BUFFALO, N.Y. (AP) — More than 13,000 people have lost power after severe storms ripped through western New York, uprooting trees and knocking down power lines.

Erie County Executive Mark Poloncarz advised no unnecessary travel after strong thunderstorms moved through towns south of Buffalo Thursday afternoon. He said there was “possible tornadic activity.”

National Grid reported about 400 customers without power in the Buffalo area and NYSEG reported more than 13,000 out.

The National Weather Service issued a tornado warning early Thursday afternoon and said it’s investigating whether the storm damage was caused by a tornado or straight-line winds.