A flood watch is in effect for the North Shore and a wide swath of coastal British Columbia as a prolonged atmospheric river continues to dump heavy rain on a region where rivers are already swollen.
The River Forecast Centre upgraded the watch on Wednesday to cover the North Shore Mountains and Metro Vancouver tributaries, Howe Sound, the Sea-to-Sky Corridor, the Sunshine Coast, and lower Fraser tributaries including the Fraser Valley.
The storm has already delivered 100 to 120 mm of rain at lower elevations and 150 to 170 mm at higher elevations over the past four days. An additional 50 to 150 mm or more is expected across the South Coast through Friday, with precipitation rates forecast to intensify on Wednesday evening.
Freezing levels are expected to hold between 2,000 and 2,500 metres — possibly reaching 3,000 metres in some areas — throughout the storm. That means the snowpack deposited during the storm’s earlier phase is at significant risk of rapid melting, with melt rates potentially reaching 30 to 50 mm of snow-water equivalent per day across multiple elevation bands. Rain falling directly onto fresh, vulnerable snow is expected to substantially amplify runoff.
Many rivers across the South Coast were already at or near an initial peak as of Wednesday afternoon, the forecast centre said. Further rapid rises are expected as the storm’s next band moves in. Because river levels are already elevated and the ground is fully saturated, the hydrological response to additional rainfall is likely to be faster and more extreme than under normal conditions.
River peaks are expected to arrive on Thursday and could persist through Saturday. The forecast centre is projecting peak flows reaching two to five-year return periods across many river systems, with some receiving the heaviest runoff potentially reaching 10 to 20-year return periods or higher, a threshold that indicates significant and unusual flood magnitude.
Residents are urged to stay away from riverbanks and to avoid driving through floodwater or across road washouts. Current road conditions are available at DriveBC.ca.
