A severe weather outbreak was possible April 28 in the upper Midwest, forecasters warned, the first day of what could be a multiple-day siege of stormy weather over the central, eastern and southern states.
"The atmosphere will be very conducive for severe weather," the National Weather Service said.
A "widespread, significant" threat will develop, especially in the afternoon and evening, according to an online forecast from Weather.com meteorologist Chris Dolce.
Strong tornadoes, large hail and high winds are all possible dangers, the Storm Prediction Center said.