A cold front swept across western and central Wyoming from Friday into Saturday and brought heavy snow and difficult travel conditions to many areas. The heaviest snow fell in Absarokas where 21 inches fell in Pahaska.
Every event with a place to put it; 9 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 western and central Wyoming from Friday into Saturday and brought heavy snow and difficult travel conditions to many areas. The heaviest snow fell in Absarokas where 21 inches fell in Pahaska. A foot or more of new snow also fell in portions of Yellowstone Park and the Tetons. The heaviest snow in the lower elevations fell in northern Wyoming. Some notable amounts include 10 inches at Bondurant, 9 inches in Cody and 10 inches in Thermopolis. Even in areas that received less snow, the combination of snow, gusty wind and black ice from rapidly falling temperatures brought very difficult travel conditions. Interstates 25 and 80 were shut down for a time, as well South Pass over the Wind River Mountains.
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 Nov 23, 11:08 AM MST, 3 hours 52 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Riverton WY 1108 AM MST Fri Nov 23 2018 .SHORT TERM...Today through Sunday night Overview...The forecast area remains poised for active weather today and Saturday, as a significant storm system/low pressure center, originating over AK/the North Pacific, moves onshore over the PACNW this afternoon. This storm will bring a cold front and enough Pacific moisture for moderate snow across the far west. This system will move across E ID/SW WY/NW CO tonight into Saturday, before exiting over the Central Plains Saturday night. Heavy amounts of snow will be possible for the far west, along with strong northwest winds behind the cold front across southern portions late tonight into Saturday morning. Synopsis...A lead shortwave, that is currently moving over ID, will bring a quick burst of snow early this morning to the far west. Snowfall amounts of 1 to 2 inches in the valleys and 2 to 3 inches in the mountains will occur by sunrise today. Light snow will continue to linger, with mainly flurries between 10am and 2pm. Snow will then increase through the rest of the afternoon, as another shortwave ahead of the main storm system brings a swath of Pacific moisture to the region. Moderate, with periods of heavy snow, will then occur across the far west after 00Z Saturday. This will continue through the overnight hours, before winds turn NW behind the cold front. This front will enter northwest portions after 06Z Saturday and quickly pass through the rest of the forecast area by 15Z. 700mb WNW winds will occur behind the front, which will not be as conducive for favorable orographics. This, coupled with downsloping winds and drier air, will keep additional snow amounts relatively light Saturday afternoon. The main impact with the aforementioned 700mb winds will be speeds of 40 to 50kt ahead and behind the cold front. High winds will occur in wind prone locations, like the Wind Corridor, this afternoon. These winds will subside briefly this evening, before increasing again late tonight. The strong winds tonight will mainly occur across southern portions and continue through Saturday morning, as the cold front blasts through the area. The I-80 corridor will be significantly impacted, as most of the snow will fall as the cold front moves across the area. This, coupled with the strong winds, will create blizzard-like conditions. Depending on how much snow falls during the 06Z - 15Z period, there could be ground blizzard conditions that continue Saturday afternoon. Impacts for areas east of the Divide, will be relatively minor in comparison. In addition to the high winds to impact areas from Jeffrey City to Natrona County this afternoon, gusty N to NW winds of 30 to 40 mph will occur over the Bighorn and Wind River basins and the I-25 corridor Saturday afternoon. Snow will be light for most areas east of the Divide, although there could be a quick burst of 1 to 2 inches Saturday afternoon from Jeffrey City and much of Natrona County. This could lead to near-whiteout conditions in these areas. Forecast snowfall amounts remain on track, with 4 to 8 inches in the western valleys, 12 to 24 inches in the western mountains; 2 to 3 inches across the I-80 corridor; 1 to 2 inches east of the Divide. Snow will quickly end across the area Saturday night, as the storm system exits over the Central Plains. Conditions will be dry and cold Sunday. .LONG TERM...Monday through Friday Overview...Dry and cool conditions will prevail across the area on Monday. A series of Pacific storm systems will bring chances of snow mainly along and west of the Continental Divide Tuesday through Friday. Temperatures will be close to seasonal normals Tuesday through Friday. Discussion...The large-scale pattern to begin this period on Monday features high amplitude ridge over the Intermountain West with broad trough downstream across the central and eastern U.S., and zonal flow across the Pacific with 160 knot jet translating the eastern Pacific along 40N. A dry northwest flow will prevail over west and central Wyoming on Monday. Strong Pacific jet streak will nose into California on Tuesday and undercut/breakdown ridge over the Intermountain West by Wednesday. ECMWF has shown better run-to-run consistency with evolution of southern storm track mid to late week than GFS. ECMWF shows sub-tropical jet translating the southern/central Rockies midweek while GFS shows less separation between northern and southern streams. Forecast is weighted toward ECMWF, and thus brings chances of precipitation into the west on the fast side on Tuesday. PoPs are then trended lower Thursday and Friday as flow becomes increasingly split with storm track and heavier precipitation headed south of Wyoming. Medium-range models show a very active storm track continuing across the Pacific and western U.S. into the first few days of December. It's beginning to look a lot like...El