(CNN) Minnesota's known for being cold, but the southern part of the state froze over late Friday and early Saturday.

Overnight temperatures were hovering below freezing, said CNN meteorologist Gene Norman, but what was odd was that current temperatures in the state are warmer for this time of year.

"It's slightly unusual," Norman said, adding that the icing occurred because of a surge of warm air. "What's falling out of the sky, melts in a shallow layer above the ground and refreezes when it hits the ground."

So how cold is it in Minnesota? Well, it's so cold that ...

School buses are slipping and sliding on the roads