A potent area of low pressure passed to the south of Wyoming and brought very heavy snow to portions of Wyoming. The heaviest snow fell in a band through Lincoln, Sweetwater, Fremont and Natrona Counties.
Every event with a place to put it; 16 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.
A potent area of low pressure passed to the south of Wyoming and brought very heavy snow to portions of Wyoming. The heaviest snow fell in a band through Lincoln, Sweetwater, Fremont and Natrona Counties. The most notable snow was in Casper in Natrona County. Two snowfall records were broken. A storm total snowfall of 37.4 inches over 3 calendar days, April 3rd through April 5th, fell at the Casper airport. In addition, an all-time 1-calendar-day snowfall record was set on April 3rd with a 26.7 inches of snow. Both these numbers broke the old records which occurred during the December 23-24, 1982 snowstorm. Other notable snowfall amounts included 20 inches at Afton in Lincoln County, 60 inches of new snow on Casper Mountain and 19 inches in Green River in Sweetwater County. In Fremont County, 48 inches of new snow fell at Atlantic City in the Wind River Mountains. In the lower elevations, 7 to 11 inches of new snow fell around Riverton with up to 18 inches near Lander. The snow was accompanied by gusty wind in the favored locations which brought blizzard conditions at times. As a result of the heavy snow, most major roads in the central and southern portions of the state, including Interstates 25 and 80, where closed for multiple days during the storm. Many schools were closed or went to virtual learning during the height of the storm.
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 1, 10:29 PM MST, 1 hour 31 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1129 PM MDT Sat Apr 1 2023 .DISCUSSION...This Afternoon through Friday Issued at 204 PM MDT Sat Apr 1 2023 Satellite imagery depicting another round of Pacific moisture making its was across Idaho early Sunday afternoon. This next plume is riding a 120+kt jet ahead of a distinct shortwave seen in the Idaho Panhandle. These features combine to generate a period of more intense snowfall across the western mountains through Saturday evening. Strong mid-level winds exceeding 45kts continue to plague areas east of the Continental Divide, mainly central Wyoming, through the same timeframe. Both the western snow and eastern wind decline early Sunday morning as the shortwave tracks across the Canada/Montana border and swings a cold front through the state. This shunts much of the remaining moisture to southwest Wyoming and switches the wind to a less favorable west-northwest direction. High-resolution models continue to favor at least areas of light snow across Sweetwater County late tonight and early Sunday morning, and precipitation chances have been adjusted accordingly. The west-northwest flow favors a lingering 10-20 mph downslope breeze overnight. Lows Saturday night have been adjusted upward slightly to account for improved near-surface mixing. Persistent westerly flow results in continued orographic snow over the western mountains Sunday, but accumulations will only total 1 to 3 inches. The jet stream gradually begins to back to the southwest late in the day and Sunday night in response to a digging trough over the Pacific Northwest. This initially shifts the bulk of the western snow to the Salt River and Wyoming Ranges later Sunday afternoon. Plenty of wind continues across the southwest and east of the Continental Divide with 20 to 30 mph sustained speeds and gusts 35 to 40 mph common through the afternoon. Despite the passage of the Pacific front, temperatures will only drop three to five degrees given the persistent mixing thanks to the wind. Regardless, highs Sunday will still be running around 10 degrees below seasonal averages for early April. Sunday night marks a sharp transition to what is to be an active period to begin the work week. The jet backs more to the southwest and Pacific moisture begins to track across the Great Basin into southern Wyoming. Light snow should gradually increase and begin to spread north after midnight early Monday. For the most part, impacts should generally be confined to Sweetwater County and neighboring portions of Lincoln, Sublette, and southern Fremont counties. Low pressure begins to develop to our southwest during this time, which will begin to induce a northeasterly mid-level flow late in the night. Speeds will not increase appreciably yet, but the direction allows for colder air to slip south and will also favor upslope snow heading into Monday. Moisture continues to spread north Monday given a southwest flow aloft. A northeast 700mb wind steadily increases through the day in response to a developing mid-level circulation over northeast Utah. This sets the stage for overrunning precipitation across southwest and central Wyoming. Temperatures around 30F during the day may allow for less accumulation, at least on the roads, until the snow begins to come down heavier late in the day and Monday night. It is Monday night when conditions are expected to deteriorate substantially. Left-exit region jet