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Updated at 4:34 p.m. ET

As weary travelers make their post-Thanksgiving trek back home — and back to work — two winter storms continue to disrupt travel plans throughout the nation. Heavy snow and ice accumulation is expected to continue battering regions across the United States on Sunday, the first day of meteorological winter, delaying or cancelling flights of thousands of customers.

The said the inclement weather stems from a powerful transcontinental storm that has hammered the western U.S. During Thanksgiving, it moved east and is now expected to bring up to 12 inches of snow to parts of the Great Lakes region.

The hazardous storm is likely to shift into New England states by late Sunday and develop into a nor'easter, according to Lara Pagano, a meteorologist for the NWS.

"We're seeing values upwards of 8 to 12 inches and even along the Catskills and higher terrain, we're seeing values upwards of towards 15 inches in that area," Pagano said regarding expected snowfall in New York and Maine.

More states, including Connecticut, Massachusetts and Vermont, are subject to a . Portions of Pennsylvania are being warned of dangerous ice accumulation occurring Sunday, which officials say will cause travel to be "nearly impossible."

According to and , the majority of snow accumulation will occur Monday night and Tuesday morning as the storm moves closer to the Atlantic Ocean.

The storm moves east after pummeling parts of the Upper Midwest. was recorded Saturday in Duluth, Minn., where nearly 20 inches of snow covered the city.

Meanwhile, a new system has formed over the West Coast, with weather officials describing it as "a slow moving storm over the eastern Pacific" that will " " as a plume of moisture moves inland.

As a result, parts of Northern California and Nevada are subject to winter storm watches or warnings. warned travelers of possible road closures and moderate to heavy snowfall over the Sierra Nevada through Monday.

Due to extreme weather, over 700 U.S. flights on Sunday have been cancelled and more than 4,500 have been delayed as of 4:35 p.m. ET according to flight tracking website .

Several airlines are offering waivers to customers caught in the winter storm. customers flying to New England Sunday or Monday to reschedule their flights free of charge. Delta announced waivers for 42 cities in the Northeast and Midwest Sunday, with 22 of those cities eligible for rescheduling Monday. will also waive fees dependent on customers' airport.

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