DAYTON, Ohio (AP) — The National Weather Service says one of the tornadoes that tore through western Ohio this week was the strongest in the state since 2010.

Survey teams have confirmed at least 18 tornadoes touched down in the region during storms Memorial Day evening and early Tuesday.

The Weather Service on Thursday upgraded one of three reported EF3 “severe” tornadoes to an EF4 , which signifies “devastating.” The service says the tornado that hit Brookville and swept through western Dayton had 170 mph winds.

The state’s last EF4 was in northwest Ohio’s Wood and Ottawa counties.

Thousands of people in the Dayton area remained without power Friday. Authorities are seeking volunteers to help with clean-up efforts.

An 82-year-old man in Celina (suh-LEYE’-nuh) was killed during the storms. More than 100 people were injured.