Low pressure moving up from the south brought locally heavy snow to the higher elevations of central Wyoming, largely above 8500 feet. This highest amount recorded was 17 inches at the Deer Park SNOTEL site in the Wind River Mountains.
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The episode as NWS RIW wrote it up.
Low pressure moving up from the south brought locally heavy snow to the higher elevations of central Wyoming, largely above 8500 feet. This highest amount recorded was 17 inches at the Deer Park SNOTEL site in the Wind River Mountains. In the Absarokas, 14 inches of new snow fell at the Marquette 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 30, 12:10 AM MST, 2 hours 50 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 110 AM MDT Mon Apr 30 2018 .SHORT TERM...Monday through Wednesday night As a former construction worker, I was unfortunate enough to touch an uninsulated wire one time. And this reminds me of the weather most areas will see today, a shock to the system. This time, not of the electric variety, but the weather variety. After a warm and windy today yesterday, we will turn the clock back about a month and a half. Colder air is moving in behind a cold front as I write this. At this same time, a good plume of moisture and some good upper level dynamics will be moving into the area. The result will be a triple C day in most areas, cloudy, cool and cruddy. This means rain at most of the lower elevations and snow in the mountains. The heaviest snow looks to last the longest across the Big Horns where forcing will last the longest and favorable flow could bring some heavy snow. In addition, with snow continuing at a good rate at night it has the best chance for decent accumulations on the roads over the passes. As a result, we upgraded the winter storm watches to warnings. Elsewhere, we went with advisories. In the Absarokas, there could be some local warning amounts, but these would be in areas with no roads and impacts would be minimal. In the Wind River Range, most snow would fall during the day today with the best lift shifting north at night. As a result, with the snow falling during the day and the very strong almost May sun angle, much of the snow would melt on roads. In addition, winds are not expected to be too strong so blowing snow should not be a big problem. Warning amounts are a decent possibility in the highest elevations but again, impacts will be minimal. We also went with an advisory for the Teton and Gros Ventre zone, but mainly for Togwotee Pass where upslope flow will be found and not as much of the Tetons. As for the lower elevations, the best chance for any accumulation would be around Cody. Expected 700 millibar temperatures around -4 would put snow levels around 6000 to 6500 feet, but a heavy rate could bring heavy, wet snow. However, accumulation on paved surfaces may be restricted due to the high sun angle and warm ground. We could also see it around Lander and Dubois although amounts would be limited. As for the chance of thunder, we can't rule out one or two but again, I'm not plastering the area for a couple of lightning strikes. Snow should gradually taper off late tonight as the forcing moves away to the north and east. Steady precipitation will end for Tuesday. However, with some instability hanging around, unsettled weather will continue into Tuesday. This would be primarily be across the north with drier weather to the south. Another system tracking to the south of the area will provide another chance of showers and a few thunderstorms for Wednesday although almost a reverse of Tuesday with the best chance across the south and diminishing chances further north. Small hail will be possible with any storm given the cool temperatures and low wet bulb zero levels. Temperatures will remain below normal on Tuesday and Wednesday but somewhat warmer than today. .LONG TERM...Thursday through Monday The persistent troughiness across the forecast area in the short-term will be finally exiting into the Plains with drier and warmer conditions expected Thursday. Weak ridging is expected Friday and Saturday with temperatures 5-10 degrees above average. Enough instability and moisture for isolated showers and perhaps a thunderstorm over the northern mountains and adjacent foothills Friday. A weak wave on Saturday, moving through the overall flat ridge ahead of an upper low/trough over the Pacific Northwest, will give a better shot of convection compared to Friday over and near the mountains. Medium range models then have a decent spread of solutions on the evolution of the upper low/trough early next week. However overall it looks like seasonal to slight above average temperatures and some chances of convection each day. && .AVIATION...12Z Issuance West of the Divide...KBPI/KJAC/KPNA/KRKS Routes Rain and snow with snow in the mountains will occur today into tonight. MVFR conditions will prevail with areas of IFR conditions through 06Z. Mountain obscuration will be common. The rain and snow will decrease in coverage after 06Z Tue with gradual improvement at the terminal sites. KJAC will be impacted after 18Z through 06Z Tue with precipitation and low ceilings. Please see individual terminal forecasts for more details. