United States–Canada tornado outbreak: Forty-one tornadoes hit Ohio, Pennsylvania, New York, and Ontario, leaving 76 dead.

The 1985 United States–Canada tornado outbreak, referred to as the Barrie tornado outbreak in Canada, was a major tornado outbreak that occurred in Ohio, Pennsylvania, New York, and Ontario, on May 31, 1985. In all, 44 tornadoes were counted including 14 in Ontario, Canada. 90 people were killed, with 14 deaths occurring in Canada, and 76 occurring in the United States. It remains the largest and most intense tornado outbreak ever to hit this region, and the worst tornado outbreak in Pennsylvania history in terms of deaths and destruction.

Ohio is a state in the Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the west, and Michigan to the northwest. Of the 50 U.S. states, it is the 34th-largest by area. With a population of nearly 11.9 million, Ohio is the seventh-most populous and tenth-most densely populated state. Its capital and most populous city is Columbus, with other major metropolitan centers including Cleveland and Cincinnati, as well as Dayton, Akron, and Toledo. Ohio is nicknamed the "Buckeye State" after its Ohio buckeye trees, and Ohioans are also known as "Buckeyes".

Pennsylvania, officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Maryland to its south, West Virginia to its southwest, Ohio and the Ohio River to its west, Lake Erie and New York to its north, the Delaware River and New Jersey to its east, and the Canadian province of Ontario to its northwest via Lake Erie. Pennsylvania's most populous city is Philadelphia, while the capital of the state is Harrisburg. It is the fifth-most populous U.S. state, with over 13 million residents as of the 2020 United States census, as well as being the ninth-highest by population density and the 33rd-largest state by land area. The largest metropolitan statistical area is the southeastern Delaware Valley, including and surrounding Philadelphia, the state's largest and nation's sixth-most populous city. The second-largest metropolitan area, Greater Pittsburgh, is centered in and around Pittsburgh, the state's second-largest city.