1985 United States – Canadian tornado outbreak

The 1985 United States-Canadian tornado outbreak was a major tornado outbreak that occurred in Ohio, Pennsylvania, New York, and Ontario, on May 31, 1985. Forty-three tornadoes were counted including 13 in Ontario. It is the largest and most intense tornado outbreak ever to hit this region.

The tornado outbreak was caused by a powerful low pressure system that traveled across the Midwestern United States during the early hours of May 31. A warm front associated with the storm sparked heavy thunderstorms during the pre-dawn hours. In the morning, the sun came out and temperatures soared into the mid to upper 80 degrees (high 20s to low 30s degrees C) with a high humidity level, conditions typically seen during the summer months. However, a cold front which accompanied the system set up the stage for severe weather during the late afternoon hours.
[edit] Storm timeline and aftermath

The outbreak lasted roughly from just after 4 PM EDT, when the first tornado touched down in Ontario, until 11 PM EDT when tornadoes struck central and southern Ohio. However, the peak of the outbreak took place during the early evening hours, where the deadliest tornadoes across western Pennsylvania and eastern Ohio took place.

In all, 88 people lost their lives. It was the third costliest tornado outbreak in the history of the U.S., where it caused $450 million (1985 U.S. dollars) damage in Ohio, Pennsylvania, and New York. It was also one of the costliest in Canada: damage in Ontario totalled an estimated $100 million USD. The damage would total nearly $1 billion in 2005 US dollars.

http://en.wikipedia.org/wiki/1985_United_States_%E2%80%93_Canadian_tornado_outbreak