A severe thunderstorm swept through much of southern Ontario Sunday evening, knocking out power to thousands of hydro customers.

At its peak, Hydro One's outage map showed nearly 40,000 customers without power as of midnight Monday.

That number fell dramatically overnight, with nearly 13-thousand customers affected by outages as of 3 a.m.

Environment Canada issued severe thunderstorm watches for a large swath of southern Ontario, stretching from Brantford to Ottawa to Cornwall and Prescott.

The statements said the thunderstorms brought torrential rain, damaging wind gusts and strong hail.

Those weather watches have since been lifted.