Holiday travelers — whether driving, flying or riding buses or trains to Christmas gatherings — may want to leave now rather than waiting until later in the week, when forecasters are predicting life-threatening conditions associated with an arctic blast that will blow into Minnesota and affect most of the Upper Midwest.

"Tuesday is definitely the best travel day of the week," said Bill Borghoff, a meteorologist with the National Weather Service in Chanhassen. By Thursday it may be next to impossible. Plan to change your travel plans. It's easier to change them now than later, and not risk trying to get where you are going," Borghoff said.

A polar air mass will drop 5 to 10 inches of fluffy snow on the metro area and much of Minnesota starting Tuesday night into Wednesday before the mercury sinks below zero. Sustained winds of 30 to 40 mph will blow the powder around, creating blizzard conditions that will last through Friday, particularly in western and southern Minnesota, Borghoff said.

A Winter Storm Watch was issued from Wednesday through late Friday night for all of central and southern Minnesota and west central Wisconsin, the Weather Service said.

High winds, which will reduce visibility even in the metro area, will also create dangerous wind-chill values as low as 35 below. That combination could make driving impossible and life-threatening for motorists who get stranded, Borghoff said.

"If you get stuck on the roads when it's below zero and windchills at minus 35, it does not take long to feel the effects," Borghoff said. "You will be in big-time trouble."

From Thursday through Jan. 2, AAA expects more than 8.1 million motorists to be on the roads in the North Central region, which includes Iowa, Kansas, Minnesota, Missouri, Nebraska and the Dakotas. People driving in those states this week are likely to encounter dangerous conditions, too.

"This is widespread," Borghoff said. "Heed warnings and road closures. We are taking this seriously and we hope others do as well."

The incoming storm has the potential to disrupt operations at Minneapolis-St. Paul International Airport, where Thursday and Monday are expected to be the busiest days. The airport has plows ready to keep runways clear and will have an eye on the sky.

"We will be watching it closely," said airport spokesman John Welbes.

Greyhound spokesman Sean Hanft said the company is preparing for a "potentially difficult holiday travel weekend throughout the U.S." He said the company will email passengers if their trips are changed. He also said riders can get updates on Greyhound's travel alerts page.

The Christmas week storm arrives just after a long-duration storm last week buried much of northern Minnesota under a couple feet of snow and knocked out power to thousands. The new storm won't bring a lot of snow but will keep Minnesota in a deep freeze through early next week, Borghoff said.

With the snow and bitter cold, "it will be nasty," Borghoff said.

The frigid air will plunge southward through this week, bringing freezing weather and windchills across the central, southern and eastern United States. By Friday night, the mercury will fall into the teens in Atlanta, with low temperatures flirting with the freezing mark in Orlando, the Storm Prediction Center said.