Extreme Cold/Wind Chill in Shirley Basin, Wyoming

Overnight low temperatures fell to as low as -31 F from 12/21 into 12/22, with daytime highs generally remaining below -15 F during the afternoon on 12/22. Sustained winds 15-25 MPH resulted in a prolonged period of extreme wind chills under -30 F. The most extreme wind chills occurred between 6:00 PM MST on 12/21 and 12:00 PM MST on 12/22. Minimum observed wind chill values reached -61 F at WY44 (Shirley Rim, 2 NW of Shirley Basin) at multiple times between 5:22 AM and 8:36 AM MST on 12/22.

An intense arctic cold front tracked rapidly from north to south across southeast Wyoming during the morning and afternoon hours on 12/21. Temperatures at the Cheyenne Airport (KCYS) fell from 43 to 7 degrees between 1:05 PM and 1:18 PM MST, before plummeting to a near-record -25 degrees F at 7:15 AM MST on 12/22. Numerous records were set for the most rapid and extreme temperature drops in history. Morning low temperatures fell to -20 to -40 degrees F across a large portion of southeast Wyoming on 12/22, with many sites remaining below zero through the day. Wind chills plummeted to between -45 and -65 degrees F for many. The cold frontal passage on 12/21 was also accompanied by scattered snow showers and locally intense snow squalls, resulting in a period of extremely low visibilities and dangerous travel conditions due to a flash freeze. Several inches of mountain snow were also recorded in the Snowy and Sierra Madre mountain ranges, along with reports of significant blowing and drifting snow.