Threat of violent storms and tornadoes to rise tonight across huge swath of Midwest and South
The severe weather that killed 32 people from the South to the Midwest over the weekend is gone, but another round of thunderstorms was aiming for nearly the same area Tuesday.
Federal forecasters said a thunderous front of wind, lightning, hail and rain, with fast-moving, strong and long-track tornadoes possible, will sweep into the eastern third of the country Tuesday afternoon and overnight into Wednesday.
The most violent storms are likely to happen after dark, making potential tornadoes twice as deadly as daytime twisters.
Severe storms are expected Tuesday and into the night across a large area stretching from the Great Lakes all the way down south to northern Texas. The storms will start earlier in the day in Iowa and Illinois, but not until around after midnight across portions of Oklahoma and Arkansas.
For the southern half of the risk area, the majority of the storms will happen at night. Large hail and winds in excess of 75 mph are all possible.
There's the added possibility that tornadoes as strong as EF-2, with sustained winds of 111 mph, could form as cold air from the north and warm, relatively wet air from the Gulf of Mexico clash explosively, forecasters said.
If strong winds aloft change direction and dive and supercells and then mesocyclones produce telltale vertical, thunderous and spinning storms, the system will have created fertile conditions for tornadoes, they said.
Cities most at risk for strong tornadoes includes Chicago, Detroit, Indianapolis and Toledo, Ohio.
"If they do form," National Weather Service meteorologist Melissa Byrd said of thunderstorms, "they have the potential for very large-scale and strong tornadoes."
An estimated 42 million are under the risk for severe storms Tuesday, according to NBC News' weather unit. That changes to around 62 million people on Wednesday, as the storm system stretches from northern Michigan to northern Louisiana.
The worst weather is likely to materialize along a vertical line from Des Moines, Iowa, to Little Rock, Arkansas, the National Weather Service said.
Springfield, Missouri, will join Iowa's Cedar Rapids, Davenport, Waterloo and Iowa City in being targeted for the worst of the front, which the weather service described as having a moderate risk of severe thunderstorms.
"Strong tornadoes and particularly damaging winds are expected," the weather service said in an outlook report Monday. "Both afternoon and overnight potential will exist across various regions, including the risk of dangerous nighttime tornadoes."
The largest city near the most intense weather predicted is St. Louis, where thunderstorms and even some tornado activity aren't unusual through May. But this time the region is being hammered.
"We can see possibly two rounds of severe weather — in the afternoon and through tomorrow night," said Byrd, based at the weather service office in nearby St. Charles.
North and west of that thunderstorm activity, in Wyoming, the Dakotas and Minnesota, the same front was expected to produce blizzard conditions and the possibility of record amounts of snow — as much as 2 feet in places — for April, according to the weather service and the NBC News weather unit.
Experts say the continental U.S. and the South in particular have the weather misfortune of being where cold fronts from Canada and Pacific storms move south and east and clash with tropical air from the Gulf of Mexico, creating an annual cauldron of stormy weather.
But climate change could be making the extremes worse, resulting in colder cold fronts, stronger tornadoes and bigger hailstones in spring, as well as longer, hotter streaks in summer, they have said.
In mid-March, the National Atmospheric and Oceanic Administration’s spring outlook called for moderate to major flooding from Minneapolis to St. Louis even as drought continued in the northern and central Plains.
"Climate change is driving both wet and dry extremes," NOAA Administrator Rick Spinrad said in the outlook.
