Snow pack levels in two Upper Fraser watersheds are well above normal, according to an update from the B.C. River Forecast Centre, raising concern the Central Interior could be in for a bout of flooding.
As of May 1, the level for Upper Fraser West stood at 140 per cent of normal while that for Upper Fraser East was 125 per cent, both up noticeably from 95 and 117 per cent the month before as unseasonably cool weather not only delayed snow melt but led to some late-season snowfall.
The measurements indicate a "significantly increased the risk of flooding this spring," the RFC said in the bulletin but cautioned that snow pack is only one factor in whether the Fraser and other rivers will burst their banks.
"Weather conditions from May through June determine the timing, magnitude, and rate of snow melt, 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 mid-May to mid-June," the RFC says.
Nonetheless, the RFC is forecasting runoff levels of 115 per cent at Shelley and 113 per cent at McGregor at Lower Canyon, although just 102 per cent at McBride.
The level for Upper Fraser East could be even higher, the agency noted as this was the first season that manual snow surveys at Longworth Upper and Knudsen Lake were discontinued.
If the automated stations at the spots used historic data from their predecessors, Longworth Upper would stand at 141 per cent and Knudsen Lake at 153 per cent and boost the level for the watershed to 132 per cent.
The level in Upper Fraser East could also spell trouble for the Lower Mainland as it contributes about 30 of the total flow for the Fraser River at Hope, according to the RFC. However, the area has seen higher levels, reaching 143 per cent as of the same point in 2020. Upper Fraser West, in turn, hit 264 per cent in 2018.
Measurement for the Nechako watershed was 104 per cent, up from 88 per cent as of April 1 but still within the range of 90-110 per cent the RFC considers near normal.
