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The exact timing of the approaching storm — and where it is headed — remained uncertain on Tuesday. Forecasters say it can be challenging to predict precisely which areas could see rain and which ones could be punished with ice.

Here’s what to know:

Cold air clashing with rain to fuel a 'major winter storm’

An extremely cold arctic air mass is set to dive south from Canada, setting up a clash with the cold temperatures and rain that will be streaming eastward across the southern U.S.

“This is extreme, even for this being the peak of winter,” ��ɫtv Weather Service meteorologist Bryan Jackson said of the cold temperatures.

When the cold air meets the rain, the likely result will be “a major winter storm with very impactful weather, with all the moisture coming up from the Gulf and encountering all this particularly cold air that’s spilling in,” Jackson said.

An atmospheric river could set up across the southern U.S.

An of moisture could be in place by the weekend, pulling precipitation across Texas and other states along the Gulf Coast and continuing across Georgia and the Carolinas, forecasters said.

“Global models are painting a concerning picture of what this weekend could look like, with an increasingly strong signal for ice storm potential across North Georgia and portions of central Georgia,” according to the ��ɫtv Weather Service's Atlanta office.

If significant accumulations of ice strike metro Atlanta, it could be a problem through the weekend since low temperatures early Monday are expected to be around 22 degrees (minus 5.6 Celsius) in Atlanta. The city's high temperature on Monday is forecast to be around 35 degrees (1.7 Celsius).

Highway and air travel could be tangled by the storm

Travel is a major concern, as southern states have less equipment to remove snow and ice from roads, and extremely cold temperatures expected after the storm could prevent ice from melting for several days. In Michigan, into each other or slid off an interstate southwest of Grand Rapids on Monday.

The storm is also expected to impact many of the nation’s major hub airports, including those in Dallas; Atlanta; Memphis, Tennessee; and Charlotte, North Carolina.

Polar air from Canada to keep northern states in a deep freeze

Unusually cold temperatures are already in place across much of the northern tier of the U.S., but the blast of arctic air expected later this week is “will be the coldest yet,” Jackson said.

“There’s a large sprawling vortex of low pressure centered over Hudson Bay,” Jackson said of the sea in northern Canada that’s connected to the Arctic Ocean. “And this is dominating the weather over all of North America.”

Texas could be a harbinger for other parts of the South

Some of the storm’s earliest impacts could be in Texas on Friday, as the arctic air mass slides south through much of the state, ��ɫtv Weather Service forecaster Sam Shamburger said in a briefing on the storm.

“At the same time, we’re expecting rain to move into much of the state,” Shamburger said.

Low temperatures could fall into the 20s or even the teens in parts of Texas by Saturday, with the potential for a wintery mix of weather in the northern part of the state.

Forecasters cautioned that significant uncertainty remains, particularly over how much ice or snow could fall across north and central Texas.

“It’s going to be a very difficult forecast,” Shamburger said.

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Panjwani reported from Washington, D.C.