The first widespread winter storm of the season hit western and central Wyoming. The main effects from the storm were focused around central Wyoming.
Every event with a place to put it; 10 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.
The first widespread winter storm of the season hit western and central Wyoming. The main effects from the storm were focused around central Wyoming. Areas favored by east to northeast flow received the most snow, especially in Johnson and Natrona counties. Areas near Buffalo received the most snow with up to 18 inches reported on the west side of town. In Natrona County, areas around Casper received anywhere from 10 to 18 inches, although amounts dropped substantially farther west. Amounts over 6 inches were also reported in Fremont and Hot Springs counties. In the higher elevations, the eastern slopes of the Bighorn Range had the most with up to 20 inches reported. The snow combined with a gusty wind to close many major roads for a time, including Interstate 25, US 20/26, and US 287.
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 Oct 11, 3:01 AM MST, 59 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 401 AM MDT Mon Oct 11 2021 .SHORT TERM...Today through Tuesday night Showers have begun to increase across the north and west as a deepening trough approaches the state. The associated cold front is currently along the MT/WY border and will move south through the day. Mountain snow and lower elevation rain will continue, increasing in coverage this afternoon. Precipitation will transition to all snow tonight as reinforcing cold air drops the snow level to the basin floors. As the low deepens over the Great Basin and shifts over the CO Rockies on Tuesday, favorable northeasterly upslope flow will set up across areas east of the Divide. The heaviest snow will generally fall before noon across most areas, although heavier rates will continue across eastern areas into Tuesday night. Snow should begin tapering off by sunrise Wednesday, ending across eastern areas by early afternoon. Overall, the highest snow totals will generally be east of the Divide - especially along favorable upslope locations - with only 1 to 3 inches in the western valleys. One thing to note will be the relatively warm temperatures in the low to mid 30s across the lower elevations Tuesday afternoon, possibly hampering accumulations somewhat on warmer surfaces. Also to note will be strong north winds on Monday night and Tuesday with the tight pressure gradient; sustained wind over 30 mph with gusts over 40 mph are possible, especially in the Wind Corridor. .LONG TERM...Wednesday through Sunday With the focus on the near-term, very few changes were made to consensus guidance in the extended. Snow will be ending across Johnson and Natrona counties Wednesday morning, with breezy west to northwest winds continuing across much of the area Wednesday afternoon, in the wake of the storm. An upper level trough will move over the region early Thursday morning and exit the area by Friday morning. Isolated to scattered snow showers will redevelop over western and southern portions continue, with the main light accumulations focused over the mountains. Temperatures slowly warm into the weekend, but remain 10 to 15 degrees below average Saturday and Sunday. Dry conditions will be in place from Friday afternoon through Sunday, with mostly zonal flow and low- amplitude ridging aloft. && .AVIATION...For the 06Z TAFS through 06Z Tuesday Issued at 1126 PM MDT Sun Oct 10 2021 East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals A strong cold front will push quickly southward across northern Wyoming between 06Z and 12Z reaching the Bridger/Owl Creek Mountains, and the Johnson/Natrona County line around 12Z. In the wake of this cold front, ceilings will quickly lower from MVFR to IFR across the Cody Foothills between 08Z and 12Z. Steady precipitation is also expected at KCOD by around 09Z with rain changing to all snow by 12Z. Across the rest of the Bighorn Basin ceilings look to lower to MVFR/possibly IFR between 15Z and 18Z. The precipitation will also be more showery in nature and generally be rain. By 18Z, the cold front will have pushed across the rest of the area, but ceilings across the Wind River Basin and Natrona County are expected to remain roughly between 040-080 kft agl with some rain showers developing in the afternoon. Between 00Z and 03Z Tuesday, KCPR, KLND and KRIW will likely have ceilings lower to MVFR. Steady precipitation is expected to break out in those areas between 02Z and 05Z Tuesday. Precipitation looks to begin as a rain or a mixture or rain and snow, before changing to all snow between 02Z and 06Z at KLND, KRIW, and KWRL. KCPR might not completely change over to snow until between 06Z and 09Z Tuesday. IFR conditions are likely to develop at all terminals tonight, but at various times, and then likely remain IFR for the rest of the night. One note, KCOD will likely remain generally IFR after 12Z this morning with the possibility rising to MVFR for a few hours in the afternoon into early evening before lowering back to IFR. Northern mountains will become obscured between 08Z and 12Z, and remain so through the rest of the period, while the central mountains will begin to become obscured toward 00Z Tuesday, and then remain that way through the TAF period. In wake of the cold, breezy to windy northerly winds will occur, but more easterly in the Wind River Basin during the day. By 00Z Tuesday, the Wind River Basin will also switch to the northeast. