Moisture is the first ingredient necessary to produce a winter storm. Moisture makes the clouds that are capable of producing precipitation. Sources of moisture in the air can come from evaporative processes or air blowing across a body of water.
Although it may seem like common sense, temperatures must be below freezing in two locations to produce snow and/or ice. First temperatures at ground level must be freezing. This often causes accumulation. Next, temperatures in the clouds must also be freezing. Believe it or not, it can and does
snow in the desert, but it never reaches the ground because of the high temperatures!
The last ingredient necessary for a winter storm is lift. In this process, moist air is lifted form the clouds and cause precipitation. An example of lift is warm air colliding with cold air and being forced to rise over the cold dome. (Go to the cold and warm front tutorials
for more information.) The boundary between the warm and cold air masses is called a front. Another example of lift is air flowing up a mountain side.