1) When there is an unusual amount of snow (over 1 foot) in a place that normally gets only a few inches a winter season. (ie: Washington, DC)
2) When there is a snow storm, and a day or 2 later, there is another snow storm.
3) the combination of snowpocalypse and snowmageddon
In the winter of 2010 there was a snowpocamageddon.
I can't believe it's a snowpocamageddon!