This time of the year all precipitation begins as snow. The snow leave the clouds and falls towards the earth. As the snow falls it travels through a warm layer of air (Air above 32 degrees) and melts to just plain rain. The rain then contiues to fall to earth until it travels through a cold pocket of air (Air below 32 degrees). The cold pocket of air is deep enough to allow the rain to refreeze into a ice pellet. This ice pellet is call sleet.