Heavy, wet snow fell across portions of central Wyoming. The greatest snowfall occurred in the higher elevations of the Wind River Range, with a peak total of 20 inches estimated at the Hobbs Park SNOTEL site.
Every event with a place to put it; 3 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.
Heavy, wet snow fell across portions of central Wyoming. The greatest snowfall occurred in the higher elevations of the Wind River Range, with a peak total of 20 inches estimated at the Hobbs Park SNOTEL site. Heavy snow also fell in Natrona County, where up to 14 inches fell on Casper Mountain and 10 inches in the city of Casper.
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 18, 10:59 PM MST, 1 hour 1 minute earlier.
Area Forecast Discussion National Weather Service Riverton WY 1159 PM MDT Mon Oct 18 2021 .UPDATE... Issued at 1002 PM MDT Mon Oct 18 2021 Updated to include the Lander Foothills into an advisory from 6 AM to 3 PM Tuesday. Looks like snowfall rates and a change over around sunrise could make roads slick and slushy across the Lander Foothills. && .SHORT TERM...This Afternoon through Tuesday night Warm and dry conditions continue across the forecast area this afternoon, as mid to high level clouds increase from the south- southwest. Rain showers and high elevation snow will be possible over far western portions by sunset this evening, as the cutoff low (currently over northeast NV) continues its eastward approach to the region. Precipitation chances increase across much of the forecast area through the evening as the low moves along the WY/CO border, becoming likely across central and southern portions by midnight. The best chances for snow tonight will be across southern portions, especially the Upper Green River Basin near Big Piney, Daniel and the Wyoming Range. In addition, heavy snow along the east slopes of the Wind River Mountains is now likely tonight after midnight as snow levels lower to around 7000 ft across the area. Temperature variability at the surface continues to be a challenge tonight and Tuesday morning. Moderate to heavy precipitation will develop after midnight through Tuesday morning over areas east of the Divide, from southern portions of the Bighorn Basin, southern Johnson County to the Wind River Basin and Natrona County. Do not expect most places in the Wind River Basin and Natrona County to have snow during this time, as dewpoints should be rising through the overnight hours due to the southerly flow. Although there is a chance for the wet bulb temperature to drop to freezing due to heavier precipitation, this is not likely for most of these areas during this timeframe. However, this could occur at Lander toward sunrise and the rest of Tuesday morning. This will have to be closely monitored. Precipitation will begin to end west of the Divide through the morning hours Tuesday, with the focus being east of the Divide through the day. Rain will change over to snow over western portions of Natrona County Tuesday morning, with the change over occurring in the Casper area sometime around midday. Moderate to heavy snow remains possible due to the wet snow and high snowfall rates. The rest of Natrona County will have these impacts as well. Have opted to leave southern Johnson County out of the Winter Storm Warning, as locations like Linch and Sussex would likely be the only ones impacted. Snow chances become less likely for the Wind River and Bighorn Basins by Tuesday afternoon, due to lower precipitation chances. This would affect snowfall rates and temperatures. If snow is able to fall, it would likely only accumulate in grassy areas. Precipitation will quickly end from west to east Tuesday evening, ending shortly after midnight, as the storm exits over the Plains. Clouds will be slow to clear out, so fog formation is not expected at this time. However, if clouds due clear out quickly enough, fog will be possible Wednesday morning for much of the aforementioned areas. .LONG TERM...Wednesday through Monday Shortwave ridge transits the forecast area Wednesday in the wake of the departing winter storm. Temperatures rebound slightly, but remain below normal. This trend continues Thursday, as mid-level temperatures slowly warm. However, the warm-up is tempered both Wednesday and Thursday across Natrona County and nearby locations, due to new snow cover. The tail end of a weak system moving through the northern Intermountain West may clip the northwest late Wednesday night and Thursday morning. Other than a few flurries, there will be nothing more than increased cloud cover during the period. Otherwise, dry conditions and a breezy Wind Corridor prevail Wednesday and Thursday. The next ridge sharpens to our west Thursday night in response to a developing long wave trough off the West Coast. This ridge traverses the state Friday. Dry conditions continue with an increase in mid and high level clouds late in the day. Temperatures climb back to near seasonal averages in the 50s, as 700 mb temperatures warm to +3C to +5C. Would not be surprised if we saw a few 60s across the east, depending upon timing of cloud cover. West to southwest flow aloft increases for the weekend into next week ahead of the long wave trough. Multiple pieces of shortwave energy eject from the trough and cross the region Saturday through Monday. Overall, we should see a gradual increase in precipitation chances during the three-day period. Initially, the precipitation will be mainly in the mountains west of the Continental Divide (Saturday), increasing in the mountains and valleys of the west (Sunday), and become more widespread in the central basins and southwest (Monday). Seasonal temperatures over the weekend will trend downward Monday given the increased cloud cover and precipitation. Also of note is the gradually increasing westerly surface wind. A favorable jet position could lead to a windy start to next week. