Severe weather likely tonight, could become a derecho

Severe weather is expected in Missouri tonight, and now the National Weather Service is concerned storms could come together to form a derecho.

This graphic from the National Weather Service shows the potential threats from severe weather tonight.

A derecho is a long-lived, widespread, straight line wind storm. Such events have drawn national media attention including last week, when a derecho that swept across several midwestern states caused multiple tornadoes, heavy rain and widespread damage and has been blamed for five deaths and numerous injuries.

Meteorologist Mike July stresses that the formation of such a storm is possible and not definite.  Whether a derecho forms or not, severe weather is likely, and he wants Missourians to be prepared.

“Continue to monitor your local media because storms haven’t formed yet, and once they begin to form we’ll kind of see how they evolve,” says July. “If they begin to show signs that we look for, then we’ll have to maybe ramp things up a little bit.”

If the system evolves as some computer models say it will, it could produce winds of 70 miles per hour or more.

“Right now we’re kind of thinking in excess of 75 miles an hour winds are certainly possible, and it’s highlighted from an area southeast of Nebraska all the way over to St. Louis, so it’s a fairly wide corridor,” says July.

The public can often be dismissive of straight-line winds as a threat, but a prolonged straight-line wind even can be as damaging or more so than a tornado.

“In a tornado, if you kind of think of it in real estate coverage, it’s a small area that it covers,” says July. “If you’re talking about a true derecho, it could very well be, from the north end to the south end, it could be 100 to 200 miles long, and along that entire length you’re getting damaging winds.”

There is also a threat of flash flooding.

“We’re talking about one to three inches of rain possibly, and even from a localized area, four inches of rain,” says July. “We have multiple hazards to be concerned about this evening.