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May 31: Notorious Weather Day in Western Pa.

May 30, 2010

By WeatherBug Meteorologists, Patrick O'Hara and Chad Merrill

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Although May is winding down and summer vacation kicks off with the Memorial Day holiday, severe weather season is also kicking into high gear across the Mid-Atlantic and East. One date stands out like a sore thumb, though: May 31 in western Pennsylvania. Floods, tornadoes and extreme storms have all left their own indelible mark.

The biggest event in western Pennsylvania weather history occurred on May 31, 1889. The worst dam failure in American history combined with very heavy rain to produce the deadliest flood disaster in U.S. history, the Johnstown flood. More than 6 inches of rain in less than 24 hours on May 31, 1889, caused the South Fork Dam, which held back all the water from Lake Conemaugh, several miles north of Johnstown, to give way.

As much as 20 million tons of water, or the equivalent of 7,260 Olympic-sized pools, crashed down from the dam atop the Laurel Highlands through the narrow valley into Johnstown. In total, 2,200 people died, making this weather event the greatest single-day civilian loss of life in the U.S. before September 11, 2001.

On the same day almost a century later in 1985, a low pressure moving through eastern Ohio and western Pennsylvania caused a super-outbreak of tornadoes. These storms ravaged the region creating a wide path of death and destruction.

Severe storms bubbled in northern Ohio and bolted into western Pennsylvania. A total of 41 tornadoes cut a path along the I-80 corridor south of Lake Erie.

The strongest tornado formed in eastern Portage County, Ohio, approximately 6:30 p.m. EST and began its trek across southern Trumbull County, Ohio, strengthening into a top of the scale F-5 as it approached the Pennsylvania border. By the time it reached the border, the tornado was about a half-mile wide, with winds estimated near 300 mph.

The storm destroyed the cities of Newton and Niles, Ohio, as well as Wheatland, Pa. The tornado tracked just to the south of Sharon and Hermitage, Pa., and finally just to the west of Mercer, Pa., 47 miles from where it began. This was the only F-5 tornado to have formed in 1985, and remains the only F-5 tornado in recorded Pennsylvania history. Eighteen people lost their lives from this tornado, while 310 were injured.

May 31 continued to be a day of destructive weather in western Pennsylvania into the 21 st century. The greater Pittsburgh area was hit by one particularly devastating storm on that date in 2002, later named the "Kennywood Macroburst."

The storm cut a 10-mile path of destruction, mainly from straight-line winds estimated as high as 105 mph. The most concentrated area of damage was at Kennywood Amusement Park near West Mifflin, Pa.

As this storm devastated the park, a large wood pavilion which housed the "Whip" ride collapsed, killing one person and injuring 47 others. This storm was also responsible for significant power losses across the Pittsburgh region, including almost 100,000 outages across eastern Allegheny County and Westmoreland County.

Whether flooding rain, violent tornadoes or severe thunderstorms, late May will always be noted for its wild weather in western Pennsylvania.

Be sure to keep WeatherBug active to receive the latest weather in your neighborhood and get the latest updates anywhere on Twitter at WeatherBug WeatherBuzz.

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Photo Credit: The pavilion that houses the "Whip" ride collapses at Kennywood Amusement Park, near Pittsburgh on May 31, 2002. Courtesy of National Weather Service - Pittsburgh Office

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