Forecasters say some of today's thunderstorms may pack a big punch, with winds strong enough to damage trees and power lines.

Environment Canada has issued both a severe thunderstorm watch and a heat warning for the Montreal Island area, as dangerous heat and unstable weather take hold to start the week. Temperatures will soar to 32°C this afternoon,

At 1:39 p.m. on Thursday, the National Weather Service issued a severe thunderstorm watch in effect until 10 p.m. for Columbia, Lycoming, Montour, Northumberland, Snyder, Sullivan, Tioga and Union counties.