Besides "How much snow will I get?", one of the most common questions before a winter storm strikes often centers around whether your area will receive snow, sleet, freezing rain, or a combination of all three. Meteorologist at the National Weather Service continually investigate atmospheric data and computer model forecasts to forewarn you of any or all of these hazards.
You might be curious as to why one area may get snow, while another location just a half hour away is receiving freezing rain or plain rain. The key is in the temperatures within the atmosphere, specifically the temperature between the ground and the clouds above. The graphic below illustrates the following precipitation types.
Snow is produced when temperatures are cold both aloft and at the ground. The snow does not melt as it falls, and temperatures near or below 32 degrees near the ground allow it to accumulate.
Sleet is formed when temperatures at or slightly above freezing aloft produce rain that freezes to ice pellets, as it falls into a cold layer of air. Sleet usually bounces when hitting a surface and does not stick to objects. However, it can produce a “sandlike” accumulation like snow.
Freezing rain forms when warm temperatures aloft, generally several degrees above freezing, produces rain that falls onto a surface with temperatures below 32 degrees. This causes the liquid rain to freeze on impact to objects such as trees, power lines, cars and roads forming a coating or glaze of ice. Even a small amount of freezing rain on roads can create a significant travel hazard.
A day or two in advance of a storm, forecasters are usually confident with temperatures at the ground and at various heights above--within a few degrees. However, a difference as small as one or two degrees could mean the difference between snow, rain, or a mixture of freezing rain and sleet. Due to this uncertainty, it is sometimes difficult to pin down precipitation type too far in advance, especially if temperatures are expected to be right around freezing.
(Information for this page adapted from NWS Kansas City/Pleasant Hill and NWS Milwaukee/Sullivan.)