Atmospheric river to raise flood risk across B.C. coast, river forecast centre says

The B.C. River Forecast Centre issued high streamflow advisories for the entire coast on Friday ahead of an atmospheric river that's expected to arrive Sunday. (B.C. River Forecast Centre)

The B.C. River Forecast Centre issued high streamflow advisories Friday for the entire B.C. coast, including Vancouver Island, the Lower Mainland, and coastal areas as far north as the Alaska border.

“A strong atmospheric river is forecast to impact coastal British Columbia beginning mid-day on

Sunday, and potentially continuing for several days," the statements read.

A high streamflow advisory means “river levels are rising or expected to rise rapidly,” but “no major flooding is expected,” according to the river forecast centre.

The coming storm is forecast to bring 200 millimetres of rain or more in the hardest-hit areas, such as the west coast of Vancouver Island, Howe Sound and Prince Rupert, with 100 millimetres possible in Metro Vancouver.

Freezing levels are also expected to rise to more than 3,000 metres above sea level by Monday, leading to runoff from melting snow.

“Uncertainty remains regarding the exact duration and intensity of the atmospheric river,” according to the advisories.

“Forecast models suggest the potential for multiple pulses of rainfall, which could extend the period of elevated runoff and river response through the middle of next week or longer.”

Environment and Climate Change Canada issued a special weather statement about the storm Friday afternoon, warning that “extensive water pooling on roads and wash-outs may occur,” along with “enhanced risk of landslides due to saturation of landscapes.”

The river forecast centre says it expects rivers across the coast to begin rising on Monday, reaching their peaks “early to mid-next week” depending on “the timing and intensity of the heaviest rainfall.”

“High-end scenarios indicate the potential for conditions to escalate above a high streamflow advisory, with key hazards including the potential for pooling water, overbank flow, bank erosion, washouts and landslides,” the advisories read.

The step above a high streamflow advisory in the forecast centre’s system is a flood watch, which means “river levels are rising and will approach or may exceed bankfull,” and “flooding of areas adjacent to affected rivers may occur.”