Deep snowpacks in the North and South Thompson basins means the flood risk this spring is greater than it was in 2019.
The Feb. 1 snow survey from the River Forecast Centre includes data from 101 manual snow courses and 81 automated snow weather stations around the province. Snow levels range from a low of 87 per cent of normal in Skeena-Nass to a high of 134 per cent of normal in Skagit.
The South Thompson basin’s snowpack is second-greatest in the province, relative to normal amounts, at 130 per cent. North Thompson is at 119 per cent of normal. Provincewide, the snowpack is 110 per cent of normal, a significant increase from the 84 per cent mark measured on Jan. 1.
A year ago, the snowpack was much thinner, provincially at 97 per cent of normal and at 112 per cent of normal in the North Thompson and 87 per cent of normal in the South Thompson.
The River Forecast Centre said seasonal flood risk conditions are developing in many areas, including the South Thompson, noting the final one-third of snow accumulation typically occurs in February, March and April.
“While changes to the overall provincial seasonal flood risk are possible over the next few months (either increases or decreases), current trends in snowpack are likely to persist,” the centre stated in its February snow survey and water supply bulletin, with data being taken on Feb. 1.
January’s constant storms and what meteorologists call “sub-tropical atmospheric rivers” built up the snowpack.
“For snow-melt dominated rivers in the interior of the province, the likelihood of spring flooding increases with high snowpacks,” the centre said. “This is most pronounced when snow basin index values approach or exceed 120 per cent. This does not mean that spring flooding will occur; rather, the chances of flooding are increased.”
The centre said precipitation was persistent throughout most of January for most areas of the province, in particular within the South Coast, Vancouver Island and South Interior. Most Environment and Climate Change Canada weather stations reported wet conditions, with precipitation in the 120 per cent to 200 per cent of normal range.
On the ski hill, Sun Peaks Resort was reporting as of Feb. 9 an alpine snow base of 218 centimetres and a mid-mountain snow base of 198 centimetres. Those measurements were 157cm/117cm in 2019 and 216cm/167cm in 2018.
The Climate Prediction Center at the U.S. National Weather Service is forecasting a high likelihood of of continued neutral El Niño Southern Oscillation conditions into the spring and continuing through the summer, with neutral conditions usually having a less predictable association with snowpack conditions in B.C. compared to El Niño and La Niña conditions.
Looking ahead, Environment Canada is predicting cooler than normal temperatures for February through April for most of British Columbia, while normal to above-normal snow accumulation is expected through the next three months.
Flood risk is further amplified by sudden heat waves and heavy rain in the spring.