Parts of B.C. at risk of dangerous floods due to unseasonably cold spring

Delayed snowmelt in parts of British Columbia due to unseasonably cold temperatures has raised the potential for a dangerous late flood season, according to an official with the B.C. River Forecast Centre. 

The centre's latest snowpack bulletin is reporting significant accumulation in parts of the province already dealing with record snow depth and says a colder-than-normal April and start of May has delayed melting.

Provincial data shows the snowpack, which is the seasonal accumulation of slow-melting packed snow, increased by 15 per cent between April 1 and May 1.

Hydrologist Jonathan Boyd with the B.C. River Forecast Centre says there is cause for concern if temperatures rise substantially later this month.

He compares current conditions to historic spring flood seasons the province experienced in 1948 and 1894. 

He says the worst spring floods that B.C. has had in the past 130 years have been related to cold temperatures in April and early May, followed by extreme heat and relatively hot weather.

"The concern is that this year has been very similar and it's just a matter of if a big, high-pressure ridge type of event settles over the province," he said. "There is the risk for fairly significant flooding provincewide if that were to happen."

He says the catastrophic November floods have made many of the province's rivers vulnerable to freshet high flows.

 A sudden temperature shift of 6 C or 7 C above normal would be enough to cause concern, Boyd said, but there is potential for bigger temperature swings given the recent chilly weather. 

"If we end up with extreme heat followed by heavy, warm rain, it's really the worst case scenario," Boyd said.

Boyd says forecasters typically have a two-week window to predict any worrisome weather but flood watches and warnings can come suddenly due to local conditions. 

The forecast centre says it will continue to monitor snowpack conditions and will provide an updated seasonal flood risk forecast in the May 15 bulletin, which is slated for release on May 20.