A Pacific weather system moved across western and central Wyoming and brought locally heavy snow and high winds. In the western mountains, the heaviest snow fell in the Tetons where 20 inches of new snow fell at Grand Targhee.
Every event with a place to put it; 6 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 Pacific weather system moved across western and central Wyoming and brought locally heavy snow and high winds. In the western mountains, the heaviest snow fell in the Tetons where 20 inches of new snow fell at Grand Targhee. The heaviest snow in the lower elevations occurred at Alpine where 10 inches of snow fell. In areas East of the Divide, the heaviest snow fell near Thermopolis where up to a foot of snow fell. Elsewhere, snowfall was lighter. However, in some areas snow combined with wind gusts over 50 mph the bring near zero visibility. The caused the closure of roads in Johnson County for several hours. Other roads were closed in portions of Natrona, Hot Springs and Fremont Counties. Strong winds also occurred ahead of the system in the Cody Foothills, where a wind gust of 81 mph occurred the south of Clark. The winds extended into Cody itself where the Cody airport had a wind gust to 58 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 29, 10:22 AM MST, 1 hour 24 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1022 AM MST Sat Dec 29 2018 .SHORT TERM...Today through Monday night Given the multiple hazards and different effects, we will split the discussion between West and East of the Divide today. West of the Divide...The main concern here is snow. There will be a bit of isentropic lift in the area today so mainly light snow will be ongoing in many areas although amounts should remain relatively light through this evening. Heavier snow will begin later tonight, especially after around 3 am or so as the cold front and trough axis swing through. This will have a major assist with some upper level dynamics in the form of a left front / rear rear quadrant jet couplet moving through the area. Most of the models are in decent agreement in having the heaviest and steadiest snow between around 3 am to early afternoon on Sunday when 1 inch an hour snowfall rates will be possible. Lighter snow will continue after that through the rest of the afternoon and into the night as well. With 700 millibar winds approaching 45 knots, winds will be quite strong at times, especially across the exposed areas. With the cold temperatures and rather powdery consistency of the snow, there will be a decent amount of blowing and drifting snow possible in some areas as well. As for the million dollar question, what about the highlights. For the most part, most amounts look to remain in the advisory range. The exception would be across the Tetons where there could be some warning level amounts. Most of these would probably be above pass level though. Since there is still time, we will let the day shift make the final call on any highlights. High pressure then builds in for Monday with a gradually clearing sky. There is a good chance inversions could set up in the deeper valleys Monday with the fresh snowfall and Monday could get very cold, possibly the coldest night of the year by Monday night. East of the Divide...We have a plethora of concerns here. In a few areas, the fog monster has crawled out of this lair early this morning. However, this fog in patchy with a capital P. For now, we will leave it out of the forecast since a lot may be gone by daybreak. We will start with wind. All the models indicate some 50 to 60 knot 700 millibar winds in the lee of the Absarokas tonight with a bit of a mountain top inversion. With the good chance of high winds, especially in the vicinity of Clark, we will hoist a high wind watch starting this evening. It could also turn quite blustery in areas like Sweetwater County and from the Red Desert through Casper. In these areas though, either 700 millibar winds are not strong enough or from the wrong direction for any wind highlights. There could be a high wind gust at the high altitude RAWS sites like Camp Creek, but since this would only effect deer this time of year, impacts would be close to zero. There could also be some rather strong winds in areas favored by northwest flow and strong cold advection on Sunday, areas like northern Johnson County and the Wind River Basin. At this time, it looks to fall short of high wind though. It will have some effects with the snow as well, more on that in the snow section. Strong winds should end by Monday with mainly light winds that day. The next concern is snow. There could be some light snow in northern areas today. Models are showing some weak lift across the northern Big Horn Basin and the Bighorn mountains this afternoon and early this evening. Moisture is lacking though so any accumulations would be fairly light. We added some slight to chance POPs in that area as a result. This should end by this evening. Most of the tonight should be largely dry as well. Snow will then spread from north to south starting Sunday morning. There are some concerns here though. The models do have some differences. The European model is by far the wettest model with a weak 500 millibar low moving over the northern portions of the state. The NAM and GFS are much drier but even they disagree a bit on the exact placement of the heaviest snow. All models do favor eastern portions of the area though. The European does tend have a wet bias though. We still have time to decide on any upgrades for highlights though. The watch