The National Weather Service has confirmed that a tornado touched down in Coudersport Thursday.
More than 2100 customers in Potter County are still without power, and Penelec hopes to have it restored Sunday evening.
In McKean County, where more than 2,400 customers are still without power, the storm was a microburst, which is characterized by straight line winds.
200 of the customers without power are in the Lewis Run area. Penelec expects to have power restored by late Sunday night.
No serious storm-related injuries have been reported in McKean County, but in Potter County 66-year-old Linda Button of Andover, New York, was killed by a falling tree at a campground in Genesee Township.
About 3,500 customers in Elk, Cameron and Forest counties are still without power as well. Penelec expects to have most power there restored by this evening.
In Chemung and Steuben counties in New York, three tornadoes touched down Thursday.
The first hit near Southwest Corning at around 3:30. The second was near South Corning at 3:45. The third hit Elmira at 4 p.m., and spread damage over 10 miles.
No serious injuries were reported.