Graph from B.C.’s River Forecast Centre shows how much snow had accumulated in the North Thompson River watershed as of March 1 for the past several years. (River Forecast Centre graphic)

Graph from B.C.’s River Forecast Centre shows how much snow had accumulated in the North Thompson River watershed as of March 1 for the past several years. (River Forecast Centre graphic)

Spring freshet might be high this year

By Keith McNeill

With a snow basin index at 123 per cent of normal as of March 1, the North Thompson River has an elevated seasonal flood risk, according to B.C.’s River Forecast Centre.

The snow basin index for the South Thompson was at 127 per cent of normal.

The Skagit River basin had the highest snow basin index in the province, at 139 per cent of normal.

Other river watersheds with snow basin indices of 120 per cent or higher included Upper Fraser West, Upper Fraser East, Boundary, and Central Coast.

The snow basin index for the entire Fraser River basin (meaning upstream from the Lower Mainland) was 117 per cent.

Given that the Upper Fraser and Thompson River greatly influence the overall freshet flow on the lower Fraser River, the seasonal flood risk for the entire Fraser River was rated by the centre as “substantial.”

The River Forecast Centre points out that, while the likelihood of spring flooding increases with high snowpack, it does not necessarily mean that a spring flood will occur.

Much depends on the weather. A cool, wet spring would lead to increased risk while warm and dry weather might partially alleviate some of the risk.

Neutral El Nino Southern Oscillation (ENSO) conditions have been in place since last summer. Compared to El Nino and La Nina conditions, neutral ENSO conditions generally have a less predictable association with snowpack and weather conditions – meaning they make it hard to forecast what’s going to happen.

Snow