CLEVELAND (WJW) — A major winter weather event is already hitting part of the U.S. and will impact millions more through the Christmas weekend, meteorologists have confirmed.

The National Weather Service Weather Prediction Center has warned a storm system developing Wednesday night will “result in blizzard conditions across portions of the Central/Northern Plains, Upper Midwest, and Great Lakes.”

What exactly is the difference between a winter storm and a blizzard?

As Scott Sabol, a meteorologist at Nexstar’s WJW in Cleveland, OH explains, a blizzard is “three straight hours with winds at 35 mph sustained, not gusts” with falling and/or blowing snow that causes “visibility to drop under a quarter of a mile.”

The tidbit that may come as a surprise is snow does not have to be falling the entire time for a blizzard to occur and there is no specific temperature that must be hit to qualify.

A winter storm on the other hand, according to the NWS, is designated when any of the following is occurring or about to take place: Five inches or more of snow in a period of 12 hours or eight inches or more in 24 hours; there is so much ice that it causes tree and/or power line damage; or when ice, snow and wind combine to cause conditions the NWS considers damaging or life-threatening.

During both a blizzard and a winter storm, people are advised to stay off the roads and instead stay home, which could greatly impact holiday travel this weekend.

Regardless of whether you are hit by a blizzard or winter storm late this week and into the weekend, there’s a pretty good chance you’ll see below-freezing temperatures, forecasts from the NWS show.

Maps (seen here) show how the arctic blast will spread from northern states to the South as the week progresses.

For the latest weather updates, check out the WGN Weather blog.

Wednesday’s forecast shows frigid temperatures in the Upper Plains. From there, the sub-zero temperatures creep downward. By Thursday, the lows in Montana, for example, are as cold as negative 38 degrees.

It gets even colder Friday, when almost every state will see lows below freezing. On Saturday, Christmas Eve, the cold reaches the Gulf and East Coast. On Christmas, things start to get ever-so-slightly better. 

You can see just how cold it’ll get where you live here, and by staying up-to-date with your local weather experts.

For the latest weather updates, check out the WGN Weather blog.