After a short break later in the morning, the system was expected to spread to New England and West Virginia from around 1 p.m.
While Sunday's storm covered one large area, Monday's bout of extreme weather was forecast to impact on two sections of the country. After its northern section batters the Northeast, the South was set to be slammed in the afternoon. Roth said strong straight-line winds were predicted to do damage from North Carolina across the Gulf Coast to New Orleans.
Tennessee was particularly hard hit by Sunday's storms. Four tornadoes were reported to the National Weather Service across the state—one of these could have been responsible for flattening 10 homes just north of Knoxville. Another tornado was confirmed in Wolcott, Connecticut, at 12:50 p.m., and another was reported but unconfirmed in Ritchie, West Virginia, just after 8 p.m.
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By 4 a.m. ET on Monday, 145 flights were canceled and 181 delayed across the U.S. and Canada, according to FlightStats.com. The worst affected airports were Philadelphia International and Detroit Metropolitan, both of which were in the path of the bad weather. On Sunday, there were more than 500 cancellations and nearly 7,000 delays nationwide.
Roth said the storms were unusual for this time of year. A cold front was moving south through Tennessee, while a warm front was barreling east, from Michigan to southern New England.
—By Alexander Smith and Tim Stelloh, NBC News