An unusually cold air mass dropped southward behind a cold front that moved across Wyoming. The front combined with ample moisture as well as strong mid and upper levels winds to bring an historic early season storm to much of western and central Wyoming. Many areas East of the Continental Divide, especially in the higher elevations and adjacent foothills, saw large amounts of snow. The highest amounts fell in the Wind River Range and Casper Mountain where up to 18 inches of new snow fell. Many areas around Casper and Lander, Wyoming, saw up to a foot of snow. The heavy, wet snow fell on trees with full foliage and brought down branches, limbs and in some cases entire trees. The trees fell on power lines causing numerous power outages. In western and southern Wyoming, wind was the main hazard. The strongest winds occurred in Sweetwater County, with wind gusts as high as 86 mph reported at the Rock Springs airport. Numerous trees were downed in Rock Springs and Green River, leading to thousands losing power. Portions of Teton and Sublette Counties also saw widespread tree damage and loss of power.

Winter Storm in ABSAROKA MOUNTAINS, WYOMING
From 07-SEP-20 15:00:00 to 08-SEP-20 09:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SNOTEL

The Timber Creek SNOTEL site recorded 12 inches of snow.

Winter Storm in NATRONA COUNTY LOWER ELEVATIONS, WYOMING
From 07-SEP-20 18:00:00 to 08-SEP-20 10:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy snow fell throughout Natrona County, including 7.5 inches at the Casper Airport. The highest amount occurred on the south side of Casper near Casper Mountain, where over a foot of snow fell. The snow fell on trees with full foliage and combined with gusty north winds brought down numerous limbs that led to almost 3000 customers to lose power.

Winter Storm in CASPER MOUNTAIN, WYOMING
From 07-SEP-20 15:00:00 to 08-SEP-20 11:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SHAVE Project

Heavy snow fell on Casper Mountain, including 16 inches at the Reno Hill SNOTEL site.

Winter Storm in WIND RIVER MOUNTAINS EAST, WYOMING
From 07-SEP-20 18:00:00 to 08-SEP-20 13:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SNOTEL

Heavy snow fell in the Wind River Mountains. Some notable amounts included 17 inches at the Cold Springs SNOTEL and 16 inches at Bruce's Campground.

Winter Storm in EAST SWEETWATER COUNTY, WYOMING
From 07-SEP-20 19:00:00 to 08-SEP-20 14:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A combination of snow and winds gusting to hurricane force brought nearly impossible travel conditions to eastern Sweetwater County. Winds gusted as high as 86 mph at the Sweetwater County airport. Interstate 80 was closed for a time during the height of the storm.

High Wind in WIND RIVER MOUNTAINS WEST, WYOMING
From 07-SEP-20 17:00:00 to 08-SEP-20 12:00:00 (MST-7)
Magnitude: 65.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The Sublette County emergency manager reported thousands of trees down throughout the western slopes of the Wind River Range.

High Wind in TETON & GROS VENTRE MOUNTAINS, WYOMING
From 07-SEP-20 17:00:00 to 08-SEP-20 06:00:00 (MST-7)
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

High winds downed many trees in Grand Teton National Park. Power was lost to many portions of the park with trails closed and some campers stranded in camp sites as roads were closed due to downed trees.

Winter Storm in CODY FOOTHILLS, WYOMING
From 07-SEP-20 17:00:00 to 08-SEP-20 06:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Near Meeteetse, Wyoming, 11 inches of new snow fell. Amounts dropped rapidly further north, with anywhere from 1 to 3 inches near Cody, Wyoming.

High Wind in JACKSON HOLE, WYOMING
From 07-SEP-20 17:00:00 to 08-SEP-20 03:00:00 (MST-7)
Magnitude: 61.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A strong cold front dropped through the Jackson Valley and mixed very strong mid level winds to the surface. The result was hundreds of trees downed through the area. Many subdivisions lost power for several hours in the surrounding areas. Trees were also downed in the city of Jackson, Wyoming, with the worst hit area near Albertson's where over a dozen trees were downed.

Winter Storm in GREEN MOUNTAINS & RATTLESNAKE RANGE, WYOMING
From 07-SEP-20 18:00:00 to 08-SEP-20 12:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

In the Jeffrey City, Wyoming area, 7 to 10 inches of snow fell.

Winter Storm in LANDER FOOTHILLS, WYOMING
From 07-SEP-20 18:00:00 to 08-SEP-20 12:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy snow fell in portions of the Lander Foothills. The highest amounts were closer to the Wind River Mountains with over 10 inches in some locations. At the Lander, Wyoming Airport, 4.7 inches of snow fell. The snow fell on trees with full foliage and the result were downed limbs and in some cases entire trees. Over 600 customers were without power for a time.

High Wind in UPPER GREEN RIVER BASIN FOOTHILLS, WYOMING
From 07-SEP-20 18:00:00 to 08-SEP-20 13:00:00 (MST-7)
Magnitude: 71.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The Sublette County Emergency Manager reported dozens of trees downed throughout the area. A messaging sign was blown down east of Pinedale, Wyoming. The sign was rated to withstand 82 mph wind gusts.

High Wind in UPPER GREEN RIVER BASIN, WYOMING
From 07-SEP-20 18:30:00 to 08-SEP-20 03:30:00 (MST-7)
Magnitude: 59.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Wind gusts as high as 68 mph were reported in Farson, Wyoming. Some power lines were downed, leading to localized power outages.

Winter Storm in ROCK SPRINGS & GREEN RIVER, WYOMING
From 07-SEP-20 19:00:00 to 08-SEP-20 15:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A tight pressure gradient and strong mid level winds mixed to the surface around Rock Springs and Green River, Wyoming. In addition, up to 7 inches of snow fell on trees that had full foliage. The result was widespread tree damage with large limbs and entire trees downed. At one point, almost the entire city of Green River along with much of Rock Springs, Wyoming was without power. Winds gusted as high as 67 mph in Green River at the height of the storm.