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes Rain with mountain snow will occur today into tonight. MVFR conditions will prevail at most terminal sites today into tonight with areas of IFR conditions. Rain may mix with snow or change to snow after 01Z Tue at some locations. Mountain obscuration will be common. Rain and snow gradually decreases after 06Z Tue with conditions slowly improving at the terminal sites. Please see individual terminal forecasts for more details. 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 dropping through the area will bring much cooler temperatures along with the a good chance of showers and snow in the higher elevations. There will be much less wind than yesterday with relative humidity remaining well above critical levels for most locations. Mixing and smoke dispersal will be fair to poor for most locations but good at times across southern Wyoming. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 6 AM this morning to 6 AM MDT Tuesday for WYZ002-008-009. Winter Weather Advisory from 6 AM this morning to 6 AM MDT Tuesday for WYZ014-015. Winter Weather Advisory from noon today to 6 AM MDT Tuesday for WYZ012. && SHORT TERM...Hattings LONG TERM...Murrell AVIATION...Ross FIRE WEATHER...Hattings
Hazardous Weather Outlook National Weather Service Riverton WY 112 AM MDT Mon Apr 30 2018 WYZ001>020-022>030-011200- 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- 112 AM MDT Mon Apr 30 2018 ...Winter Storm Warnings and Advisories in effect for the western and northern mountains through tonight... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Snow will develop across the mountains today and continue into tonight with moderate to heavy snow possible in spots. Please see winter weather products and forecasts for details. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday and Wednesday...Isolated afternoon and evening thunderstorms. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report snowfall amounts. Thank you.
Special Weather Statement National Weather Service Riverton WY 104 AM MDT Mon Apr 30 2018 WYZ026>030-302100- Upper Green River Basin-South Lincoln County- Rock Springs and Green River-Flaming Gorge-East Sweetwater County- Including the cities of La Barge, Big Piney, Farson, Kemmerer, Cokeville, Rock Springs, Green River, and Wamsutter 104 AM MDT Mon Apr 30 2018 A mixture of rain and snow will continue today. The precipitation will turn to mostly all snow this evening before ending . By this evening, snowfall accumulations across Southwest Wyoming will amount from a coating to 2 inches, with most of the snowfall occurring in the Upper Green River Basin Foothills. WYZ017>020-022-302100- Wind River Basin-Lander Foothills- Green Mountains and Rattlesnake Range- Natrona County Lower Elevations-Casper Mountain- Including the cities of Riverton, Shoshoni, Lander, Jeffrey City, and Casper 104 AM MDT Mon Apr 30 2018 Rain showers continue in the lower elevations today, with with snow at times with more snow in the higher elevations. By tonight, snowfall accumulations of an inch or less will occur along the Natrona Fremont County line as well as over Beaver Rim. Dubois and Casper Mountain could see up to 2 inches of snow. WYZ003-007-302100- Cody Foothills-Owl Creek and Bridger Mountains- Including the cities of Cody and Meeteetse 104 AM MDT Mon Apr 30 2018 A mixture of rain and snow will continue today and then turn to mostly all snow by tonight. By Monday night, snowfall accumulations of an inch could occur in the Cody area. As much as 2 to 4 inches of snowfall could occur in a band from the higher elevations of the Cody Foothills, southeast to along the Owl Creek Mountains. Roads may become slushy or snow covered by tonight over the higher elevations of the Cody Foothills. WYZ001-013-024-025-302100- Yellowstone National Park-Jackson Hole- Salt River and Wyoming Ranges-Upper Green River Basin Foothills- Including the cities of Lake, Mammoth, Old Faithful, Jackson, and Pinedale 104 AM MDT Mon Apr 30 2018 A mix of rain and snow will occur in the Jackson Valley today with snow in the mountains. Expect accumulations of 3 to 6 inches in the mountains. In the Jackson Valley, 1 to 3 inches of snow will fall, mainly north of the Jackson Hole Airport. Salt Pass will likely become slick and snow covered today and tonight.
The national radar mosaic for the moment the first event began.
2 winter storm. Local standard time, as filed.
The Deer Park SNOTEL site had 17 inches of new snow. There was 12 inches of new snow at the South Pass SNOTEL site.
The Marquette SNOTEL site received 14 inches of new snow.
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, April 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: 748474, 748475.