The same storm system hit Mexico earlier in the week, killing at least 29 people as heavy rains forced rivers to burst their banks and flood roads.
Parts of the country have received eight times more rain in the past four days than they normally get in a month.
"The storm in Mexico and the storm in the US are actually part and parcel of the same storm," Steff Gaulter, Al Jazeera's meteorologist, said.
"It started off over Mexico, then headed north over Texas and the southeast of the United States, and is now giving blizzards to the east coast.
Police said the severe weather led to the deaths of a father and son in Virginia on Friday, who were hit by a tractor-trailer while trying to help the driver of another vehicle on a busy highway.
Electricity has been cut to more than 120,000 homes and many offices in Washington DC - including Al Jazeera's broadcast centre - as power lines were knocked out by the powerful storm.
With winds gusting at almost 90km an hour, many places were already covered in more than 30cm of snow by early Saturday, including the White House grounds.
All flights out of the area's three main airports, meanwhile, have been cancelled, and the governors of Virginia, Maryland and Delaware have all declared states of emergency.
Bus services in the national capital were shut, as well as around 40 above-ground railway stations.
Residents in the affected areas have taken to referring to the storm online as a "snowpocalypse" or "snowmageddon", including on social networking site Twitterand Flickr- a photo-sharing website.
Officials, from the mayor of DC to the governor of Maryland, were on local TV and radio stations throughout the day on Friday warning people to stay home and off the roads.
Al Jazeera's Todd Baer, reporting from Washington DC, said that message resonated with a lot of people, who rushed to supermarkets before the snow started falling to stock up on food and other supplies.
"Most people had ample warning, and are prepared to handle this," he said.
"But for the people who have lost power in their homes, its unclear at the moment what they are doing, or how they are getting along."
Unseasonably cold temperatures were expected in the storm's wake next week in the northeast of the country.
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