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New Study Predicts Tornados and Hail During ‘Forecast Gap’
Researchers at Colorado State University studied a tropical weather pattern to learn how to better predict tornado and hail storms in the U.S.

Weather forecasters are good at predicting severe weather up to a week in advance. They're also pretty good at telling us what might happen three to six months from now.

But what about the time in between?

Research scientists at Colorado State University are learning how to predict thunderstorms on the Great Plains and southeastern U.S. that could lead to tornado and hail events two to five weeks out.

"In our community it's been called a forecast gap," said Cory Baggett, research scientist in atmospheric science.

In a new paper, the researchers studied the Madden-Julian Oscillation, an atmospheric phenomenon where a cluster of very large tropical rainstorms routinely travel around the equator. The tropical weather pattern sends out powerful atmospheric waves, and those ripples can reach the U.S. in a couple weeks, influencing severe weather in states like Colorado.

"It's been known to be a pretty decent predictor for weather across the United States," Baggett, the paper's lead author, said. "People have used it to forecast temperatures, precipitation, extreme rain storms like atmospheric rivers on the west coast."

The study looked at 37 years of data to examine what the Madden-Julian Oscillation was doing about three weeks ahead of severe weather on the Great Plains and southeastern U.S. during the typical tornado and hail months of March through June.

The goal was not to pinpoint and predict an individual event but rather forecast the expected environmental conditions that can lead to the formation of severe thunderstorms, Baggett said. That includes atmospheric instability and rotational vertical wind shear which can result in tornado and hail events.

"I would call these forecasts of opportunity," he said. "What we're trying to predict is activity, above normal or below normal tornadic or hail activity."

The team found they could predict severe weather activity on the Great Plains and southeastern U.S. about 60 to 70 percent of the time. The next step would be to partner with national operational centers like the Climate Prediction Center or the Storm Prediction Center to see if actual tornadoes and hail could be predicted in the future, said Baggett.

Hailstorms have caused more than $3 billion in insured damage in Colorado in the last 10 years. Advance warnings could potentially allow people and financial companies more time to protect cars, property and agriculture from storm damage.

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