Look at the below, mid afternoon temperature map of Minnesota on 3-27-02. Notice the temps are about 10 degrees cooler through the central portion of the state? It's not clouds or precip. that's keeping the temps down but rather, snow cover. The picture on the right is a visible satellite image taken of the same area on 3-27-02. The white, is snow on the ground, which closely matches the temperature map on the left.