Ottawa could see 15-25 mm of rain tonight and Wednesday. Here’s when the heavy rain will begin

A rainy Tuesday morning in downtown Ottawa. (Josh Pringle/CTV News Ottawa)

Ottawa is set to receive a soaking from Mother Nature, with 15 to 25 mm of rain expected tonight and Wednesday.

Environment Canada’s forecast initially called for 10 to 20 mm of rain today, 15 to 25 mm of rain tonight and another 5 to 10 mm of rain on Wednesday.  The updated forecast at 3:30 p.m. calls for 10 to 15 mm of rain tonight and another 5 to 10 mm on Wednesday.

The record for greatest rainfall at the Ottawa International Airport on May 6 is 19.6 mm, set back in 1952. Another weather station in Ottawa recorded 22.6 mm of rain on May 6, 1989.

The forecast calls for showers to begin this evening. There is a risk of a thunderstorm this evening and overnight. Low 12 C.

Environment Canada says the rain will begin around 6 p.m.

Wednesday will see more rain. There is a risk of a thunderstorm in the morning. High 14 C.

The outlook for Thursday calls for a mix of sun and cloud with a 30 per cent chance of showers. High 13 C.

Friday will be cloudy with a high of 14 C.

The normal temperatures for this time of year are a high of 18 C and a low of 7 C.

Flood warning

A flood warning remains in effect for the Lower Ottawa River, between Arnprior and Hawkesbury.

“Water levels and flows have been steadily rising along the Ottawa River due to seasonal rainfall combined with ongoing snowmelt in the northern basin,” conservation authorities said in a statement Monday evening. “Flows and water levels are expected to stabilize over the coming days.”

Minor flood levels have been exceeded along the Ottawa River from Pembroke to Britannia, while minor flood thresholds are expected to be exceeded this week from Gatineau to Hawkesbury.

The statement says water levels may decrease later this week in the Constance Bay, Britannia and Cumberland Village areas.

“Current forecasts suggest that water levels on the main Ottawa River will remain 80 - 150 cm below the 2019 historic flood levels, and below 2023 peak levels,” officials say.

The flood warning was issued by the Mississippi Valley Conservation Authority, the Rideau Valley Conservation Authority and the South Nation Conservation.