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) Issued at 1150 PM MDT Mon Oct 18 2021 East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals Light rain will continue to become widespread across the Wind River Basin and Natrona County through 09Z...and then across the southern Bighorn Basin between 10Z and 14Z. The intensity of the precipitation will increase between 10Z and 15Z with a changeover to predominantly snow as well as IFR conditions developing at at KCPR, KLND, and KRIW terminals. KCOD and KWRL terminals will remain mainly rain with a possible mix of snow at KCOD Tuesday morning with MVFR ceilings. IFR and MVFR conditions will continue through much of the TAF period across the Wind River Basin, Natrona County, and Johnson County. The Bighorn Basin should improve to VFR between 21Z Tuesday and 00Z Wednesday. The precipitation will end from west to east late Tuesday afternoon and Tuesday evening. Some snow could linger across Johnson and Natrona counties through about 06Z Wednesday. Gusty northerly winds will occur in most locations through about 00Z Wednesday, except perhaps the Wind River Basin. Mountains will be obscured much of the time. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Widespread precipitation will generally occur south of a line from K46U (Alpine) to 20NW KPNA with much less precipitaion north of that line including KJAC. The precipitation could begin as rain, but should change quickly to snow in the Upper Green River Basin while KRKS might not change until around 12Z. IFR to MVFR conditions are expected in those areas through about 18Z with most locations improving to VFR by early Tuesday afternoon. Isolated showers could redevelop by around 21Z at KBPI, KPNA, and KJAC, before ending by 03Z Wednesday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Increasing chances for rain and snow across much of the area tonight. Heavy snow expected for zones 285, 286, 287, 288 and 300 tonight into Tuesday. Rain to a rain snow mix will occur east of the Divide Tuesday, with the best chances for snow across Natrona County. Snow will end west of the Divide Tuesday morning and east of the Divide Tuesday evening. Dry conditions will be in place Wednesday through Friday, with precipitation chances returning to far western Wyoming by Saturday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM to 11 PM MDT Tuesday for WYZ019. Winter Weather Advisory from 6 AM to 3 PM MDT Tuesday for WYZ018. Winter Storm Warning until 6 PM MDT Tuesday for WYZ015. Winter Weather Advisory until 6 PM MDT Tuesday for WYZ002-014. Winter Weather Advisory until noon MDT Tuesday for WYZ025-026. Winter Storm Warning from 3 AM to 11 PM MDT Tuesday for WYZ008- 009-020-022. Winter Weather Advisory from 3 AM to 6 PM MDT Tuesday for WYZ007. && UPDATE...Murrell SHORT TERM...LaVoie LONG TERM...CNJ AVIATION...Murrell FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 250 PM MDT Mon Oct 18 2021 WYZ001>020-022>030-192100- 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- 250 PM MDT Mon Oct 18 2021 ...Winter Weather headlines in effect from early Tuesday Morning through Tuesday Night... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon through Tonight. Scattered mountain snow and valley rain showers developing over far western portions by this evening. Precipitation will become widespread tonight, with rain changing over to snow after midnight. Areas of rain and snow will continue, especially east of the Divide. See winter weather headlines for more details. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday...Rain and snow likely east of the Divide. Snow becoming likely across western portions of Natrona County through the morning and the rest of the county by midday. See winter weather headlines for more details. Saturday and Sunday...Rain and snow is possible over western portions of the state. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
Special Weather Statement National Weather Service Riverton WY 951 PM MDT Mon Oct 18 2021 WYZ024-191230- Salt River and Wyoming Ranges- 951 PM MDT Mon Oct 18 2021 ...Accumulating Snowfall Tonight and Tuesday Morning... This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Snowfall amounts of 3 to 6 inches, with locally higher totals around 8 inches on east-facing slopes of the Wyoming Range. * WHERE...Salt River and Wyoming Ranges. * WHEN...Now through Tuesday Morning. WYZ016-017-191230- Upper Wind River Basin-Wind River Basin- Including the cities of Dubois, Riverton, and Shoshoni 951 PM MDT Mon Oct 18 2021 ...Rain and Snow Arrives Late Tonight and Tuesday Across the Wind River Basin... This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Rain or a rain and snow mix early Tuesday morning will change over to snow Tuesday morning. Snow totals of 2 to 4 inches is expected above 5200 feet. Below 5200 feet, a skiff to around 1 inch is expected to accumulate. * WHERE...Wind River Basin. * WHEN...Late tonight through Tuesday. WYZ011-191230- Southeast Johnson County- Including the city of Kaycee 951 PM MDT Mon Oct 18 2021 ...Snow Increases through the Day on Tuesday... This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Rain or a rain and snow mix early Tuesday morning will change to all snow after sunrise. Accumulations over far southern Johnson County will reach 2 to 4 inches. * WHERE...Southern Johnson County. * WHEN...Tuesday and Tuesday Evening. * ADDITIONAL DETAILS...Local snowfall of 4 to 6 inches possible near the Natrona County line mainly south of Kaycee and Sussex...as well as west of Interstate 25. Team Riverton/21
Special Weather Statement National Weather Service Riverton WY 953 PM MDT Mon Oct 18 2021 WYZ018-190500- Lander Foothills- Including the city of Lander 953 PM MDT Mon Oct 18 2021 The Lander Foothills is now in a winter weather advisory from 6 AM to 3 PM Tuesday. 21
The national radar mosaic for the moment the first event began.
3 winter storm. Local standard time, as filed.
Heavy snow fell in portions of the Wind River Range. The highest amount estimated was 20 inches at the Hobbs Park SNOTEL site.
Heavy snow fell on Casper Mountain, with the Reno Hill SNOTEL estimated to have received a maximum amount of 14 inches.
A trained spotter reported 10 inches of snow on the southwest side of Casper. Amounts dropped farther north and across the lower elevations, with 5 inches of snow reported at the Casper-Natrona County International Airport.
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: 988587, 988589, 988588.