Low pressure tracking northeastward across Wyoming produced heavy snow along the eastern slopes of the Bighorn range as low level flow turned upslope. The highest snowfall total reported was 16 inches at the Hansen Sawmill SNOTEL site.
Every event with a place to put it; 1 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.
Low pressure tracking northeastward across Wyoming produced heavy snow along the eastern slopes of the Bighorn range as low level flow turned upslope. The highest snowfall total reported was 16 inches at the Hansen Sawmill SNOTEL site.
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 Apr 21, 2:00 AM MST, 1 hour earlier.
Area Forecast Discussion National Weather Service Riverton WY 300 AM MDT Fri Apr 21 2017 .SHORT TERM...Friday through Sunday night Another day of mashing of teeth with the uncertainty in the forecast. Much like a couple of weeks ago, the key phrase of the day will be 1 or 2 degrees; or in a similar vain, 100 or 200 feet. This is all it will take in many areas to make the difference between just a cold front and a heavy, wet snow. The radar continues to fill in as low pressure moves across the area. What we do know is that it will be a cloudy, cool and wet day for many areas East of the Divide. However, since the precipitation looks to be banded in nature for many areas, pinpointing the exact locations of the heaviest QPF is difficult at best. As for the highlights, they look reasonable so we will continue them as is. This will be the same situation for the Special Weather Statements as well. 700 millibar temperatures will be in that critical minus 5 to minus 7 range as well. A lot may depend on precipitation rate with any possible dynamic cooling. Complicating matters even further today will be the high late April sun angle. This could be a situation in some areas where there is several inches of snow on the grass and very little on paved surfaces. To sum it up, we made very few changes to continuity as this may be a situation where we are reacting to heavier bands of snow that pop up, stay tuned. Meanwhile, out west the steadier precipitation will end, although with the atmosphere becoming unstable with daytime heating, snow showers will remain possible. As low pressure moves away tonight, there should be a lessening in intensity and coverage from west to east, although rain and snow should linger in the east much of the night. Transitory ridging building across the area should then bring a return to dry weather for all areas by noon Saturday along with a good deal of sunshine. High temperatures could be a bit tricky though, depending on any snow cover and heating going toward melting snow rather than heating the air. On Sunday, the next system will approach the west. However, the models have trended a bit further north with the best energy. For now, any showers during the day should be confined to areas West of the Divide. Meanwhile, areas East of the Divide should see a nice end to the weekend with mild temperatures and light to moderate wind with sunshine mixing with high clouds. Some showers may spread East of the Divide Sunday night although at this point it does not look like a big event. .LONG TERM...(Monday through Friday) Issued at 154 AM MDT Fri Apr 21 2017 The GFS and ECMWF models are painting an unsettled weather pattern for the last week of April. Differences in the pattern show up Wed night and continue through Friday with respect to the timing of weather systems in the westerly flow aloft. Areas along and west of the continental divide look to see periods of rain and snow Mon through Fri with mainly snow in the mountains above 7500 feet. The potential exists for significant snow accumulations above 8500 feet in the western mountains which could lead to travel issues over the passes. Will be keeping an eye on this pattern in the coming days to better time the heavier snowfall events. Meanwhile, east of the divide, the weather pattern looks to be showery at times on any given day or night. Some places may be totally dry on a given day while other locations could see some precipitation each day. Again, will adjust the forecast as needed based on model consistency. High temps will be on the cool side Mon through Fri with near to below normal readings. Expect breezy to windy conditions at times in the favored wind corridors. && .AVIATION...12Z Issuance WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES Areas with MVFR ceilings are expected this morning over far western Wyoming, otherwise isolated to scattered snow showers are expected with brief MVFR/IFR conditions throughout the day. Windy northwest or west wind will occur across the Upper Green River Basin and Sweetwater County today. Tonight, decreasing cloudiness is