National Weather Service United States Department of Commerce

Low temperatures tonight and Tuesday night will be around 15 below to 30 below zero. Dangerous wind chills will bottom out around 25 below to 45 below zero, coldest across northwestern South Dakota. Some locations will have below zero temperatures from last night through Wednesday night. Frostbite can occur on exposed skin in as little as 10 minutes. Dress in layers and make sure to cover all exposed skin, including your head, face, and hands. Limit your time outdoors and bring your pets indoors. If traveling, bring a winter survival kit.
Light snow will fall through Tuesday. Additional snow accumulations will be 1 to 2 inches, especially from Gillette, Wyoming through the Black Hills into South Central South Dakota, which includes the Pine Ridge and Rosebud Reservations. Locally higher amounts may occur over far southwestern South Dakota. The snow, combined with bitterly cold temperatures will make for hazardous travel conditions.
The warnings signs of hypothermia are confusion, shivering, difficulty speaking, sleepiness, and stiff muscles. Go to weather.gov/safety/cold for additional safety information.