The tornadoes and thunderstorms that battered areas of New York State, Pennsylvania, Ohio, West Virginia and Canada were caused by two atmospheric conditions, weather analysts say.
Officials said the weather pattern began with a ``strong`` cold front that had been moving across the nation for several days. The front, associated with a low-pressure center, moved eastward across the Great Lakes through the Ohio River Valley and into western New York State Friday afternoon, said Ed Ferguson, deputy director of the National Weather Service`s Severe Storms Forecast Center in Kansas City, Mo.
The cold, drier air of this front plowed into a mass of warmer wet air, forcing it to rise into the atmosphere and condense into clouds that produced ``very violent`` thunderstorms, Ferguson said.
At the same time, two jet streams above the storm, at an altitude of 30,000 feet, swept over the cloud ceiling at a velocity of 125 mph, he said. This created a continual ``vertical lift of extreme intensity`` by which air is sucked upward. It is this upward draft of moist air that spawned the funnel-shaped clouds of violent, swirling 200-mph winds.
In the areas they struck, the tornadoes followed a heavy deluge of rain and hail.
``We are in the peak of the tornado season`` of April, May and June, Ferguson said, ``but this was a very violent storm. This storm could go on record as one of the worst outbreaks.``
He said the Forecast Center issued three tornado watches to local weather bureaus, airlines and news media outlets Friday afternoon and evening. The first was issued to the areas of eastern Ohio, northwest Pennsylvania and western New York State at 4:25 p.m., about 40 minutes before the first tornado touched ground in Erie, Pa.
The service issued the second watch at 7:22 p.m., for north-central Pennsylvania and north-central New York. Ferguson said the third went out to areas of central Ohio and Pennsylvania, parts of northwest West Virginia, southwest New York and northeast Kentucky, at 8:14.