What causes a Winter Snow Storm?

> By Rachelle Oblack , Weather Expert

> Moisture is the first ingredient necessary to produce a

> winter storm. Moisture is water in air.

> Moisture in air comes from evaporation from lakes, riivers,

> seas, trees leaves.

> Although it may seem like common sense, temperatures must be

> below freezing not only in the clouds but also at

> the ground surface.

> Believe it or not, it can and does snow in the desert, but

> it never reaches the ground because of the high

> temperatures!

> When warm air meets with cold air warm air rises over

> the cold air.

> The boundary between the warm and cold air masses is called

> a front.

> Snowstorms happen when a mass of the warm air rises quickly

> and the cold air cuts underneath it.

> This leads to heavy snowfall.

> see attached picture of meeting two fronts.

> Also note that Warm air is lighter than the cold air.

> Therefore the warm air will always be over the cold

> air.