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Isolated to scattered valley rain/mountain snow showers will generally occur along and north of a KAFO-KPNA line through 00Z Tuesday. The best chance will be areas from KJAC northward. The current thinking is the steady precipitation will remain north into Yellowstone during the day. Between 00Z and 03Z Tuesday, steady precipitation is expected to breakout at the KJAC terminal with a rain or rain/snow mixture changing to all snow by around 03Z. South into the Upper Green River Basin, and Sweetwater County, the precipitation will likely remain showery in nature with the change over to snow might not occur until around 06Z Tuesday. Breezy south to southeast winds will occur across the southwest and south Monday afternoon into the evening. The strong cold front will then push southwest across Sweetwater County between 02Z and 06Z Tuesday with strong east northeast winds at the KRKS terminal. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... A cold front is progressing southward through areas east of the Divide this morning. The front will reach the Divide by midday and cross the Divide this evening, passing through southern zones tonight. Rain and snow showers will be confined to northern portions this morning, gradually spreading over far western portions this afternoon. Showers will be widespread across areas east of the Divide tonight, with rain changing to snow this evening. Snow showers will be more scattered across the south tonight. Snow will continue across the area Tuesday, gradually ending from west to east Tuesday night into Wednesday morning. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 1 AM Tuesday to 6 AM MDT Wednesday for WYZ029-030. Winter Storm Warning from 6 PM this evening to noon MDT Wednesday for WYZ010-011-019-020. Winter Storm Warning from 6 PM this evening to 11 PM MDT Tuesday for WYZ016>018. Winter Weather Advisory from 6 PM this evening to 11 PM MDT Tuesday for WYZ012-024. Winter Storm Warning until 11 PM MDT Tuesday for WYZ002-003-005- 007-014-015. Winter Storm Warning until noon MDT Tuesday for WYZ001. Winter Storm Warning from 1 AM Tuesday to noon MDT Wednesday for WYZ022. Winter Storm Warning until noon MDT Wednesday for WYZ008-009. Winter Storm Watch from this evening through Tuesday evening for WYZ004-006. && SHORT TERM...Myers LONG TERM...VandenBoogart/LaVoie AVIATION...Murrell FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 345 AM MDT Mon Oct 11 2021 WYZ001>020-022>030-120945- 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- 345 AM MDT Mon Oct 11 2021 ...Multiple Winter Storm highlights in effect for much of western and central Wyoming through Wednesday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. A winter storm will begin to impact northern portions of the forecast area this morning, as a cold front progresses east of the Divide. Rain and snow showers will develop over far western portions this afternoon. Rain will change to snow this evening, as precipitation becomes widespread through the overnight hours. North to northeast winds, with gusts of 25 to 40 mph, will also occur tonight. Please see the winter weather products for more details, such as timing and potential snow amounts. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday through Wednesday...Snow will continue across the area through the day Tuesday, ending from west to east through the overnight hours. Snow will end over Johnson and Natrona counties Wednesday morning. High snowfall amounts are likely in the mountains and for low elevation areas east of the Continental Divide. Winter weather products detail the timing and amounts expected, so please see those for more detailed information. Temperatures will also be well below average with breezy to strong winds throughout the event. Thursday through Thursday night...Light snow showers expected in the western mountains. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
The national radar mosaic for the moment the first event began.
9 winter storm, 1 avalanche. Local standard time, as filed.
Heavy snow fell throughout the eastern Bighorn Range. The highest amount was 20 inches at the Soldier Park SNOTEL site.
Heavy snow fell in portions of the western Bighorn Range. The highest amount of snow reported was 15 inches at the Bald Mountain SNOTEL site at the north end of the range.
Heavy snow fell throughout northern Johnson County, with most locations receiving between 12 and 18 inches. The heavy snow led to the closure of Interstate 25 for several hours.
Heavy snow fell over portions of southern Johnson County, with the maximum accumulation of 14 inches to the east of Kaycee. The heavy snow led to the closure of Interstate 25 for many hours.
Heavy snow fell in portions of Hot Springs County. A trained spotter reported 6.5 inches to the northeast of Thermopolis.
A trained spotter reported 8 inches of snow in Hudson. Amounts dropped sharply farther north with Riverton reporting anywhere from 2 to 4 inches of snow.
Amounts around the Lander and the adjacent foothill communities ranged from 6 to 9 inches, including 7.9 inches at the Lander Airport.
A combination of snow and gusty wind led to the closure of US 287 for several hours.
Snowfall amounts around Casper ranged 12 to 18 inches, including 12.7 inches at the Casper-Natrona County International Airport. The heavy snow led to the closure of Interstate 25 as well as US 20/26 west of Casper. Snowfall amounts tapered off to the west with 6 inches reported at Powder River.
A combination of snow and gusty wind led to the closure of Wyoming Highway 28 over South Pass for several hours on Tuesday, October 12.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2021Every state in 2021This day in weather historyWarnings in Wyoming, October 2021
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: 987369, 987368, 987370, 987371, 987367, 987372, 987373, 987374, 987375, 987366.