About 50 to 70 millimetres of rain is expected to fall in the Ottawa region from Wednesday to Thursday afternoon, Environment Canada said in a weather warning issued Tuesday.
"Higher amounts are possible in thunderstorms," Environment Canada said. "Heavy downpours can cause flash floods and water pooling on roads."
Showers are expected to start Wednesday afternoon with the risk of a thunderstorm, and about 10 to 15 mm of rain could fall.
The rain is expected to continue Wednesday night — about 20 to 30 mm — with another risk of a thunderstorm. Showers or thunderstorms are also expected on Thursday.
So far, the forecast for Friday calls for a 60-per-cent chance of showers or thunderstorms.