looks good for the areas with the most impacts though, since snow and the aforementioned strong wind may cause some problems. The heaviest snow looks to fall Sunday night, especially during the evening hours. The European is also slower, lingering steadier snow through the day while the other models have only flurries. For now, we made only minor changes to continuity with the uncertainty since we still have time to decide here. The third concern is cold temperatures, possibly the coldest of the year. There are some uncertainties here as well. Mainly, how much snow will fall. If the American models are correct, there may not be a lot of fresh snow and this could limit albedo somewhat. However, they do have a clearing sky and this could help with the cooling and the fresh cold air mass. The European also lingers clouds longer though. Nevertheless, we could be looking at the coldest night of the winter so far for many areas on New Year's Eve. .LONG TERM...Tuesday through Saturday After a very active short term, the long term looks to be relatively quiet with a warming trend as the northerly flow on Tuesday becomes westerly by Thursday/Friday. The biggest challenge in the long-term will be how quickly the trapped basins/valleys warm up after the coldest air of this winter settles into the Cowboy State Monday. Will undercut guidance a bit in typical trapped basin/valleys, but closer to guidance in the mountains and well-mixed areas in typical wind corridors. Also the models are hinting at some strong gap flow developing in the Cody Foothills Wednesday night into Thursday morning as a strong temperature gradient sets up from the Yellowstone Plateau into the Cody Foothills. The next decent chance of precipitation looks to hold off until next weekend with a potential Pacific trough pulling into the West. Will keep Saturday dry for now, as models vary in timing/track of trough, and most guidance does not spread precipitation into the area until next Saturday night/Sunday. && .AVIATION...18Z Issuance East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminal VFR conditions will prevail through 06z Sunday. Surface west to southwest winds of 30-40 knots vicinity KCPR-KRKS through the day today, decreasing slightly after 00Z Sunday. Local MVFR ceilings in light snow or flurries may develop across the eastern Big Horn Basin Saturday afternoon, mainly vicinity and east of a KPOY-KGEY line, with partial mountain obscurations over the Bighorn Range. Ceilings should improve in this area Saturday evening. Ridgetop west wind have already increased this morning, with low level wind shear along the east slopes of the Continental Divide, vicinity KCOD- KDUB. This will continue tonight into Sunday, as these winds increase further south toward KLND. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Areas of MVFR light snow and mountain obscurations will continue vicinity and and north of a KAFO-KDUB line. To the south, the main hazard will be increasing west wind along the Interstate 80 corridor and KRKS with surface west wind 20-30 kts prevailing in the afternoon. Snow and areas of LLWS will increase across the west 06z-12z Sunday ahead of an approaching cold front. Widespread MVFR conditions, areas of IFR ceilings are expected vicinity and north of a KEMM-KPNA line by 12z Sunday. && .FIRE WEATHER... A weather system will bring light snow to western Wyoming today with steadier and heavy snow moving in tonight, especially after midnight. Other then some possible light snow across the northern Big Horn Basin, expect mainly dry conditions East of the Divide today. Strong winds will develop in the lee of the Absarokas and from Rock Springs through Casper today. Mixing and smoke dispersal will be generally poor. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Sunday evening through late Sunday night for WYZ015-018>020-022-030. Winter Storm Watch from late tonight through Sunday evening for WYZ001-002-012-013-023-024. Winter Storm Watch from Sunday afternoon through Sunday evening for WYZ010-011. High Wind Watch from 6 PM MST this evening through Sunday morning for WYZ003. Winter Storm Watch from Sunday morning through Sunday evening for WYZ014-025. Winter Storm Watch from Sunday morning through Sunday evening for WYZ008-009. && SHORT TERM...Hattings LONG TERM...Murrell AVIATION...LaVoie FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 142 AM MST Sat Dec 29 2018 WYZ001>020-022>030-301300- 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- 142 AM MST Sat Dec 29 2018 ...Winter Storm Watches in Effect late Saturday night into Sunday Night Across Portions of West and Central Wyoming... ...High Wind Watch in effect for the Cody Foothills tonight... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Significant snow expected to develop in Western Wyoming tonight. Strong to high wind is possible in the Cody Foothills tonight into Sunday morning. Windy from Rock Springs to Casper. .DAYS TWO THROUGH SEVEN...Sunday through Friday. Sunday and Sunday night...Snow and gusty north wind developing across the area with some significant accumulation. Tuesday...Potentially the coldest air of the season moving into the area. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight. TEAM RIVERTON
