The first major atmospheric river we’ve seen this season across the South Coast and Vancouver Island is unfolding, and it’s going to be a doozy.
Potential impacts from it could be significant, including road washouts, rockfalls, and even landslides where the heavier rain falls, along with travel delays and power outages from blustery wind gusts.
SEE ALSO: Hurricane Helene vs. B.C.’s 2021 atmospheric river—comparing devastating floods
As a result of the forecast of a Category 4-rated event, significant wind and rainfall warnings, as well as flood watches, have been issued to alert residents of prolonged heavy precipitation and strong winds through the weekend.
While 50-75 mm of rainfall is expected, up to 200 mm is possible along the North Shore of the Lower Mainland. Localized totals of as much as 200+ mm are even on the table along western and inland portions of Vancouver Island.
Winds ease compared to Friday evening, but strong, southeasterly winds up to 70 km/h will also impact areas of Vancouver Island, the Sunshine Coast and Metro Vancouver on Saturday, which could result in power outages and travel impacts, including ferries.
Wet and windy conditions persisting through the weekend
Moisture from a low-pressure system will be funnelled between a trough off the coast of B.C. and a ridge of high pressure across Oregon and California. A temperature clash will create favourable dynamics to draw up tropical moisture and steer it toward the South Coast.
The ridge to the south won’t allow the atmospheric river to slump south quickly, increasing rainfall totals across western Vancouver Island and the higher terrain across the Lower Mainland.
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Rainfall warnings are in effect for western Vancouver Island as the precipitation picks up across the region.
The rain will continue through Saturday afternoon across Vancouver Island, where up to 150 mm may fall along the coast. The mountains could see as much as 250 mm of rain from this event.
Eastern Vancouver Island is slightly protected by the rain-shadow effect, but we could still see 50-100 mm in places like Nanaimo and Campbell River. Meanwhile, Victoria is forecast to see 30-50 mm of rain, which could make for the most rain we’ve seen in one dose here since last February.
The Lower Mainland will see persistent rain through Sunday, with some heavier periods overnight Friday and into Saturday, especially for Squamish, and North and West Vancouver.
Rainfall amounts will vary greatly, from as little as 50 mm in Delta to upwards of 125 mm in downtown Vancouver. Forecasters expect general totals of 100-150 mm in the Fraser Valley, including Abbotsford, and over 100-200 mm in North and West Vancouver.
Expect ponding on low-lying roads. Landslides could become a concern in areas like Highway 4 on Vancouver Island.
The winds will also be noticeable in the south, with gusts between 50-70 km/h expected on Saturday. This could impact travel, as well, and could result in localized power outages.
For some locations in the Lower Mainland and southern Vancouver Island, this atmospheric river will be bringing some of the heaviest rainfall accumulations since the November 2021 event, which shattered rainfall records over 48 hours and cut off vital transportation routes.
Comparisons to the 2021 atmospheric river
With the expected strength of this weekend’s atmospheric river, one may wonder if any similarities can be made to the devastating and deadly November 2021 event.
Comparisons can help forecast the location of the highest impacts. 2021 November model guidance amounts vs the same model forecast this weekend.
There are many differences, including a lack of snowpack, but snowpack can act like a sponge and cause snow runoff on higher terrain. pic.twitter.com/JoUzJhBHAa
— Tyler Hamilton (@50ShadesofVan) October 19, 2024
The above post on X from Tyler Hamilton, a meteorologist at The Weather Network, shows 2021 November model guidance amounts versus the current model forecast for this weekend.
There are many differences, he said, including a lack of snowpack, but snowpack can act like a sponge and limit runoff on higher terrain.
Also, 2021 had such widespread rainfall totals of 200+ mm. with those extending values well into the Fraser Valley and the Interior, Hamilton added. That won’t be the case this weekend as the highest impacts will be much more regionalized to the North Shore and southwestern Vancouver Island.
Thumbnail courtesy of Getty Images.
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