Sleet forms when snow melts near 5000 feet but refreezes before it hits the ground. Upon close examination, one can usually see the remnants of the parent snowflake that was melted to form the snow pellet. Sleet and snow pellets often occur during major Winter storms when the atmosphere is near freezing on the eastern edge of the storm. One of the major dangers of Winter storms is wind. Wind transports moisture into the storm at the surface and aloft which allows the storm to intensify and continue unabated.
Wind can also create life-threatening conditions.
White-out conditions occur most often with major storms that produce a drier, more powdery snow. If you encounter white-out conditions, you should reduce your speed considerably until conditions improve or find a safe place to pull off of the road and remain there until the storm ends. A safe place is one that does not obstruct traffic, like a parking lot of a filling station. Wind driven snow can also result in drifting snow. Snow drifts can close roads when large enough, but there are other hidden dangers in snow drifts.