Nino. && .AVIATION...For the 18Z TAFS through 18Z Saturday East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes The main concern through 00Z Saturday will be windy west to southwest wind and low-level wind shear on the lee side of mountain ranges into the adjacent foothills. Very windy southwest wind will occur from South Pass to Casper. Otherwise, VFR conditions will occur. Late tonight, there could be some shower activity that spreads northeast possibly impacting southeast Fremont into Natrona counties, as well as the northern Bighorn Basin and Bighorn Mts. The best shot at snow will be in wake of a cold front, which should be pushing into N Wyoming around 15Z Saturday. West of the Divide...KBPI/KJAC/KPNA/KRKS Routes A break in the snow is expected for much of the area through 22Z, when terminals are expected to be VFR. After 22Z, but especially after 01Z Saturday, conditions will once again deteriorate as another storm system begins to spread snow back to the area. IFR conditions are likely to develop over the far west, including KJAC in the late afternoon or early evening spreading east and southeast during the evening possibly impacting KRKS by around 05Z Saturday. Blowing snow will also become an issue as the night wears on. The snow could begin to taper off across parts of the west toward 14Z Saturday, but blowing snow will probably persist or get worse. Toward the tail end of the most active weather, a heavy band of snow will move off the western mountains and valleys and stream across Sweetwater County, including KRKS, where this brief period of heavy snow and blowing snow, along with high winds, will arrive around 15Z Saturday. In addition, there will be low-level wind shear at times at area terminals through the period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued AT 1253 AM MST Fri Nov 23 2018 A major winter storm will impact the area today and Saturday, with significant snow amounts across the west. High to possibly strong winds will occur across the Wind Corridor this afternoon, with strong winds developing late tonight across the south and southwest. These winds will continue through Saturday morning, with gusty north- northwest winds for areas east of the Divide Saturday afternoon. Temperatures will remain seasonal Friday before cooling for the weekend. Despite low mixing heights, smoke dispersal will be good Friday and Saturday because of the very windy conditions. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 5 PM this afternoon to 11 AM MST Saturday for WYZ028>030. Winter Weather Advisory from 6 PM this evening to midnight MST Saturday night for WYZ019. Winter Weather Advisory from 6 PM this evening to 11 AM MST Saturday for WYZ026. Winter Storm Warning from 11 AM this morning to 11 AM MST Saturday for WYZ001-002-012>015-023>025-027. && SHORT TERM...LaVoie LONG TERM...Meunier AVIATION...Murrell/Lipson FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 209 PM MST Fri Nov 23 2018 WYZ001>020-022>030-241200- 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- 209 PM MST Fri Nov 23 2018 ...Winter Storm Warnings in effect for today and Saturday across the Western Mountains and Valleys and Sweetwater County... ...Winter Weather Advisories in effect tonight and Saturday for portions of Sublette County and the Rattlesnake Range/Green Mountains... ...Winter Weather Advisory Johnson County Saturday... ...Winter Weather Advisory Natrona County 11 AM Saturday through 8 PM Saturday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight Snow, heavy at times, along with strong west wind will result in hazardous winter conditions across the western mountains and valleys this afternoon. The snow will increase across southwest Wyoming tonight. Strong wind, combined with a quick shot of snow, could produce hazardous travel conditions along Interstate 80 tonight. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Saturday...Hazardous travel conditions will continue during the day along the Interstate 80 corridor, as light snow with high to strong northwest winds continue. will create hazardous travel conditions across central and northern Wyoming. Snow, along with a gusty to strong north wind, will create hazardous travel conditions across central and northern Wyoming. Tuesday through Thursday...Chances of mainly light snow in the western mountains and far west valleys. .SPOTTER INFORMATION STATEMENT... Spotters are urged to report snowfall amounts and wind gusts. Thank you. Team Riverton
The national radar mosaic for the moment the first event began.
9 winter storm. Local standard time, as filed.
Heavy snow fell in portions of Yellowstone Park. The SNOTEL sites at Lewis Lake Divide, Parker Peak and Two Ocean Plateau recorded 12 inches of new snow.
Heavy snow fell in portions of the Tetons. The highest amount recorded was 13 inches at the Grand Targhee SNOTEL site.
Heavy snow fell across much of the Jackson Valley. Snowfall amounts generally ranged from 6 to 10 inches.
Heavy snow fell in portions of the Green River Foothills. Some of the highest snowfall amounts included 10.5 inches at Bondurant and 6 inches at Pinedale.
Heavy snow fell in the Absarokas. The highest report was 21 inches at Pahaska. Other notable amounts included 17 inches at the Marquette SNOTEL and 12 inches at the Wapati SNOTEL site.
A combination of snow and strong wind closed South Pass for several hours.
Heavy snow fell in portions of the Cody Foothills. The highest amount recorded was 13 inches at Wapati. The city of Cody had amounts ranging from 6 to 11 inches.
A combination of snow, wind and black ice led to closure of Interstate 80 from Rock Springs to the Carbon County line for several hours.
Heavy snow fell throughout much of Hot Springs County. Amounts of 6 to 10 inches were measured through Thermopolis to 12 inches 8 miles WNW of Thermopolis.
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, November 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: 788469, 788471, 788472, 788474, 788470, 788473, 788476, 788475, 788477.