MINNEAPOLIS (AP) — Hundreds of schools across Minnesota have called off classes because of the dangerously cold temperatures.

Minneapolis Public Schools are among those deciding to close Wednesday. Temperatures across the state are well below zero. And, with the wind chill, those readings have dipped to 40 below at Bemidji and minus 29 in the Twin Cities.

Experts say the temperatures can cause frostbite on exposed skin in 10 to 20 minutes. The brisk wind can also cause a greater loss of body heat.

Forecasters say Thursday and Friday will continue to be bitterly cold. Thursday’s high temperature could hit 13 degrees, but it will drop back to single digits on Friday.