By Sophia Rosenbaum, Staff Writer, NBC News
A storm system brewing over the Midwest threatened tens of millions of people Wednesday with heavy rain, hail and perhaps even a derecho — a rare, explosive wind pattern that forecasters compare to the landfall of a hurricane.
Chicago, Detroit and Cleveland were all in the threat zone, with Pittsburgh, Baltimore and Washington at risk of severe storms on Thursday.
The system, the product of hot air streaming up from the south and atmospheric churning over Minnesota, was certain to bring ugly weather. Forecasters said it was trickier to predict whether it would produce the little-known phenomenon of a derecho.
“Conditions seem to be favorable for one this week. Maybe more than one,” said Nick Wiltgen, a meteorologist for The Weather Channel.
A derecho that struck last June caused 13 deaths and did $ 1 billion in damage.NBC’s Mike Viqueira reports.
Late Wednesday morning, the National Weather Service upgraded the likelihood of extreme weather and said there was high risk of damaging wind in Iowa, Illinois, Indiana and Ohio. Parts of Iowa and Illinois had a 15 percent chance of tornadoes.
A derecho can cause damage similar to a tornado but moves along a straighter line. (In Spanish, the term can mean “direct.”) To qualify, the swath of wind damage must be 240 miles long and include wind gusts of 58 mph or higher along most of its path.
Last June, a derecho packing wind of close to 100 mph roared from Illinois to the Mid-Atlantic, killing 13 people, causing $ 1 billion in damage and leaving more than 4 million people without power. That storm was followed by a heat wave that killed dozens more.
In July 2006, two derechos struck the St. Louis area two days apart. The first injured 30 people at Busch Stadium, where the Cardinals were getting ready to play the Atlanta Braves. Half a million people lost power.
And in July 2003, a derecho that tore a path from Memphis, Tenn., to Atlanta left hundreds of thousands of people without power, some for more than two weeks.
Tom Moore, another Weather Channel meteorologist, suggested that the storms Wednesday would not match last year’s “because it’s a much sloppier system.” But he said it would still bring widespread damage and localized flooding.
NBC Chicago warned that the storms could complicate travel for people attending Game 1 of the NHL’s Stanley Cup Finals, to be played in Chicago between the Blackhawks and Boston Bruins.
If a derecho does occur, it will probably form later Wednesday night and last until the early morning hours of Thursday, said Bill Karins, a meteorologist for MSNBC. But he stressed that forecasters were not sure.
“It’s like predicting a large tornado is going to happen,” he said. “No one can do that. The only thing we can do is say conditions are favorable for one to happen.”
This story was originally published on Wed Jun 12, 2013 9:45 AM EDT
Derecho feared in Midwest
