Think 16 Tornadoes In A Year Seems Extreme? You’re Not Wrong — It’s Above Average For Pa.
Is extreme weather becoming more common in Pennsylvania? After the spring we’ve had, it may be hard to find someone who would disagree with that assumption.
Strong to severe thunderstorms rattled the region Thursday, with six tornado warnings issued across the state in a span of just two hours.
All six warnings expired without incident, but the outbreak of severe weather over a short period of time is notable. Especially when it seems to be part of a pattern of extreme weather events this season.
In April, a 100-yard-wide tornado that reached maximum speeds of 85 mph touched down in Scranton and Dunmore. National Weather Service officials confirmed the weak tornado after a survey of a 3-mile swath that began on Maple Street in Scranton and concluded at Sherwood Park in Dunmore.
At least 16 tornadoes have been preliminarily confirmed in the commonwealth this year, according to National Oceanic and Atmospheric Administration’s Storm Prediction Center. The state’s average for an entire year is closer to eight, according to a storms event database that goes back to 1950.
Forecaster John Homenuk of Empire Weather was on the ground earlier this week when a series of powerful tornadoes ripped through the Midwest. He suspects many people will point to a definitive link with warming global temperatures and tornadoes in places where they “should be” less common.
But Homenuk says the effects of global warming on the processes and patterns that lead to tornadoes are mostly unknown.
“What we can say for sure is that there are oscillations — well documented down periods and up periods. We are in a more active period right now, without a doubt,” Homenuk said.
John Hart, lead forecaster for the Storm Prediction Center, said there is no known trend in the data or pattern that indicates severe storms are becoming more frequent in Pennsylvania.
The state is simply stuck in an active period and typically has such patterns separated by a few quiet years.
Data from NOAA’s Annual Severe Weather Report Summary supports that explanation. It shows Pennsylvania averaging roughly 11 tornadoes from 2012-16. But in 2017 there were 26 documented tornadoes. Last year, that number jumped to 31, including one that ripped through the Arena Hub Plaza in Wilkes-Barre Twp. on June 13.
To obtain critical weather information, especially in less-populated areas, the weather service relies on a volunteer program with between 350,000 and 400,000 trained severe weather spotters who provide timely reports of severe weather.
Those reports are coupled with Doppler radar technology and satellite data to pinpoint areas where tornadoes are suspected to have touched down.
“The technology boom has led to a vastly improved network of spotters and observations, which has made tornadoes more visible. It has also massively improved warning times and communications,” Homenuk said.
In each instance where the National Weather Service suspects a tornado occurred, a storm survey team is dispatched to inspect the damage. The survey team’s mission is to gather data to reconstruct a tornado’s life cycle, including when and where it initially touched down and lifted (which determines its path length), its width and magnitude.
A survey team dispatched by the National Weather Service will conduct a full ground survey in order to assess tornado damage, but occasionally, an aerial survey is conducted if the extent of the damage is large enough.
Tornado strength is rated based on the Fujita Scale, classifying tornadoes from EF-0 to EF-5.
The Enhanced Fujita Scale is used to classify tornadoes into the following categories:
EF-0 weak: 65 to 85 mph
EF-1 weak: 86 to 110 mph
EF-2 strong: 111 to 135 mph
EF-3 strong: 136 to 165 mph
EF-4 violent: 166 to 200 mph
EF-5 violent: >200 mph