A cold front dropped southward across Wyoming and brought high winds to northern Johnson County, Wyoming. The maximum wind gusts reported were 68 mph at the Johnson County airport and 63 mph at Kearney Divide along Interstate 90.
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The episode as NWS RIW wrote it up.
A cold front dropped southward across Wyoming and brought high winds to northern Johnson County, Wyoming. The maximum wind gusts reported were 68 mph at the Johnson County airport and 63 mph at Kearney Divide along Interstate 90.
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 Riverton, WY wrote its last area forecast discussion before the first event at Dec 1, 1:53 AM MST, 5 hours 55 minutes earlier.
Area Forecast Discussion...AMENDED National Weather Service Riverton WY 153 AM MST Tue Dec 1 2020 .SHORT TERM...Today through Thursday night A Pacific cold front and trough continues to move across the area, bringing snow showers and strong winds to some areas. We had a 45 mph wind gust at our office with gusts to 50 mph at Buffalo. Snow showers also continue to move through the area, although amounts have been fairly light so far. The story for today will be a cooler and blustery day for most locations. The strongest winds are still expected in areas favored by north to northwest flow and cold advection, like the Bighorn Basin, northern Johnson County and even the Wind River Basin. The 700 millibar winds do not look quite high enough for high winds. A special weather statement remains in effect for northern Johnson County for this criteria. As for snow showers, with cyclonic curvature over the area and unstable north to northwesterly flow, there will continue to be some around today. This will be especially true in eastern portions of the area, with the best chance in the western Bighorn Range with the upslope component as well as Casper Mountain. There is not a lot of moisture to work with, so amounts should remain on the light side. Only a few inches are expected in and near the mountains where a few inches will be possible and possibly where banding might set up. A second round of showers will be possible tonight into Wednesday morning, as a second piece of energy drops southward into the area from the Canadian Prairie provinces. But again, given the origin of the air mass, there will be little moisture to work with. Most of the shower activity will remain east of the Divide, down to eastern Sweetwater County. A few spots may pick up locally higher amounts if banding sets up, but pinpointing where this occurs is a bit difficult this far out. Western portions should remain far enough west to remain largely dry. These showers should end Wednesday afternoon, as the energy pushes south of the area. Ridging then folds over the area for Wednesday night into Thursday and brings dry and chilly weather with light winds. This will likely lead to inversions setting up in the basins and valleys across most of the area. Still some question as to how cold temperatures can get, since snow cover will be spotty. We did keep temperatures below guidance given this pattern. .LONG TERM...Friday through Monday The upper high that has been progged for the last several model runs will continue to maintain its hold over the PACNW/Northern Rockies Friday. Below normal temperatures remain in the forecast, due to inversions keeping the cold air trapped in the valleys and basins. Fog will remain a possibility in the western valleys Friday night/Saturday morning, but confidence has waned in any fog lasting for more than 2 days at this point (Thursday & Friday mornings). The upper high will keep conditions dry, with light winds and mostly clear skies through the weekend. Models have begun to prog a system weakening, as it runs into the ridge. This system will have no impact to the Cowboy State, but could break down the ridge and be a precursor for a more zonal flow pattern next week. && .AVIATION...For the 12Z TAFS through 12Z Wednesday West of the Continental Divide...KBPI/KJAC/KPNA/KRKS Terminals Expect VFR conditions across the terminals during the TAF period. Gusty winds are likely for all locations, except KJAC, where there may be gusts to around 30 knots. Winds should diminish between 02Z-06Z across the terminals. East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals Expect VFR conditions for all terminals, with the exception of KCPR until about 13Z, due to some forecasted light snow and lowered visibility. MVFR or IFR conditions can be expected there. Otherwise, VCSH may prevail through the morning hours, lingering at KCPR through the day. The other weather of note is to be the winds. Winds may gust to between 20-30 knots across the Wind River and Bighorn basins. && .FIRE WEATHER... Today will be a blustery and cooler day across the area. Snow showers will be scattered east of the Divide, but amounts should be light except in the mountains. Strong winds are likely in portions of the Bighorn Basin and especially northern Johnson County. Additional snow showers are possible tonight into Wednesday morning. Relative humidity will remain above critical levels. Mixing and smoke dispersal will be generally poor in the west and good east of the Divide. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...Hattings LONG TERM...LaVoie AVIATION...Clayton FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 157 AM MST Tue Dec 1 2020 WYZ001>020-022>030-020900- Yellowstone National Park-Absaroka Mountains-Cody Foothills- North Big Horn Basin-Southwest Big Horn Basin- Southeast Big Horn Basin-Owl Creek and Bridger Mountains- Bighorn Mountains West-Bighorn Mountains Southeast- Northeast Johnson County-Southeast Johnson County- Teton and Gros Ventre Mountains-Jackson Hole- Wind River Mountains West-Wind River Mountains East- Upper Wind River Basin-Wind River Basin-Lander Foothills- Green Mountains and Rattlesnake Range- Natrona County Lower Elevations-Casper Mountain-Star Valley- Salt River and Wyoming Ranges-Upper Green River Basin Foothills- Upper Green River Basin-South Lincoln County- Rock Springs and Green River-Flaming Gorge-East Sweetwater County- 157 AM MST Tue Dec 1 2020 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Strong winds likely for many areas, especially the Big Horn Basin and northern Johnson County. Snow showers may bring locally slick roads, mainly East of the Divide. .DAYS TWO THROUGH SEVEN...Wednesday through Sunday. The probability of widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions, according to standard operating procedures. TEAM RIVERTON
Special Weather Statement National Weather Service Riverton WY 158 AM MST Tue Dec 1 2020 WYZ010-020000- Northeast Johnson County- Including the city of Buffalo 158 AM MST Tue Dec 1 2020 This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Northwest winds 25 to 35 mph with gusts to 50 and 55 mph. * WHERE...Northern Johnson County including the Buffalo area. * WHEN...Through this afternoon. * IMPACTS...Mainly to transportation including along Interstates 25 and 90. There will be control issues especially for light and high profile vehicles, including campers and tractor trailers. * ADDITIONAL DETAILS...Please keep two hands on your steering wheel in case of a sudden, strong wind gust.
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2020Every state in 2020This day in weather historyWarnings in Wyoming, 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: 923881.