Around 43 million Americans were at risk of severe thunderstorms that will sweep across the Plains before smashing their way into the Midwest on Monday, forecasters warned.
An area stretching from Minneapolis to Detroit — including Chicago — was facing damaging winds, large hail and potentially tornadoes, according to NBC News meteorologist Bill Karins.
"Damaging straight line winds are also a threat," said Kevin Roth, lead meteorologist at The Weather Channel.
After working their way over the Dakotas, Roth added there would be an "elevated tornado risk, primarily in southern Wisconsin and Michigan."
Ilinois, Iowa and Indiana could also see twisters and Roth expected more storm and tornado warnings to be issued throughout Monday.
"Very large hail" and flash flooding were also possible, according to the National Weather Service.
Roth said Tuesday will "be one hot day" for the Northeast, with highs in the 90s and potentially in the triple digits ahead of a strong cold front.
Record heat appeared possible for cities including Charlotte, North Carolina, and Washington, D.C., on Monday or Tuesday, according to Karins.
Temperatures will also soar to 20 to 30 degrees above average in the Northwest and northern Rockies, Roth said.
Meanwhile, Roth said firefighters battling a 17,000-acre wildfire in Southern California will not be aided by the weather as "there will be a zero percent chance of rain over the next 10 days."
The blaze, known as the Lake Fire has been burning for four days and is only 19 per cent contained, officials said Sunday.
However, there was better news for firefighters battling a 6,500-acre wildfire near Willow, Alaska. They will be aided with cooler conditions later this week, Roth said.