By Laura Keil
The BC River Forecast Centre is warning that an “Extremely high snowpack” in the North Thompson and Upper Fraser East (Robson Valley) after a cooler spring could lead to rapid melt and flooding this month.
The Centre says the greatest risk for potential major flooding is if a prolonged heat event occurs in June.
Province-wide, the May 15th snowpack is the highest the province has experienced since 2012, and the Forecast Centre says there is significant seasonal flood risk in many regions.
Heavy rain or hot temperatures could trigger a rapid melt that could swell rivers and even cause instability in mountain slopes.
BC’s snowpack grew significantly between May 1st and 15th due to colder than normal spring weather, additional snow and a delay in melting for high elevation snowpacks.
The North Thompson area sat at 142 per cent of normal as of May 15th while the Robson Valley (Upper Fraser East) sat at 137 per cent of normal—possibly as high as 153 per cent of normal, if manual calculations are taken into account.
In comparison to 2012, the Centre says this year has more snow concentrated into the key tributaries of the Fraser River.
“Most notably, the headwaters of the Fraser River have well above normal snow pack (Upper Fraser East: 137%, Quesnel: 149%, North Thompson: 142%) and highlight the risk for potentially high flows throughout the watershed.”
The Centre notes that snowpack is only one factor related to freshet flood risk.
“Weather conditions from May through July will determine the timing, magnitude, and rate of snowmelt, where heavy rainfall events can exacerbate snowmelt-driven flows. An extreme heat wave—like the Heat Dome in late June 2021—could lead to significant provincial flooding if it occurred between late-May to mid-June.”
Data from 22 manual snow courses and 88 automated snow weather stations around the province (collected by the Ministry of Environment and Climate Change Strategy’s Snow Survey Program, BC Hydro and partners), and climate data from Environment and Climate Change Canada and the provincial Climate Related Monitoring Program were used to form the basis of the calculations. Future snow bulletins are scheduled for June 8th and June 17th.