46er....that a good link that everyone should read if they wish to spot a snowy.. Of the little I read, it is the lack of food source up north. It involves the population of lemmings that they feast on in Canada. A record number of nests have been detected this year.. The young owls are pushed father south in the winter to find food. Since they nest in open fields, that why they can be spotted at airports, farmland and along the coastline.
Actually it is an over abundance of food, i.e. Lemmings. They produce more eggs with abundant food and if the Lemming population then crashes, there are too many birds for the then existing food supply, hence their searches bring them south.
An excellent site for all things Owl below. Started by Denver Holt, it is one of the best sources of info, ton's of good info.