An abnormally cold low pressure system brought locally heavy snow to some of the mountains of central Wyoming. In the Bighorn Mountains, 20 inches of new snow fell at the Cloud Peak and Little Goose SNOTEL sites.
Every event with a place to put it; 2 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.
An abnormally cold low pressure system brought locally heavy snow to some of the mountains of central Wyoming. In the Bighorn Mountains, 20 inches of new snow fell at the Cloud Peak and Little Goose SNOTEL sites. At Casper Mountain, 16 inches of snow was reported.
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 May 21, 10:49 AM MST, 11 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1149 AM MDT Tue May 21 2019 .SHORT TERM...(Today through Thursday night) The main 500mb low is currently spinning over the Four Corners Region at the moment. A stationary sfc boundary remains along the Divide of Wyoming. Southwest of the sfc boundary, an occasional flare up of convection with isolated lightning has been taking place, with just left over showers on the other side of the boundary. The main 500mb low will redevelop as cyclogenesis takes place over Southeast Colorado by 12Z this morning. This will set us up for another round of a cold stratiform precipitation event, mainly east of the Divide. The heaviest precipitation will take place across Natrona and Johnson Counties today and tonight where the heaviest wrap around precip will occur as the low tracks north along the Plains states. Although the heaviest purely “wrap around” precip will likely take place in Johnson County, the upslope that occurs around the Casper/Casper Mountain area will balance out the amounts. The NAM indicates -9.5C temps wrapping around into Johnson County and -8C over Natrona County. With the amplified QPF of a half to three quarters and sufficiently cold temperatures at 700mb, we will include the lower elevations of Natrona and Johnson Counties for a late May Winter Weather Advisory along with the East Slopes of the Wind River and Big Horn Mtns as well as Casper Mountain. However, we will not start the low elevation advisories until 00Z Wednesday. All the advisories will end at 18Z Wednesday. The mountains will actually witness warning amounts, but with the minimal impact and strong May sun interacting with the snowfall this afternoon, will keep these mountain zones in an advisory, which, by the way, began at 06Z this morning. The mountain advisories will also go through 18Z Wednesday. The only missing element will be the wrap around isentropic lift that the earlier model runs were indicating. The least amount of precip from this event will occur west of the Divide over Northwest Wyoming, farthest away from the low, and where downslope flow will occur. Snow levels west of the divide should run about 6K. After 18Z Wednesday, the back edge of the precip will gradually push off to the north to our northern zones. The least amount of precip anywhere across the CWA will likely take place between 00Z and 06Z this evening as one batch of precip exits to the north and the next large area of precip moves in from the south. This next area of precip will be associated with the kicker that is now approaching the Pacific Northwest and is progged to be located over the Great Basin by Thursday, as both this low and the exiting low “dumbbell” around each other. This large glob of precip will rapidly shift north, mainly across the east half of the CWA Thursday, given the strong southerly difluent flow once again ahead of the low, which will track to Northwest and Northern Wyoming by the models by Thursday night, along with the associated strong QG forcing. The precip will taper off in intensity during the night Thursday night. Snow levels with this weather system should run about 6k east of the Divide and 7500 feet west. Any thunderstorms that occur through Thursday will be relegated to a few isolated afternoon storms west of the Divide through Thursday. .LONG TERM...(Friday through Tuesday) The first part of the forecast should feature a general decrease in activity across the area. The upper level low that brings the precipitation for Thursday will have lifted north of the state by that time. Enough wrap around moisture may be present for a few showers and thunderstorms, mainly of the afternoon variety, on Friday but these would be confined to the west and northern portions of the area and even here most of the day should turn out to be largely rain free. We may even see some glimpses of that round orb in the sky. What is that thing called? Oh yeah, the sun. Temperatures will turn much milder as well, but still be below normal. Transitory ridging will build over the state for Saturday. At this point, this looks to be the least active of the extended period. For the most part, we kept POPs in the chance of less range with areas East of the Divide largely dry. The GFS is wetter but tends to have a wet bias this far out as well as a fast bias so we went closer to the European guidance. As the ridge shifts to the east of the area and an upper level low tries to approach from the south and west, convection will again become a little more numerous although it should remain largely diurnal on Sunday and Monday with a good portion of each day rain free. Temperatures will continue to slowly moderate but will remain near to somewhat below normal for most locations. Tuesday at this point may turn out to