dynamics combine with solid Q-vector forcing and favorable 700mb temperatures of -12C to -14C to generate a distinct 12-hour or so period of heavier snow. It is conceivable a jet streak off to our east may couple with the southwest jet to initially further enhance snowfall. The 700mb low tracks slowly along the Wyoming/Colorado border Monday night and snow should increase on the north side of this circulation. To add to the impacts, northeast surface wind further increases overnight with the potential for widespread near-blizzard or blizzard conditions from eastern Sweetwater County through southern Fremont County into Natrona County. This same area would also be favored for heavier snow given proximity to the 700mb low and the enhanced forcing on the north side of this circulation. There is some indication, particularly by the GFS, for the potential for strong downslope wind on the west side of the Wind River Range. This downslope hinders snowfall in Sublette County. Impacts from the snow and wind remain high through around midday Tuesday, after which time a surface low to our east begins to race across Nebraska. This should allow for a downward trend in snow production Tuesday afternoon. As the low pushes east, the gusty northeast wind gradually becomes more northerly Tuesday afternoon, but speeds do not completely taper off until late Tuesday night. Current projections are for widespread 8 to 12 inch totals with favored locations seeing 12 to perhaps 20 inches of snow. The eastern Bighorn Basin and the downsloped areas of Sublette County are likely to see the least snow. For now, will continue with winter storm watches and a few zones on the northern periphery of the storm have been added. For central and southern Wyoming, there is widespread 60 percent or better probabilities of at least 8 inches of snow, a number that rises to 80 percent in Natrona County. Upslope favored locations have a better than 50 percent chance of seeing 12 inches of snow. Overall, the snow and wind combination will lead to significant travel impacts, especially late Monday afternoon through Tuesday. Beyond the early week storm, cold northwest flow prevails Wednesday favoring orographic snow across the western mountains. Otherwise, the trend will be toward a drier, westerly flow to end the week. Unseasonably cold temperatures persist through Thursday with highs 15 to 25 degrees below normal. Readings do appear to moderate heading into next weekend, with cluster analysis giving perhaps a hint of a western ridge by next Saturday. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1128 PM MDT Sat Apr 1 2023 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals An active TAF period is expected. Light snow continues at KJAC tonight, increasing in intensity from sunrise to sunset. During that time, IFR conditions are expected. Conditions improve to MVFR Sunday evening, with light snow persisting. Light snow begins at KBPI and KPNA this afternoon and drops conditions to MVFR/IFR through Sunday evening. An area of light snow may develop over KRKS around 08Z tonight, which should drop conditions to MVFR until sunrise. Then VCSH will hang around through Sunday afternoon before steadier snow moves in late Sunday evening. Wind will be elevated at KRKS and KJAC through Sunday afternoon, with gusts of 20 to 30 knots. Wind increases at KBPI and KPNA Sunday afternoon. Mountains will remain obscured over the next 24 hours. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals Conditions will remain VFR through Sunday evening at all terminals. Wind will be elevated at all terminals Sunday afternoon, subsiding by sunset Sunday evening. Gusts of 25 to 35 mph from the southwest will be frequent at KCPR for the first half of the TAF period, subsiding around sunset Sunday. Ceilings will start to lower toward the end of the TAF period as the next weather system pushes into the area. Light snow will begin to impact KCPR, KRIW, and KLND Sunday night just beyond this period. Mountain obscuration will be possible beginning Sunday evening. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 204 PM MDT Sat Apr 1 2023 Strong westerly flow aloft will generate very windy conditions over much of the forecast areas through Sunday. The strongest wind occurs in central Wyoming through Saturday night. Conditions remain dry east of the Continental Divide through Sunday. The westerly flow also keeps snow ongoing across the western mountains through at least Sunday morning before slowing a bit as the upper flow backs to the southwest. This gradually shifts snow to the southwest mountains late Sunday before spreading into southern Wyoming Sunday night. The snow becomes heavier and more widespread over all but the northwest corner of the state Monday and Monday night. This system has the potential to produce significant snowfall across most of the Casper Dispatch area and possibly the far southern Bighorn Basin by sunrise Tuesday. Even locations over the northwest and far north are likely to see snow accumulations of at least a few inches. Gusty north to northeast wind of 15 to 30 mph will be common. However, a corridor from Natrona County to eastern Sweetwater County, could see 30 to 45 mph northeast wind at times in conjunction with the snow. Smoke dispersal will be best Sunday afternoon given warmer temperatures and the continued strong transport wind. The snow hampers dispersal Monday and Tuesday. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 6 AM MDT Sunday for WYZ001-012. Winter Weather Advisory until 6 AM MDT Sunday for WYZ002-013-014- 024. Winter Storm Watch from Monday afternoon through Tuesday afternoon for WYZ009>011. Winter Storm Watch from Sunday evening through Tuesday afternoon for WYZ014-015-019-026>030. Winter Storm Watch from Monday morning through Tuesday afternoon for WYZ017-018-020-022. && DISCUSSION...CNJ AVIATION...Rowe FIRE WEATHER...CNJ
