A low-pressure system in the Northern U.S. is expected to bring significant rainfall to southern Alberta, with heavy rain expected for Kananaskis, Canmore, Exshaw and Ghost Lake areas, according to Environment Canada.
Calgary could see five to 10 mm of rain, with possible thunderstorms, through to Wednesday.
Rainfall warnings were also issued for the Bow and Elbow Rivers, with the latter expected to receive 30 mm of rain on Monday, and 15 mm on Tuesday.
Forecasters are predicting 50 to 70 mm of rain for the Bow River basin and 100 to 125 mm between the Oldman River basin and Cypress Hills.
Foothill and mountain areas upstream of the vulnerable community of High River received up to 20 mm of rain over the weekend, enough to saturate the ground and produce a rapid runoff.
As a result, the Highwood River and its tributaries, already swollen by spring melt, rose another 10 cm on Saturday.
With the prospect of intense rain of up to 70 mm tonight, forecasters are worried the river may flood low-lying areas in the southern Alberta town.
Forecasters said Monday that the Highwood River could reach flood thresholds at Wallaceville, which sits along the river near Centre Street, based on current rainfall scenarios. No other area of High River is expected to see flooding.
After last year’s deluge, the town offered buyout packages for Wallaceville residents and intend to return the riverside area a natural state.
To date, 65 of 107 homeowners in Wallaceville that qualify have accepted buyout offers, according to Alberta Infrastructure.
The city of Calgary also issued an advisory Monday, saying rains are expected to increase flow rates into the Glenmore Reservior between 120 and 170 cubic metres per second (cm/s) by noon Tuesday.
The Elbow River typically flows into the reservoir at 30 cm/s at this time of year. During last year’s flood, the river peaked at 1,200 cm/s.
Calgary’s water services department has begun lowering water levels in the Glenmore Reservior in anticipation of the incoming water.
As a result, flow rates in the Elbow River could increase to 80 cm/s, still well below last year’s peak of 700 cm/s.
“We are not particularly concerned, but we have to be prudent,” said mayor Naheed Nenshi.
Nenshi said higher water levels may cause pooling on low-lying paths along the Elbow River, and the fire department will likely issue a boating advisory.
“That said, it’s an abundance of caution. At this point, there’s nothing to worry about.”
More to come ...
With files from Matt McClure and Jason Markusoff.