‘Localized flooding is likely’: Atmospheric river prompts warnings in Fraser Valley

A sign warns of flooding on a stretch of Highway 7 in Maple Ridge, B.C., in this file photo. (CTV News)

Authorities issued rain and flood advisories across a wide swath of B.C.’s South Coast on Tuesday as an atmospheric river approached the region.

Environment and Climate Change Canada issued yellow rainfall warnings in Metro Vancouver, the Sunshine Coast and the west coast of Vancouver Island, as well as orange warnings for the central and eastern portions of the Fraser Valley, including Chilliwack, Hope and points east into the Skagit Valley and E.C. Manning Provincial Park.

Under ECCC’s new colour-coded warning system, yellow warnings are the most common and least severe, with moderate, localized or short-term impacts resulting from the severe weather.

Orange warnings are a step up, indicating that “severe weather is likely to cause significant damage, disruption or health impacts,” which are “major, widespread and/or may last a few days.”

For the regions under an orange warning, ECCC says rainfall amounts of 80 to 110 millimetres are possible and “localized flooding is likely.”

“Warm air with the system will cause freezing levels to rise, and snowmelt combined with the already saturated ground and heavy rain will likely result in high streamflows and localized flooding,” the orange warning reads.

“Some roads may become impassable. Visibility will likely be suddenly reduced at times.”

The weather agency also advises against driving through flooded roadways and urges people to stay away from rivers, creeks and culverts.

Meanwhile, the B.C. River Forecast Centre issued a “flood watch” Tuesday covering much of the same area as ECCC’s warning.

Flood watches are issued when “river levels are rising and will approach or may exceed bankfull,” and “flooding of areas adjacent to affected rivers may occur,” according to the river forecast centre.

Tuesday’s flood watch applies to Lower Fraser River tributaries, including the Chilliwack, Skagit, Coquihalla and Sumas rivers.

The Sumas River is also facing the potential of spillover from the Nooksack River in Washington state, where higher rainfall totals are expected in the coming storm.

“Current modelling from the Northwest River Forecast Center (NOAA) is indicating a 13 per cent chance of flows exceeding 148 feet at the Nooksack River at North Cedarville gauge,” the river forecast centre’s statement warns.

“Flows at this level could lead to spill of floodwater from the Nooksack River near Everson into the Sumas River drainage.”

It was flooding from the Nooksack River—along with an extraordinary amount of rain and breaches to the Sumas River dike system—that caused the catastrophic November 2021 flooding in Abbotsford’s low-lying Sumas Prairie area.

• Read more: Frustration over Nooksack River flooding on both sides of border

“Heavy rain and high streamflow bring increased risk for unstable banks, river erosion, submerged roads, swift water hazards, flooding and landslides,” the river forecast centre said.

“Stay clear of the banks of swift running rivers and never drive across flooded roads, bridges or river crossings. At this time of year, leaves can clog storm drains and impact urban drainage. Keep storm drains clear.”