When March rolls around in Wisconsin and the temperature goes from 10 degrees to higher than 40 degrees. Wisconsin residents en masse are then seen in shorts, t-shirts, grilling out and throwing footballs around like it was 75 degrees and summer out. Since 40 degrees in the south would be considered oppressive weather and not "nice" it is referred to as Wisconsin Nice.
Robert: Get your shorts on everybody and get the ball, it is freakin' Wisconsin Nice out today!
Southern Man: Are you serious? It is 45 degrees out! I'll freeze!