Atmospheric river to kick off winter storm season with a bang in British Columbia, Washington

The first potent storm of the autumn and winter season for British Columbia and part of Washington will be a doozy with enough rain to cause flash flooding and cause travel issues, AccuWeather meteorologists warn.

The first potent storm of the autumn and winter season for British Columbia and part of Washington will be a doozy. Enough rain may fall to cause flash flooding and cause travel issues.

"A plume of moisture will extend from well out over the Pacific Ocean and be directed at southern British Columbia and the northwestern corner of Washington," AccuWeather Senior Meteorologist Brett Anderson said. "It will behave like a giant firehose or atmospheric river."

The major Canadian city of Vancouver, British Columbia, will be the most adversely affected by the storm, but enough rain will fall on Seattle to thoroughly soak the metro area.

The storm will begin to affect the region on Friday and continue through the weekend, with one surge coming from Friday to Saturday and a second round on Sunday.

"Rainfall of 5-10 inches will easily fall on the west-facing slopes of Vancouver Island with a general 4-8 inches on the western slopes of the Olympics in northwestern Washington and the lower slopes of the Coastal Range in southern British Columbia," Anderson said. "Up to 14 inches of rain may pour down in the wettest spots."

The rate of rain may exceed 2 inches per hour at times, which can challenge storm drains. Where leaves have fallen, or other debris is blocking the drains, street and highway flooding will be a concern. In hilly areas, heavy rain can lead to rock and mudslides.

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Snow levels will fluctuate and will be between 3,000 and 4,000 feet at the onset of the storm on Friday, rising to 6,000 to 7,000 feet on Saturday, then falling back to 5,000 feet or so on Sunday. Where heavy snow initially falls in the higher elevations and switches to heavy rain, the flooding of streams and rivers could be rapid.

"From 2-4 feet of snow can easily pile up in the high country of the coastal range north of Vancouver," Anderson said.

The storm will also be accompanied by strong winds that will quickly ramp up on Friday and linger into the weekend. With winds blowing perpendicular to the coast for a significant part of the storm, waves will rapidly build to dangerous levels for small craft on the open Pacific and hazardous levels on the straits surrounding Vancouver Island and the mainland.

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