Trapped low level moisture led to areas of dense fog in the Eastern Uinta Basin.
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The episode as NWS GJT wrote it up.
Trapped low level moisture led to areas 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 Dec 6, 10:40 PM MST, 3 hours 50 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1040 PM MST Fri Dec 6 2019 .SHORT TERM...(Tonight through Saturday night) Issued at 223 PM MST Fri Dec 6 2019 Quiet and dry weather will continue this afternoon, as the ridge of high pressure moves overhead. A deck of high clouds will continue to stream across the region this evening, with lower clouds lingering across the north. Some clearing is likely tonight, while winds aloft transition to west-southwest flow. Low level clouds and fog will likely develop again across northeastern Utah and western Colorado Saturday morning. Light winds at the surface combined with lingering low level moisture will support fog forming across the Gunnison and Yampa Valleys, portions of the Grand Valley, and near the Uinta Basin. Patchy areas of fog will quickly clear after sunrise; however, other regions with a more consistent stratus deck aloft (such as Gunnison and Vernal) may experience poor visibilities and low cloud ceilings persisting into afternoon hours. Expect winds to shift towards the west Saturday afternoon, as upper level flow turns zonal ahead of the next system. Zonal flow accompanied with increased winds aloft will briefly improve mixing at low levels for most of western Colorado and eastern Utah. Areas with decent mixing will result in slightly warmer temperatures and could see stronger winds reaching the surface. Mixing should also help conditions improve across areas with lingering low level clouds and morning fog. Otherwise, weather conditions will remain dry across the region into Saturday evening, however cloud clover will begin to spread across the region ahead of the next system. Chances for precipitation also increase late Saturday night, mainly over higher terrain, while the rest of the region will experience mild overnight lows due to the insulation from a blanket of cloud cover. .LONG TERM...(Sunday through Friday) Issued at 223 PM MST Fri Dec 6 2019 Precipitation will break out over much of the higher terrain of eastern Utah and western Colorado early on Sunday morning. The trough responsible for the unsettled weather is not particularly strong, but it will make up for this with a broad shield of moisture and favorable westerly upslope flow through the day on Sunday. A diffuse frontal boundary does pass east through the western slope on Sunday afternoon as well, with 700mb temperatures dropping 2-4 degrees across the board by the end of the main event on Sunday evening. This will help snow ratios, especially in the central and northern mountains. Latest QPF guidance in the 12z forecast cycle today showed a slight uptick in precipitation totals, with snow totals possibly exceeding 6 inches in the Park, Flat Top, Gore and Sawatch ranges. Farther south in the Elks and San Juans, close to 1" of liquid is forecast by some models...which could result in nearly a foot of snow in favored westerly and northwesterly slopes. Lower elevations are a bit more tricky, as snow levels and warm air in the valleys will play a role in Precipitation Type early in the event. If enough cold air filters in on Sunday afternoon, an inch or so will be possible in places like Craig, Rifle and Montrose, with 1-3 inches in Steamboat (town), Vail, and Gunnison. The US160 corridor is a particularly challenging forecast, as the San Juan Mountains may block the progress of much of the colder air from the north. Durango could easily see 0" in this case, however a slushy inch or so in the grass is also possible if colder air makes it in before precipitation ends Sunday evening. The trough axis with this system passes east of the Continental Divide by early Monday morning with flow turning northwesterly over eastern Utah and western Colorado. A shallow stream of moisture will remain in place over the northern Colorado mountains in this northwest flow pattern from Monday through Tuesday morning. Favorable upslope flow will result in additional snow accumulations in the northern Parks and Elkhead mountains, however model consistency has not been high in this timeframe. Things finally dry and clear out on Tuesday evening up north as a ridge builds in over the Four Corners for Wednesday. Both the ECMWF and GFS indicate a weak, dry trough moving through on Thursday resulting in a mainly cloudy day. The next opportunity for precipitation will arrive by Friday morning as a fast Pacific jet moves inland and into the Great Basin. Both the ECMWF and GFS support the idea of unsettled weather from Friday into Saturday however specific details with this system will have to wait for better model consistency on both temperatures and the position of the best moisture stream. Overall, forecast confidence is moderate throughout the long term. Winter weather headlines will likely be needed in the mountains for the storm arriving on Sunday morning, and will be addressed in forthcoming forecast packages. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1038 PM MST Fri Dec 6 2019 Fluid stratus deck up north look to mainly impact the Uinta Basin with ILS/MVFR cigs. So far conditions are mixed enough to limit the formation of thicker fog. Confidence not extremely high for fog or stratus formation with high cloudiness drifting through overnight so no mention in current TAFs. VFR should continue over the next 24 hours most areas. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...ERW LONG TERM...MAC AVIATION...TGJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 431 AM MST Fri Dec 6 2019 COZ001>014-017>023-UTZ022>025-027>029-071145- 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- 431 AM MST Fri Dec 6 2019 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 A storm system is forecast to arrive in our region by Sunday bringing a serveral inches of snow to the high country by Monday evening. .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 2019Every state in 2019This day in weather historyWarnings in Utah, December 2019
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: 861326.