State College

Pennsylvania’s tornado count is already well above average. PSU meteorologist explains why

On Friday afternoon, National Weather Service in State College meteorologists were traveling to do yet another storm survey — this one in Fulton County — to assess damage and determine whether a tornado touched ground.

These storm surveys, tornado watches and warnings and regular TV programming interruptions for storm updates from local meteorologists have felt almost routine over the past week in Pennsylvania. As severe thunderstorms brought tornadoes — including an EF4 twister with winds of up to 140 mph in Dayton, Ohio, on Monday and another EF-4 with winds of up to 170 mph in Linwood, Kansas, Tuesday — and flooding to the central United States, Pennsylvania was not left out.

Most of the state was under two back-to-back tornado watches this week — on Tuesday and Wednesday. Over those two days, at least five tornadoes were confirmed in Pennsylvania. The most recently confirmed were two EF-1 tornadoes, one in Losh Run, Perry County, with winds speeds up to 105 mph and one in Matamoras, Dauphin County, with winds up to 100 mph.

Those two tornadoes bring Pennsylvania’s count up to 27 so far this year — and counting, according to statistics given by NWS meteorologist David Martin at about 3 p.m. Friday. According to the NWS, a 28th confirmed tornado will make 2019 Pennsylvania’s sixth-highest year for tornadoes since 1950 — and the year isn’t even halfway over.

Tornado data, however, can be tricky to record, Penn State meteorology professor Paul Markowski explained. The reports tally frequently changes due to some tornadoes being double counted and others not being discovered until later, he said.

Even if the exact number might vary, the pattern is clear — this May has been abnormally high for tornadoes in Pennsylvania and across the country.

In the U.S., there have been 516 tornado reports this month, bringing the national total to 1,017, Markowski said. On average, the U.S. has 771 tornadoes by May 31. Most of those tornadoes came in a 13-day stretch, ending Thursday, during which AccuWeather says meteorologists were logging at least eight tornado reports per day across the U.S.

“It’s worth pointing out that the weather pattern can change quickly,” Markowski said. “Just two weeks ago, the tornado count was running a little below average, owing to largely unfavorable weather patterns earlier this year.”

At at least 27, Pennsylvania is also well above its 10-year average of 12 and 20-year average of 16. Reported tornado frequency has actually dropped over the past decade, relative to the preceding 20 years, Markowski explained. And most of those tornadoes have come in the past two weeks.

Erin Grubb looks though a neighbor’s home on Kline Road in Denver, Pa., Monday, May 20, 2019. The roof was completely blown off the house in a storm that moved though the area at about 8:00 Sunday evening. (Blaine Shahan/LNP Media Group via AP) (Blaine Shahan/LNP Media Group via AP) Blaine Shahan AP

Although on average, most tornadoes over the past 20 years in Pennsylvania occurred in July, Markowski said they can occur at any time of year or hour of the day, so long as the conditions present themselves.

As for what causes a tornado, Markowski says it’s warmth and humidity in the lower atmosphere, relatively cold air overhead, and considerable variation of wind speed and/or direction — known as wind shear.

What made the past week unique, he said, is that that pattern never let up.

“It’s rare to have three or four days in a row in the same general area, at least in this part of the country, in which conditions favor tornadoes,” he said.

As for whether this uptick in tornadoes has to do with climate change, Markowski pointed to an article he, along with fellow Penn State meteorology professor Yvette Richardson, penned for the Washington Post in 2017. Although most climate models do predict that there will be more days per year when the atmosphere will have sufficient instability and wind shear to support tornadoes, that doesn’t necessarily mean there will be more tornadoes, they wrote. There are other factors that affect whether a tornado forms, and climate models don’t capture tornadoes.

In addition to the tornadoes, Pennsylvania also dealt with severe thunderstorms, hail and flash-flooding over the past week. The 500 block of North Centre Street in Philipsburg, in front of Weis Markets, was briefly shut down Thursday due to flooding.

According to NWS online statistics, 6.22 inches of precipitation have been recorded in State College this May. That’s the fourth-highest month for precipitation since the start of 2018 — the wettest year on record for the area. Penn State’s Weather World recorded 21 days with measurable precipitation in Harrisburg this month.

However, there is good news on the horizon. Markowski says that that seemingly unending weather pattern has finally changed, the humidity has dissipated and with it the risk of thunderstorms.

“The risk of storms will return over the weekend, but there won’t be as much wind shear in the atmosphere,” he said. “Thus, tornadoes won’t be much of a threat in the next couple of days, fortunately. “