expected with some fog possible after midnight. EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES Widespread MVFR/IFR conditions will likely occur at most locations through the day. Snow levels are expected to lower to around 5000 feet over the Big Horn, and Wind River Basins by 15Z with snow levels higher farther east. The worst conditions are expected at KCOD and KRIW where persistent IFR conditions could occur due to reduced visibility in snow. Precipitation is expected to gradually improve this evening from west to east, but could see some precipitation linger across Johnson/Natrona Counties through much of the night. Mountains will be obscured much of the time with IFR or LIFR conditions expected. && .FIRE WEATHER... Low pressure moving through the area will bring rain and snow showers to most areas today with the exception of the far southwest. As a result, a wetting rain is likely for many areas. Snow levels may reach valley and basin floors at times although pinpointing the heaviest rain or snow is difficult. Mixing and smoke dispersal will be generally fair to poor but except in southern Sweetwater county where it will be fair to good. A gusty north wind will also blow at times. Mainly dry weather will return Saturday as high pressure builds across the state. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until midnight MDT tonight for WYZ002- 007-015. Winter Storm Warning until 6 AM MDT Saturday for WYZ008-009. Winter Weather Advisory until midnight MDT tonight for WYZ003. && SHORT TERM...Hattings LONG TERM...AR AVIATION...Murrell FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 300 AM MDT Fri Apr 21 2017 WYZ001>020-022>030-221200- 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- 300 AM MDT Fri Apr 21 2017 ...Winter Weather Advisories for the eastern Wind River Mountains, Absaroka Mountains and Cody Foothills through this evening... ...Winter Storm Warning for the Bighorn Mountains through tonight... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight... Significant mountain snow across the forecast area with the Bighorn Mountains in position for probable heavy snow. Light to moderate snowfall expected elsewhere...especially across the northern half of Wyoming above 5000 feet. Please see the latest Winter Weather Products for details. .DAYS TWO THROUGH SEVEN...Saturday through Thursday... Sunday and Sunday night...A chance of rain and snow in the west with isolated thunderstorms. Monday through Thursday...Periods of rain and snow in the west. A daily chance of rain and mountain snow east of the continental divide. .SPOTTER INFORMATION STATEMENT... Spotters are urged to report rainfall, and or, snowfall amounts. Thank you.
Special Weather Statement National Weather Service Riverton WY 1007 PM MDT Thu Apr 20 2017 WYZ001-012-014-024-211000- Yellowstone National Park-Teton and Gros Ventre Mountains- Wind River Mountains West-Salt River and Wyoming Ranges- Including the cities of Lake, Mammoth, and Old Faithful 1007 PM MDT Thu Apr 20 2017 Scattered to numerous snow showers ongoing across the western mountains and Yellowstone National Park will gradually decrease in coverage and intensity after midnight. Additional snowfall amounts of 1 to 4 inches can be expected. WYZ016-211000- Upper Wind River Basin- Including the city of Dubois 1007 PM MDT Thu Apr 20 2017 Areas of rain and snow between Crowheart to Dubois will change to all snow during the predawn hours Friday. Scattered snow showers are then expected to continue during the day Friday. The heaviest precipitation is expected through about sunrise. 1 to 3 inches of snowfall could occur especially on elevated or grassy areas. WYZ017-018-211000- Wind River Basin-Lander Foothills- Including the cities of Riverton, Shoshoni, and Lander 1007 PM MDT Thu Apr 20 2017 Areas of rain will gradually become widespread across the Wind River Basin after midnight. The rain is then expected to change to snow in most locations between 6 AM and 9 AM especially above 5000 feet. Scattered to numerous mainly snow showers are expected to continue through the day Friday. 1 to 3 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur where snow bands persist, but pinpointing these locations are difficult at this time. Roads could become slick and hazardous during heavier bursts of heavy snow, but roads are currently expected to be mainly wet. WYZ019-211000- Green Mountains and Rattlesnake Range- Including the city of Jeffrey City 1007 PM MDT Thu Apr 20 2017 Areas of rain will gradually become widespread across the higher elevations of southeast Fremont County after midnight. The rain is then expected to change to snow during the predawn hours. Scattered to numerous snow showers are expected to continue through the day Friday. 