A powerful atmospheric river is delivering another prolonged stretch of heavy rain to B.C.’s South Coast, with new yellow and orange rainfall warnings in effect Wednesday. Environment and Climate Change Canada says the storm will bring a range of impacts across Metro Vancouver and the Fraser Valley, where rain is expected to intensify in the afternoon and early evening before tapering off Wednesday night. Yellow rainfall warnings are now in effect for Vancouver, Burnaby, Surrey, Langley, Coquitlam, Maple Ridge, the North Shore, Howe Sound, the Sunshine Coast and the southern Sea-to-Sky Highway. Those areas are forecast to receive 40 to 70 millimetres of rain through the evening. The western Fraser Valley, including Abbotsford, is also under a yellow warning with 60 to 90 millimetres expected. Farther east, Environment Canada has issued orange rainfall warnings for Chilliwack, Hope and Highway 3 from Hope to Princeton, where 80 to 110 millimetres of rain are possible and localized flooding is likely. A ‘storm highway’ aimed directly at the South Coast Meteorologist Ken Dosanjh with Environment and Climate Change Canada says two high-pressure systems on either side of the province are steering moisture into B.C. “Think of those almost as like the bread of a sandwich,” Dosanjh said. “We’ve created essentially a storm highway where all these Pacific weather systems are able to just pretty much direct themselves all the way to our region.” Dosanjh says this system is the second part of a two-stage event, with Monday’s rainfall laying the groundwork for more significant impacts Wednesday. “Monday’s system went through, it kind of pre-saturated a lot of the soils. And so now for this second part… precipitation intensity is a little bit higher,” he said. Rainfall intensifying by the hour Many areas had seen 20 to 30 millimetres of rain by mid-morning, but Dosanjh cautions the heaviest precipitation is arriving later in the day, with forecasters expecting “rates to rise successively with each hour,” before peaking in the late afternoon or early evening. “We’ve already saturated the soils quite a bit, and now we’re only going to start to increase the intensity of rainfall.” With soils unable to absorb much more water, he says there is concern about an increased risk of landslides. North Shore, Chilliwack and Hope among the hardest hit areas Within Metro Vancouver, the North Shore is expected to receive the highest rainfall totals. “Those areas can expect to get a little bit more intensity throughout the day today,” Dosanjh said. “We’re looking, on average, (at) an additional 30 to 40 millimeters for today.” The intensity increases farther east. “As you continue to progress eastwards through the Fraser Valley… Chilliwack, Hope and Highway 3 through Allison Pass, we’ve increased our alert color level to orange,” he said, noting these areas could see 80 to 110 millimetres of rain. He added that the eastern Fraser Valley is closer to the core of the atmospheric river as it hits the Cascades, which contributes to higher rainfall totals. Rising freezing levels add to flood concerns Warm, moist air is pushing freezing levels to between 2,000 and 2,500 metres. That creates conditions for snowmelt, especially in shallower early-season snowpacks. “It can melt that as it’s not stable and strong enough, and so that can also produce rain on snow and additional stream flow runoff,” Dosanjh said. “On top of the amount that we’re currently expecting, you can expect a little bit more enhancement due to the snow melt.” Flooded roadways and fast-moving water remain major concerns across the region. “We are concerned with flooded roadways, as well as being cautious near rivers, creeks and culverts,” he said. Environment Canada continues to warn the public: Don’t drive through flooded roadways. Avalanche risk climbing as rain falls on recent snowfall With recent snowfall at higher elevations, warmer temperatures and rain are contributing to unstable conditions. “Rain on snow melt is also an additional factor, and that can also include avalanche risk as well,” Dosanjh said, adding that Avalanche Canada is monitoring the situation closely. How the colour-coded warning system works The province’s updated alert system uses yellow, orange and red warnings to communicate degrees of risk. Dosanjh says this helps the public better understand how weather impacts different regions. “The colors basically tell you what the risk is to you,” he said. “The weather alert color moves from yellow to orange to red as the potential risk increases.” He notes that the same type of weather can have different effects depending on a region’s terrain, soil conditions and population. In this case, he says the eastern Fraser Valley is seeing “heightened sensitivities” due to saturated ground and heavier precipitation. Active weather pattern expected to continue Looking ahead, Dosanjh says British Columbians should be prepared for more unsettled weather. “We are looking at a pretty active weather pattern and season for the coast,” he said. “Conditions can change quickly… the best way to stay prepared is to keep up to date on our latest forecasts and weather alerts.” He added that it is too soon to predict whether the South Coast could see a White Christmas.
