A massive storm heading out of the Rockies toward Massachusetts is expected to dump snow, sleet and freezing rain over Pennsylvania Tuesday and Wednesday.

Almost everyone knows what snow is, but the difference between sleet and freezing rain can be confusing.

The National Weather Service explains it: "The difference is where the precipitation freezes as it falls to the ground. If the temperature if above freezing (32 degrees Fahrenheit) all the way to the ground, it will rain.

On the contrary, if the temperature is freezing all the way to the ground, it will snow.

For sleet, the temperature in the cloud is above freezing but below freezing from the cloud to the ground, so ice pellets fall.

Freezing rain also has above-freezing cloud temperature, but this relatively warm layer extends almost to the ground, where the temperature switches to subfreezing, causing the rain to freeze after hitting the ground."