18 2020 The system that brought all the snow has shifted to the east while north to northwesterly flow has set up across the region. Some light snow does linger for favorable facing slopes, especially the northern mountains, but appreciable accumulations look to have ended. Short range models do keep those spotty snowshowers continuing this afternoon and evening so forecast follows suit though coverage will decrease from here on out. Having said that, the models do keep light snow going for the Park Range with the NAM really wanting to keep this precip going through tomorrow and beyond. We've seen this set-up plenty of times in the past with favorable flow for that region so did keep PoPs going there. Nothing out of the ordinary for you folks up north. The remainder of the CWA is now contending with low clouds, especially in some of the valleys, where banks of overcast skies have set up...we're looking at you Grand Valley. Satellite does show some eroding of this, and other, cloud banks but don't expect it to burn off as it's so late in the day and the sun angle is so low. Went ahead and bumped high temps down a few degrees as the moisture trapped beneath the clouds and lack of sun will keep things chilly. The next question then becomes fog and with the precip we received, expect some patchy fog for Vernal, Craig, the Grand Valley, Gunnison and possibly between Durango and Pagosa Springs. Overnight and into tomorrow, a weak transitory ridge will move through keeping northwesterly winds in place across the region with some off and on snow continues for the northern mountains. By the afternoon, a very weak, quick moving shortwave will brush the CO/WY border and provide a bit of an uptick of snow for the northern mountains late Saturday afternoon into the evening hours. Moisture is hard to come by so 2 to 3 inches for the Park Range looks feasible when all is said and done. The rest of the CWA will remain dry with increased cloud cover...more up north versus down south...and seasonal temperatures. .LONG TERM...(Sunday through Friday) Issued at 209 PM MST Fri Dec 18 2020 Trailing northwest flow on Sunday behind a departing shortwave trough will result in some continued light snow over the Park Range due to favored NW orographics and temperatures remaining in the dendritic growth zone. Little accumulation is expected. A ridge of high pressure will build over California out west and move over the region by Monday, providing for mostly sunny skies and temperatures rebounding towards near to a few degrees above normal values through Tuesday. This will be short-lived as a low pressure trough moves into the Pacific Northwest and barrels through the Intermountain West and Northern Rockies states, before moving onto the Plains and Midwest by Wednesday morning. The Western Slope will see the southern end of this system with the northern and central Colorado mountains favored for snowfall mainly during the Tuesday late afternoon and evening timeframe. Snow looks to continue over these areas through Wednesday morning before coming to an end as the system gains strength across the Midwest Wednesday afternoon through Thursday. The models still remain inconsistent on the strength and timing of this system as previous runs of the ECMWF were a bit weaker and further north with it. One thing that does remain consistent is the much colder air mass that will encompass the region behind it's cold front and trough passage Tuesday night into Wednesday morning. Temperatures look to remain below normal Wednesday through the end of the week. Drier conditions will return along with colder air late Wednesday morning into the afternoon and for the rest of the week through Christmas Day as a ridge of high pressure amplifies across the western CONUS. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1023 PM MST Fri Dec 18 2020 As skies clear out from the northwest, expect improving conditions to VFR by early evening and overnight with scattered cloud cover aloft at times. Some fog has started to develop in snow-covered valleys...but the presence of higher clouds may prevent this from being widespread. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...TGR LONG TERM...MDA AVIATION...TGJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 401 AM MST Fri Dec 18 2020 COZ001>014-017>023-UTZ022>025-027>029-191115- 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- 401 AM MST Fri Dec 18 2020 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Snow continues across western Colorado today, then diminishes tonight. Accumulations of 3 to 7 inches are expected across the Elkhead, Park and Flat Top Mountains, the Grand Mesa, and the West Elk, Sawatch and northwest San Juan Mountains. Amounts in the valleys will generally range from 1 to 2 inches. .DAYS TWO THROUGH SEVEN...Saturday through Thursday A weak disturbance passes over the Elkhead and Park Mountains Saturday, but accumulations are expected to be light. The next chance for snow comes Tuesday into Wednesday with the northern mountains again favored. Early indications are that snowfall generated by this system will also be light. .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 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.
Dense fog was observed across the Grant Flat and Arches region including at the Canyonlands Field 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 2020Every state in 2020This day in weather historyWarnings in Utah, December 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: 925781, 925782.