We're at the time of year now when snow can turn the landscape white in a matter of minutes or hours. That transformation complicates the interpretation of satellite images, simply because both snow and clouds look white from space.

To a novice, there are a few simple ways to tell the difference between them on satellite images. First, a snowcover will end abruptly at the edge of a water body such as a lake or a river, but clouds won't. So a thin dark line snaking through a field of white on a satellite image is a river, and the white is snow, not clouds. This technique won't work, however, if the water bodies are frozen.

Another way to tell the difference between snow and clouds is by playing a movie of satellite images over a few hours. The clouds will usually move, but the snowcover won't.