Snow, Sleet and Freezing Rain
The Metro Area is often on the borderline between snow, sleet, freezing rain and rain when winter storms take shape. Depending on the storm track, we could see all snow, all rain or a wintry mix. This is because of the unique geography that exists in the Mid-Atlantic Region.
The truth is all precipitation falls from the clouds as ice crystals where temperatures are cold enough to support ice. In a "normal" atmosphere the temperature gets colder as you increase altitude. So in this case, the column of air that extends from the cloud to the ground remains below freezing the entire distance than the ice crystals will fall as snow. Even when surface temperatures are above freezing snow will still fall under the above circumstances. Snow is the easiest to deal with since it can be both plowed and shoveled.
If a portion of the column of air between the cloud and the ground is above freezing, than that presents a new host of problems. If there is a narrow column of air above freezing just above the ground, where temperatures are below freezing, than the ice crystals - or snowflakes - melt into raindrops but then freeze again when they come into contact with the ground creating freezing rain.
If the column of air with above freezing temperatures is higher above the ground than the flakes melt into water droplets and then refreeze into sleet before hitting the ground. Sleet can accumulate like snow, but tends to be heavier than snow because the water content is higher which suppresses accumulations. So, freezing rain falls as a liquid and freezes on contact with the ground, trees, power lines etc and sleet falls as a little ball of ice that bounces off your windshield.