 The weather forecasters said it might snow tonight, or rain, or sleet? Why don't they know for sure if tomorrow will be a snow day? Predicting what form precipitation will take is actually pretty tricky. As precipitation falls thousands of feet, it can encounter air at different temperatures that change its form. Because water freezes at 32 degrees Fahrenheit, 0 degrees Celsius, if the temperature rises or falls just a few degrees, it changes the type of precipitation. If the air temperature between cloud and ground is 34 degrees Fahrenheit, that means rain. Just a few degrees colder might mean a snow day. Hooray!