A cold front swept across Wyoming and brought snow to some areas. Most of the snow was light to moderate.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS RIW wrote it up.
A cold front swept across Wyoming and brought snow to some areas. Most of the snow was light to moderate. However, in the Lander foothills upslope flow helped to enhance snowfall rates and brought locally heavy snow. Amounts of 5 to 9 inches were common around Lander, with 8.3 inches measured at the Lander airport. In addition, locally high winds occurred ahead of the front in the wind prone areas near Clark in Park County. At the wind sensor 5 miles west of Clark, there was around a 3 hour period of high wind including a maximum wind gust of 98 mph.
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 19, 11:08 PM MST, 1 hour 28 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1108 PM MST Tue Dec 19 2017 .SHORT TERM...Tonight through Friday About 35 years ago, the late, great Tom Petty had a hit song called "Change of Heart." Well, if the short term discussion had a title it would be "Change of Pattern." Mainly, the persistent zonal flow that has kept the area fairly mild over through much of December finally looks like it is changing and some real winter will be arriving. And ironically, right around the winter solstice, which is at 9:26 on Thursday. As a result, we have several concerns over the next few days, running the gambit from wind to snow to cold. Temperatures should remain mild for the next 24 hours, maybe a bit warmer Wednesday in many areas aided by the southwest flow ahead of the advancing Canadian cold front. This will also tighten the pressure gradient ahead of the advancing front and bring windy conditions, especially to the favored areas like from Rock Springs through Natrona County and in the Lee of the Absarokas. As for potential high wind highlights, the set up is not the greatest in the world. There could be a few high wind gusts at places like Camp Creek and around Clark. But seeing how a 60 mph wind gust near Clark this time of year is called Wednesday and there is nothing around Camp Creek expect deer, we will stick with the Special Weather Statement which we feel was the right decision. Snow will begin to spread into the west late tonight but the bulk should hold off until Wednesday. As for highlights in this area, anything would be limited to Yellowstone and the Tetons and even here it is borderline since moderate snow would mean mainly dollar signs in the Tetons and there are very few people in Yellowstone in the winter.We did slow down the progression of the snow spreading East of the Divide however since the models have slowed. We removed the Big Horn rain forest effect in the morning. There is a small chance some light precipitation could spread east toward sunset but a vast majority of the day should be dry. The Canadian Front will spread east of the Divide at night and spread some snow into those areas. As is the case with most Canadian fronts, it has limited moisture to work with. In addition, the snow would not last that long. However, there could be a period of heavy snow as the front moves in, especially from south of the Owl Creek range and into Sweetwater County. The culprit for this will be a right rear/ front left jet couplet that could really enhance upward motion, mainly from around 8 pm to around 5 am Wednesday night. Most of the steady snow should end Thursday morning, although some clouds and flurries may linger a bit longer. In addition, it will turn windy in some areas. The main area for concern for this would be from the northern Big Horn Basin into northern Johnson County with the strong cold advection and north to northwest flow. Again, it looks borderline since 700 millibar winds are borderline. Since this would not occur until Wednesday evening, we still have time to decide on any potential highlights. Right now, it looks like mainly winter weather advisories although we could see a warning for a place like Sweetwater County due to the impacts on travel with Interstate 80. The main story after that will be the cold temperatures. Temperatures in many areas will likely fall through the day on Thursday as colder air moves in, with some areas in the single digits by evening. On the Canadian front's heels, will be another cold front. The difference being this one is an Arctic Front, with even colder air. The models do have some differences with timing this front though, with the NAM about 6 to 12 hours faster than the GFS. For now, we made few changes. This will be the front that will introduce the really cold air that may make Santa have to put on a few extra layers when he delivers gifts on Christmas Eve. .LONG TERM...Friday night through Tuesday night The arctic front and precipitation will be ongoing at the beginning of the forecast period. However, models have slowed the progression of the colder H7 sub -20C temps. While the GFS has -20C temps as far south as the Red Desert by 12Z Saturday, the ECMWF is about 6 hrs slower and just beginning to enter Fremont and Natrona counties at that time. Snow will be widespread Friday night and favor upslope locations like Lander and Casper. General amounts of 2-4", 3-6" still look favorable with snow ending Saturday afternoon. Even though there is little difference with the pattern depiction, the GFS quickly modifies H7 temps into the teens by 12Z Sun, while the ECMWF keeps the pool of -20C temps over the region through 00Z Monday. Models solutions become split at this point, but regardless of whether a ridge builds over the area or the region comes under the influence of the southern branch of the jet, H7 temps are expected to warm Monday and Tuesday. Regardless, temperatures should moderate little with the arctic air in place and fresh snow cover. Apart from the Cody Foothills, I-80 corridor and NE WY, surface inversions look to remain in place early next week. && .AVIATION...06Z Issuance West of the Continental Divide...KJAC, KBPI, KPNA and KRKS At KJAC airport periods of snow will occur overnight through 00Z Thursday. MVFR will prevail with possible IFR conditions at times. Conditions improve at KJAC airport after 00Z Thursday. VFR conditions will prevail at KPNA, KBPI, and KRKS through 03Z Thursday. A cold front moves into western WY after 18Z and scattered snow showers will occur at the lower elevations through 01Z. KRKS will see a cold front push around 00Z with scattered snow showers in the vicinity, then snow will prevail at KRKS after 03Z Thursday with IFR conditions. East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL VFR conditions will prevail through 00Z Thursday. A cold front will push into northern WY after 20Z and move southward into central around 00Z Thursday. Areas of snow will create MVFR cigs and vsbys in northern WY after 23Z and continue through 06Z Thurs. The snow will begin after 01Z in central WY with MVFR/IFR conditions prevailing by 03Z Thursday. && .FIRE WEATHER... Other than some snow showers across the northwest, expect mainly dry weather through tonight. Snow will continue across much of the west Wednesday but will hold off East of the Divide until Wednesday evening. Much of tonight and Wednesday will remain mild. A gusty breeze will develop at times and windy conditions, including some strong winds, will develop across the southwestern Wind Corridor and in the Lee of the Absarokas. Mixing and smoke dispersal will range from poor in the basins to good in the normally windier locations. A strong cold front will move across the state Wednesday night and bring a period of snow along with much colder temperatures for Thursday through the Christmas weekend. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Hattings LONG TERM...LaVoie AVIATION...AR FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 256 AM MST Tue Dec 19 2017 WYZ001>020-022>030-201200- 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- 256 AM MST Tue Dec 19 2017 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Strong wind possible across the Cody Foothills and southern wind corridor from Jeffrey City to Casper. .DAYS TWO THROUGH SEVEN...Wednesday through Christmas Day. Wednesday through Thursday morning...Another storm system will spread snow and much colder air southeast across the area. Friday and Saturday...An arctic cold front and storm system will spread snow and bitter cold air across the area. .SPOTTER INFORMATION STATEMENT... Spotters are urged to report wind gusts over 50 mph. Thank you.
The national radar mosaic for the moment the first event began.
1 high wind, 1 winter storm. Local standard time, as filed.
Several wind gusts over 58 mph were recorded 5 miles west of Clark, including a maximum gust of 98 mph.
The observer at the Lander airport measured 8.3 inches of new snow. Around Lander, 5 to 9 inches of snow was common.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2017Every state in 2017This day in weather historyWarnings in Wyoming, December 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: 728276, 728278.