The B.C. River Forecast Centre, which monitors snowpack across the province, says there is an ‘elevated’ risk of spring flooding due to above-average snowpacks across B.C.
In its April snow survey and water supply bulletin, the forecast centre said the average of all snow measurements across B.C. is at 12 per cent above normal.
“By early April, approximately 95 per cent of the annual B.C. snowpack has typically accumulated,” the bulletin said.
“The risk of spring flooding is elevated due to the above-normal snowpack across the entire province.”
However, the forecast centre noted snowpack levels are only one risk factor for freshet flooding.
Snowpack alone cannot predict whether flooding will occur or not.
Spring weather is also a critical flood risk factor, where the timing and severity of temperature and rainfall patterns are important drivers of flooding irrespective of snowpack levels, the forecast centre said.
The report said a major change in weather is forecast this week in which a high-pressure ridge will likely result in “very warm” temperatures in B.C.
“Since mid-March, temperatures have remained seasonable to slightly below normal through province, resulting in a slight delay in snow melt,” the bulletin said.
“An upcoming warm spell beginning the week of April 12th will kick start snow melt at low and mid elevations throughout the province. The warm weather may create challenges for smaller creeks and lower elevation areas; however, the upcoming warm weather may be considered a positive for larger, higher elevation watersheds.”
The bulletin flagged the Upper Fraser West, Central Coast, Stikine and Northwest snowpacks as “well above” normal, which is considered 25 per cent above normal or higher.
Above normal snowpack is present in the Upper Fraser East, Nechako, Lower Fraser, Similkameen, South Coast, Vancouver Island, Skagit, Peace, Skeena-Nass and Liard.
Regions with normal to slightly above normal snowpack include the Middle Fraser, North Thompson, South Thompson, Upper Columbia, West Kootenay, Okanagan, Nicola and Boundary.
“Warmer temperatures beginning the week of April 12 are expected to initiate the freshet season with low elevation snow melt and corresponding rises in streamflow, particularly in smaller creeks and low elevation areas,” the forecast centre said.
The forecast centre added the spring freshet poses a seasonal risk across the B.C. Interior.
“Scenarios that could exacerbate flood risk this year include prolonged cool weather followed by a rapid shift to persistently hot weather (particularly in May), or persistent wet weather or extreme short-term rainfall. Favourable scenarios would include continued dry weather and seasonal temperatures,” it said.