What's unusual about today is the winter storm that passed through the Southeast, Peronto said.
"The Southern states don't typically get significant snow amounts through the year," Peronto said. "It takes a special kind of weather scenario to allow that to happen."
Snow in the eastern third of the United States is particularly unusual this year because La Nina (unusually cold ocean temperatures in the Pacific near the equator) normally keeps the jet stream in the northern regions of the United States, said David Robinson, the state climatologist of New Jersey and a professor at Rutgers University.
But recently, the La Nina effect has been overshadowed by a negative North Atlantic Oscillation, an atmospheric pattern that brings cold and snow to the East and Southeast.
"If the North Atlantic Oscillation was what we call neutral or positive, we might have our lounge chairs out today," Robinson told LiveScience. [Read Q&A with Robinson About Wild Winter Weather]
Snow over time
Snow in so many states is "not an every-winter event," Robinson said, though the last time it snowed in all 50 states was last February. Before that, he said, you have to go back to the 1970s to find winters where snow fell across so much of the North American continent.