OSWEGO - Tens of thousands of residents remained without electricity Wednesday after severe thunderstorms rolled across upstate New York a day earlier.

Tuesday's storms knocked over trees, brought down power lines and damaged homes in an area stretching from the Rochester area to the Catskills and the Vermont border.

Authorities in St. Lawrence County in northern New York issued an advisory against unnecessary travel because of extensive storm damage there.

National Grid reported about 32,400 of its customers were without power Wednesday, with the hardest hit areas in Oswego, Lewis, Franklin and St. Lawrence counties. The utility said as many as 68,000 of its customers were without power at the peak of the storm. New York State Electric & Gas reported about 9,500 without power, most of them in the Catskills, while Central Hudson Gas & Electric said it had 30,000 outages in Ulster, Dutchess and Orange counties.

Improved weather will help crews restore power to some NYSEG customers Wednesday, but others may not get their electricity back until Friday, utility spokesman Clayton Ellis said.

High winds also blew down power lines, closing a section of Interstate 81 for several hours Tuesday. In Syracuse, a section of roof was blown off Bishop Ludden High School, forcing school officials to cancel classes Wednesday so repairs could be made.