Special Weather Statement National Weather Service Riverton WY 605 AM MST Sat Dec 29 2018 WYZ026-292200- Upper Green River Basin- Including the cities of La Barge, Big Piney, and Farson 605 AM MST Sat Dec 29 2018 ...Snow and Strong Wind on Sunday... A cold front will move across the Upper Green River Basin on Sunday bringing light snow and strong northwest wind. * WHAT...Snow and Blowing Snow. Snow totals of 1 to 2 inches around and north of Daniel with an inch or less south of Daniel. Northwest wind 20 to 30 mph Sunday afternoon causing blowing snow. * WHERE...The Upper Green River Basin. * WHEN...Sunday. * ADDITIONAL DETAILS...Snowfall and blowing snow will reduce visibility and create slick, snow covered, or icy roads on Sunday. WYZ019-020-292200- Green Mountains and Rattlesnake Range- Natrona County Lower Elevations- Including the cities of Jeffrey City and Casper 605 AM MST Sat Dec 29 2018 ...Strong Southwest Wind this Afternoon through Sunday Morning... Southwest winds will intensify ahead of an approaching cold front. * WHAT...Southwest wind 25 to 35 mph with gusts over 50 mph. Stronger gusts are possible along Wyoming Boulevard on the south side of Casper. * WHERE...The lower elevations of Natrona County including the Casper area and along Highways 287 and 220 from Beaver Rim to the Rattlesnake Range. * WHEN...Saturday afternoon through Sunday morning. The strongest gusts are expected along Wyoming Boulevard on the south side of Casper on Sunday morning. * ADDITIONAL DETAILS...Strong wind gusts will pose a blow-over risk to lightweight high-profile vehicles. WYZ028-029-292200- Rock Springs and Green River-Flaming Gorge- Including the cities of Rock Springs and Green River 605 AM MST Sat Dec 29 2018 ...Snow and Strong Wind on Sunday and Sunday Night... A cold front will move across Sweetwater County on Sunday bringing light snow and strong west wind. * WHAT...Snow, strong wind, and areas of blowing snow. Snow totals on Sunday will be light with around an inch or less. West wind at 20 to 30 mph with gusts near 40 mph. * WHERE...Western Sweetwater County. * WHEN...Sunday and Sunday Night. * ADDITIONAL DETAILS...Snowfall and blowing snow will reduce visibility and create slick, snow covered, or icy roads on Sunday and Sunday night. Strong wind gusts may pose a blowover risk to lightweight high-profile vehicles. WYZ003-007-292200- Cody Foothills-Owl Creek and Bridger Mountains- Including the cities of Cody and Meeteetse 605 AM MST Sat Dec 29 2018 ...Strong West Wind this Afternoon through Sunday Morning... West winds will intensify ahead of an approaching cold front. * WHAT...West wind wind 25 to 35 mph with gusts over 50 mph. Stronger gusts are possible around Clark and along Highway 120 south of Cody. * WHERE...The Cody Foothills and Owl Creek Mountains. * WHEN...Saturday afternoon through Sunday morning. The strongest gusts are expected between 8 pm Saturday and 8 am Sunday. * ADDITIONAL DETAILS...Strong wind gusts will pose a blow-over risk to lightweight high-profile vehicles. WYZ017-292200- Wind River Basin- Including the cities of Riverton and Shoshoni 605 AM MST Sat Dec 29 2018 ...Snow and Blowing Snow Sunday Afternoon and Sunday Night... A cold front will move across the Wind River Basin on Sunday afternoon bringing snow and blustery north wind. * WHAT...Snow and Blowing Snow. Snow totals of 1 to 3 inches. North wind 15 to 25 mph and gusty. * WHERE...The Wind River Basin. * WHEN...Sunday afternoon and Sunday night. * ADDITIONAL DETAILS...Snowfall and blowing snow will reduce visibility and create slick, snow covered, or icy roads on Sunday afternoon and night. WYZ004>006-292200- North Big Horn Basin-Southwest Big Horn Basin- Southeast Big Horn Basin- Including the cities of Powell, Lovell, Greybull, Shell, Thermopolis, and Worland 605 AM MST Sat Dec 29 2018 ...Snow and Blowing Snow Sunday Afternoon and Sunday Night... A cold front will move across the Big Horn Basin on Sunday afternoon bringing snow and blustery north wind. * WHAT...Snow and Blowing Snow. Snow totals of 1 to 3 inches. North wind 20 to 30 mph and gusty. * WHERE...The Big Horn Basin. * WHEN...Sunday afternoon and Sunday night. * ADDITIONAL DETAILS...Snowfall and blowing snow will reduce visibility and create slick, snow covered, or icy roads on Sunday afternoon and night. TEAM RIVERTON/21
Special Weather Statement National Weather Service Riverton WY 607 AM MST Sat Dec 29 2018 WYZ003-291415- Cody Foothills- Including the cities of Cody and Meeteetse 607 AM MST Sat Dec 29 2018 A high wind watch is in effect for the Cody Foothills tonight and Sunday morning. Please see the high wind watch for more details.
The national radar mosaic for the moment the first event began.
5 winter storm, 1 high wind. Local standard time, as filed.
A maximum wind gust of 81 mph occurred to the south of Clark. At the Cody airport, there was a maximum wind gust of 58 mph.
Heavy snow fell in portions of the Tetons. The highest snowfall amount was 20 inches at the Grand Targhee SNOTEL site.
Heavy snow fell around Alpine where 10 inches of new snow fell. Amounts further south generally ranged from 3 to 6 inches.
A combination of periods of heavy snow and wind gusts over 50 mph brought near whiteout conditions that caused the closure of Interstates 25 and 90 for several hours. Snowfall amounts generally ranged from 3 to 6 inches.
Heavy snow fell around Thermopolis where up to a foot of new snow fell. Amounts lessened further north as the upslope component from the Owl Creek Mountains lessened.
The combination of heavy snow and strong winds caused the closure of Route 789 through Wind River Canyon.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2018Every state in 2018This day in weather historyWarnings in Wyoming, December 2018
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: 798146, 798147, 798148, 798150, 798153, 798154.