be the most active day but still a && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1145 AM MDT Tue May 21 2019 Large low pressure system currently extends from southeast WY to northeast CO, primarily bringing very moist northerly and easterly flow to eastern and central WY. LIFR to MVFR conditions continue at terminals east of the divide as well as KRKS, with VFR across western WY. Primary band of snow extending from north to south across central WY will move slowly westward and become more showery over the next couple of hours. Isolated thunderstorms are possible over far southwest WY through the afternoon. Terminals east of the divide will see a brief respite in precipitation for a few hours, though IFR conditions likely to continue. LIFR expected to return to KBYG and KCPR by 02Z/Wed, and back to KRIW/KLND/KWRL/KCOD around 06Z/Wed. Western WY terminals may see MVFR under showers through 04Z/Wed. Northeast winds could gust over 20 mph in the forecast period. LIFR/IFR conditions to continue at terminals east of the divide through 18Z/Wed at least as low pressure system moves to the northern Plains. Terminals west of the divide expected to be MVFR to VFR after 12Z/Wed with continued easterly flow. Mountains to remain obscured through the forecast period. Please refer to Aviation Weather Center products for more information on icing and turbulence forecasts. && .FIRE WEATHER... Cool and wet weather will persist through Thursday with the most precipitation and coldest weather to occur east of the Divide. Significant snowfall will occur in zones 280, 281, 285, 288, and 300, east of the Divide through Wednesday morning. An isolated thunderstorm is possible west of the Divide through Thursday. Smoke dispersal this afternoon will range from fair to good. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until noon MDT Wednesday for WYZ009>011- 015-020-022. && SHORT TERM...Lipson LONG TERM...Hattings AVIATION...McDonald FIRE WEATHER...Lipson
Hazardous Weather Outlook National Weather Service Riverton WY 244 AM MDT Tue May 21 2019 WYZ001>020-022>030-220845- 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- 244 AM MDT Tue May 21 2019 ...Winter Weather Advisory for Johnson, Natrona and portions of Fremont Counties... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Snow becoming more widespread, especially tonight. Please see winter weather products and forecasts for details. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Wednesday...Snow continuing, then gradually tapering off in the afternoon and evening. Another strong storm is expected to move through the area on Thursday as well. Temperatures will remain well below normal through at least Friday. Saturday through Monday.. Isolated mainly afternoon and evening showers and thunderstorms. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions, especially snowfall and any flooding. McDonald
Special Weather Statement National Weather Service Riverton WY 736 AM MDT Tue May 21 2019 WYZ017-018-211900- Wind River Basin-Lander Foothills- Including the cities of Riverton, Shoshoni, and Lander 736 AM MDT Tue May 21 2019 ...Snow and fog through around noon... Rain has changed over to snow in many locations of the Wind River Basin this morning as the next storm impacts Wyoming. Visibilities will be low this morning with moderate snowfall and patchy fog during the morning commute. The snow should taper off around noon and likely switch back to rain showers this afternoon. * WHAT...Snow and fog. Snow accumulations of 1-3 inches are possible, depending on elevation and surface. Fog and moderate snow fall could limit visibilities to one quarter mile or less. * WHERE...Wind River Basin, including Riverton, Lander, Fort Washakie, and Shoshoni. * WHEN...This morning from 700 AM through noon * ADDITIONAL DETAILS...Travel on local highways and roads could be difficult due to slushy on roadways and low visibilities due to moderate snowfall and fog. McDonald
Special Weather Statement National Weather Service Riverton WY 744 AM MDT Tue May 21 2019 WYZ030-211900- East Sweetwater County- Including the city of Wamsutter 744 AM MDT Tue May 21 2019 ...Snow and fog through around noon... Rain and snow will continue this morning across the eastern half of Sweetwater County due to the latest storm to impact the area. Rain, snow, and fog will limit visibilities for the morning commute and travel this morning through around noon. Precipitation should taper off mid day, though areas of patchy fog could remain. * WHAT...Rain, snow, and fog. Snow accumulations of 1-2 inches are possible, depending on elevation and surface. fog could limit visibilities to one quarter mile or less. * WHERE...Eastern Sweetwater County. * WHEN...This morning from 700 AM through noon. * ADDITIONAL DETAILS...Travel on local highways and Interstate 80 could be difficult due to moderate precipitation, slush on the road surface, and low visibilities. Please reduce speed and use caution. McDonald
The national radar mosaic for the moment the first event began.
1 winter storm, 1 avalanche. Local standard time, as filed.
The Cloud Peak and Little Goose SNOTEL sites had 20 inches of new snow.
At the Casper Mountain SNOTEL site, 16 inches of new snow was reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2019Every state in 2019This day in weather historyWarnings in Wyoming, May 2019
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: 822425, 822429.