PITTSBURGH — A year ago, unprecedented storms swept across the region, knocking out power for half a million people.
As another severe weather season gets started, Pittsburgh’s Chief Meteorologist Stephen Cropper is looking at how those seasons are changing.
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It wasn’t your typical thunderstorm: a fast-moving, straight-line windstorm — a powerful derecho, more likely in summer, making an early-season appearance.
The intensity and impact brought with it some of the strongest winds ever to directly impact Pittsburgh, and left half a million people without power.
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A few months later, the damage from the derecho was matched by deadly flash flooding: as much as 4 inches of rain in just over an hour — a surge so fast, it swept vehicles into creeks and collapsed buildings. Nine people died, including a 3-year-old.
“I think that the science is still out, at least here for Pittsburgh, whether storms are getting stronger or not,” said Colton Milcarek, a meteorologist for the National Weather Service in Pittsburgh.
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But we do know how they’re changing. For storms to form, they need moisture, rising air or instability and something to trigger lift, such as a cold front.
Temperatures are warming up faster in spring, and that’s giving our severe weather season a jumpstart.
And historically, June has been our most active month for severe weather.
But what we’re seeing is the slightly earlier start to those seasons as we get more instability in the springtime.
Basically, that means we’re getting earlier starts to severe weather.
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And warmer air also holds more moisture. Think of a sponge like the atmosphere: it’s juiced when moisture condenses, it can fuel a storm’s damaging winds, and set them up to bring heavy downpours and increased flooding.
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“So when we have more moisture, and we have warmer temperatures, and that’s basically a two-fold favorability for storm development,” Milcarek said.
The warmer, wetter trend is expected to continue this summer, meaning the threat for more damaging winds and heavy downpours
We are a little bit more concerned about flash flooding than normal, but the water in the atmosphere is just one piece of the puzzle.
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