A large swath of the US Midwest has been blanketed with snow, forcing mass cancellations of flights and road closures.
Blizzard conditions developed in Chicago - where more than 30 centimetres of snow was expected by evening - and other Midwest centres on Sunday as the system slowly crept eastward into Pennsylvania and western New York state.
Parts of the New England region still digging out from a storm early last week were also readying for another round of snow to arrive and last through Monday.
The storm was expected to be the most far-reaching of the season, stretching from Nebraska to Maine, according to the National Weather Service.
Forecasters also said it was moving unusually slowly, meaning accumulations of between 25 and 40 centimetres of snow were possible for parts of Illinois, Indiana and Ohio.
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More than 1950 flights were cancelled in the Midwest, the vast majority in or out of Chicago's two airports.
Wind gusts in excess of 70km/h were also forecast, making road travel tricky. Illinois Governor Bruce Rauner cautioned against any travel and put state agencies on alert.
In Nebraska, several sections of Interstate 80 were closed on Sunday due to accidents in icy conditions.
The weather also led to power outages for roughly 18,000 ComEd customers in Illinois, most of them in Chicago.
The weather cut power to nearly 8000 northern Indiana homes and businesses.
The most intense period of snow in the Midwest was expected to hit on Sunday evening, meaning treacherous roads for those heading to Super Bowl parties.
Several of the Chicago area's top tourist attractions closed early because, including the Shedd Aquarium, Adler Planetarium and Brookfield Zoo.
The city's pizzerias, though, were expecting heavy demand for deliveries during the game and bars hosting Super Bowl parties said they wouldn't let the weather spoil their plans.