Hazardous Weather Outlook National Weather Service Riverton WY 226 PM MDT Sat Apr 1 2023 WYZ001>020-022>030-021300- 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- 226 PM MDT Sat Apr 1 2023 ...Multiple Winter Weather Highlights Remain in Effect... ...High Wind Warnings Continue for Portions of Central Wyoming through This Evening... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Moderate to heavy snow falls in the western mountains this evening before decreasing early Sunday. Strong wind from around Casper to the east slopes of the Wind River Range persist through the evening before slowing after midnight Sunday. Please see the High Wind Warning and other winter weather highlights for additional details. .DAYS TWO THROUGH SEVEN...Sunday through Friday. Sunday...Light snow continues across the west, while the east remains windy. Some travel impacts possible. Monday and Tuesday...Increasing snow across the south early Monday, spreading into central Wyoming Monday morning. Moderate to heavy snow is possible in these areas through Monday night. A gusty northeast wind of 20 to 40 mph could create near white-out conditions at times. Light to moderate snow expected elsewhere. Unseasonably cold. Wednesday and Thursday...High temperatures 15 to 25 degrees below normal. .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.
13 winter storm, 3 blizzard. Local standard time, as filed.
Heavy snow fell in southern Lincoln County, including 22.8 inches of new snow near the Fossil Butte National Monument site.
Many locations in the Star Valley reported over a foot of new snow, including 22 inches of new snow in Afton.
Very heavy snow fell through much of Rock Springs and Green River, with amounts ranging from 12 to 20 inches.
Very heavy snow fell along the eastern slopes of the Wind River Range. The heaviest snow fell at Atlantic City where 4 feet of new snow fell over 48 hour period. Many SNOTEL locations reported more than 3 feet of new snow.
New snowfall amounts around the Lander Foothills generally ranged from 8 to 18 inches, with the highest amounts in the foothills closer to the Wind River Mountains.
An observer reported 7 inches of new snow near Farson.
A record setting snowstorm occurred in Casper. Both daily and storm record snowfall records were broken at Casper. All areas of Casper received at least 2 feet of snow with a maximum of almost 40 inches on the south side of Casper. Amounts dropped further west and north with 14 inches near Powder River and 7 inches at Midwest. The heavy snow combined with gusty wind resulted in nearly impossible travel conditions for several days. A storm total snowfall of 37.4 inches over 3 calendar days fell at the Casper Airport, April 3rd through April 5th. In addition, an all-time 1-calendar-day snowfall record was set on April 3rd with a 26.7 inches of snow.
Very heavy snow fell on Casper Mountain, with a maximum amount of 5 feet.
New snowfall amounts around the Wind River Basin ranged from 7 inches at Hudson to 10.5 inches at the National Weather Service office to the northwest of Riverton.
Locally heavy snow fell to the west of Thermopolis, with 7 inches of snow near Hamilton Dome. Amounts dropped sharply from Thermopolis and eastward.
Heavy snow combined with frequent wind gusts over 40 mph to bring blizzard conditions to portions of Natrona County, bringing road closures and nearly impossible travel conditions.
Snowfall amounts in northern Johnson County ranged from 6 to 9 inches.
A CocoRaHS observer reported 7.5 inches of snow to the northeast of Mayoworth.
To the southeast of Big Trails, 15 inches of new snow fell.
Heavy snowfall amounts up to 20 inches combined with winds gusts up to 60 mph to bring an extended period of blizzard conditions. Interstate 80 was shut down for several days with many people having to be rescued from stranded vehicles. Travel was nearly impossible through the period.
A combination of heavy snow and strong, gusty wind brought blizzard conditions to the Green and Rattlesnake Ranges. As a result, numerous roads were closed for several days, making transportation nearly impossible.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2023Every state in 2023This day in weather historyWarnings in Wyoming, April 2023
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: 1096757, 1096758, 1096761, 1096750, 1096751, 1096760, 1096764, 1096766, 1096752, 1096754, 1096765, 1096755, 1096756, 1096759, 1096763, 1096753.