1 to 4 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur where snow bands persist, but pinpointing these locations are difficult at this time. Highways especially over Beaver Rim will likely become slick and hazardous during heavier bursts of heavy snow. WYZ005-211000- Southwest Big Horn Basin- Including the city of Thermopolis 1007 PM MDT Thu Apr 20 2017 Areas of rain will gradually become widespread across Hot Springs County after midnight. The rain is then expected to change to snow in most locations between 6 AM and 9 AM. Periods of snow are expected to continue through the day Friday. 2 to 3 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur in the Hamilton Dome and south of Thermopolis near the mouth of the Wind River Canyon. Roads especially highway 120 northwest of Thermopolis will probably become slick and hazardous at times, while highway 20, 789 north of Thermopolis will likely just be wet. WYZ022-211000- Casper Mountain- 1007 PM MDT Thu Apr 20 2017 Scattered rain and snow showers tonight, will become all snow Friday morning. Scattered snow showers will then continue through the day Friday, and come to an end Friday evening. 2 to 5 inches with isolated higher amounts are expected over Casper and Muddy mountains. Roads over Casper Mountain could become slick and hazardous at times. 21
Special Weather Statement National Weather Service Riverton WY 157 AM MDT Fri Apr 21 2017 WYZ001-012-014-024-212130- Yellowstone National Park-Teton and Gros Ventre Mountains- Wind River Mountains West-Salt River and Wyoming Ranges- Including the cities of Lake, Mammoth, and Old Faithful 157 AM MDT Fri Apr 21 2017 Scattered snow showers will continue today. Additional snowfall amounts of an inch or two are expected although locally higher amounts are possible where snowbands develop. WYZ016-212130- Upper Wind River Basin- Including the city of Dubois 157 AM MDT Fri Apr 21 2017 Scattered snow showers are expected today Friday. The heaviest precipitation is expected through about sunrise. 1 to 3 inches of snowfall could occur especially on elevated or grassy areas. WYZ017-018-212130- Wind River Basin-Lander Foothills- Including the cities of Riverton, Shoshoni, and Lander 157 AM MDT Fri Apr 21 2017 Areas of rain will develop this morning. The rain is then expected to change to snow in most locations between 6 AM and 9 AM mainly above 5000 feet. Scattered to numerous mainly snow showers are expected to continue today. 1 to 3 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur where snow bands persist, but pinpointing these locations are difficult at this time. Roads could become slick and hazardous during heavier bursts of heavy snow, but roads are currently expected to be mainly wet. WYZ019-212130- Green Mountains and Rattlesnake Range- Including the city of Jeffrey City 157 AM MDT Fri Apr 21 2017 Areas of rain will gradually will develop this morning. The rain is then expected to change to snow during the morning hours. Scattered to numerous snow showers are expected to continue today. 1 to 4 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur where snow bands persist, but pinpointing these locations are difficult at this time. Highways especially over Beaver Rim will likely become slick and hazardous during heavier bursts of heavy snow. WYZ005-212130- Southwest Big Horn Basin- Including the city of Thermopolis 157 AM MDT Fri Apr 21 2017 Areas of rain will develop this morning. The rain is then expected to change to snow in many locations between 6 AM and 9 AM. Periods of snow are expected to continue today. 1 to 3 inches of snow could accumulate especially on grassy areas. Heavier amounts of snow could occur in the Hamilton Dome and south of Thermopolis near the mouth of the Wind River Canyon. Roads especially highway 120 northwest of Thermopolis will probably become slick and hazardous at times, while highway 20, 789 north of Thermopolis will likely just be wet. WYZ022-212130- Casper Mountain- 157 AM MDT Fri Apr 21 2017 Scattered rain and snow showers will develop and change to all snow this morning. Scattered snow showers will then continue through today, and come to an end Friday evening. 2 to 5 inches with isolated higher amounts are expected over Casper and Muddy mountains. Roads over Casper Mountain could become slick and hazardous at times.
The national radar mosaic for the moment the first event began.
1 winter storm. Local standard time, as filed.
Heavy snow fell along the eastern slopes of the Bighorn range. Some of the highest snowfall totals included 16 inches at the Hansen Sawmill SNOTEL and 15 inches at the Soldier Park SNOTEL.
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, April 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: 684349.