PORTLAND, OR -- The 2015 snow pack was the lowest on record in Oregon, Washington and California. The region received a normal amount of precipitation; but, "It was exceptionally warm in Oregon; 6.5 degrees warmer than normal," says Phil Mote, Director of the Oregon Climate Change Research Institute. He adds, "That prevented the snow from falling down where it usually would."

Mote says greenhouse gases in the atmosphere are one reason. "In the case of an extremely warm winter, we do know that the extra heat-trapping gasses in the atmosphere probably made it a couple of degrees warmer than it would otherwise have been." The other factor, he says, was a "blob" of warm water in the Pacific Ocean.

This winter could go in the other direction. Mote says a La Niña appears to be forming in the Pacific, which could cause cooler temperatures and more snow.