On the evening of May 31st, 1985, a devastating and deadly tornado outbreak struck the Northeastern United States and Canada. 43 tornadoes and numerous damaging thunderstorms tore across Ohio, Pennsylvania, New York, and Ontario. This event was the deadliest tornado outbreak of the 1980’s; killing 89 people in total, injuring more than 1,000 others, and racking up more than $600 million in property damage. In fact, since May 31, 1985, only two tornado days have been deadlier in the entire United States.
The storms were the result of high levels of atmospheric instability present in an environment favorable for tornadic thunderstorms, triggered by the passage of a strong late-spring cold front. Quoting the original survey report produced by NOAA in 1985, “perhaps the lesson to be learned from the 1985 outbreak is that under the proper atmospheric conditions, major tornadoes can occur irrespective of the location or terrain”.
The visible satellite loop above shows the development and explosive growth of thunderstorms across southern Ontario, Ohio, western Pennsylvania and western New York on the afternoon of May 31st.
The thunderstorms were supported by a cold front moving east across the northeastern U.S. ahead of a low pressure system moving northeastward through the Great Lakes region. Unseasonably warm and humid air moved northward into Pennsylvania and much of the eastern U.S. ahead of the cold front, setting the stage for strong thunderstorms and tornadoes.
The three ingredients needed for thunderstorms are lift, moisture and instability. The cold front moving east provided the lift as it pushed into the warm sector and the dewpoints into the 70s show the available moisture. The combination of moisture, instability, lift, and wind shear were present across a large area of the northeastern U.S. on May 31st. What happened next is history…historical damage and destruction.
Source: National Weather Service