Below freezing temperatures in the clouds and near the ground are necessary to make snow and/or ice.
Moisture forms clouds and precipitation. Air blowing across a large body of water such as the ocean or a large lake is an excellent source of moisture.
The moist air is then lifted to 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. The boundary between the warm and cold air masses is called a front.