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    A slow-moving, upper-level disturbance moved from the southwest U.S. into southern Colorado then Nebraska from 8 March through 15 March, 2021. This disturbance strengthened on the weekend of 13-15 March and drew abundant moisture from the Gulf of Mexico which was transported to eastern Wyoming. The deep moisture combined with a strong east wind and instability wrapping around the north side of this disturbance resulted in a unique setup with strong lift occurring along and east of the Laramie Range. This resulted in anomalously high snowfall amounts from southern Johnson and Natrona counties near Casper Mountain, extending southeast along and east of the Laramie range, where this lift was maximized. Snowfall rates of 2 to 3 inches per hour occurred at times Saturday night, 13 March, and continued through midday Sunday, 14 March. Of note, 14 inches fell in a six hour time period from 6 AM MDT, Sunday, 14 March, to noon MDT at the Casper International Airport, and 10 inches of snow fell at NWS Cheyenne in a five hour period from 12am MST, Sunday, 14 March, to 6am MDT. Thundersnow was reported and observed several times across Laramie County during this time frame of the most intense snowfall rates. Snow to liquid water ratios were low on Saturday with values near 7 to 1 before midnight and increased to 12 to 1 after midnight into Sunday. This resulted in heavy, wet snow, followed by drier, more driftable snow. In addition, wind speeds increased to 45 to 55 mph and caused significant drifting. Due to the significant drifting, many area roads were closed for an extended period of time including Interstate 80 between Rawlins and Cheyenne and Interstate 25 between Casper and Cheyenne from Saturday night March 13th through Wednesday morning March 17th.





Tractors and heavy equipment continue to plow the Interstate 80 Summit around the clock to clear the 5+ foot drifts along the roadway. 

Credit: Wyoming Department of Transportation

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Reports of snow plows getting stuck on Sunday as the heavy wet snow and 50 MPH winds creating snow drifts made snow removal efforts nearly impossible for at time.

Credit: Wyoming Department of Transportation

Heavy equipment being used to clear snow from the Interstate 80 Summit all day Monday & Tuesday after the storm. 

Credit: Wyoming Department of Transportation

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