A long plume of moisture stretching from near Hawaii, a version of an atmospheric river known as the Pineapple Express, will target British Columbia and parts of Washington beginning this weekend and lasting into early next week.
Heavy rain-induced flooding and an increased avalanche risk could pose a threat to lives, property and travel across the region.
Memories of December’s torrential rain and flooding remain fresh for people in Western Washington. While the atmosphere has provided a bit of a respite from these conditions in recent days, the weather pattern is lining up to deliver another round of heavy rain that may escalate into significant flooding.
The heaviest rain is expected on Vancouver Island in British Columbia, where 4 to 8 inches may fall, with higher amounts in some locations. Heavy rain will also impact northwestern Washington and the British Columbia mainland, especially along the west-facing slopes of the Olympic and Cascade ranges and the coast mountains.
The plume of heavy rain began in central British Columbia and southeastern Alaska on Friday and is forecast to expand southward through the weekend.
In coastal areas, heavy rain could cause rapid rises on small streams and short rivers, leading to flooding. In urban areas, including the Interstate 5 corridor near Seattle and Bellingham, and the Vancouver metro area, flash flooding of streets and highways is likely.
Snow levels will generally remain above Washington’s mountain passes during this event. As rain falls at mid-level elevations and adds weight to existing snow, the avalanche risk will increase. At lower elevations, heavy rainfall will increase the risk of mudslides and other debris flows.
Areas farther south, especially in Oregon, may receive little or no rain from this pattern. Some of the worst conditions may occur farther north, where there is deep snow on the ground.
Additional storms are expected next week, bringing more rain to low elevations. Rain and above-freezing temperatures will melt more snow, increasing the risk of flooding in Juneau and other parts of southeastern Alaska.
Beach hazards statement
The National Weather Service has issued a beach hazards statement Friday morning through Monday afternoon with sneaker waves possible along the Southwest Washington coast.
Sneaker waves can run up significantly farther on a beach than normal, including over rocks, logs, and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning.
Keep children and pets close and away from the surf zone. Keep off of jetties, rocks and logs near the surf zone. If you see someone swept into the sea do not swim in after them. Call 911 and keep an eye on them until help arrives. Stay farther back from the ocean than you think is necessary.
Threat of river flooding
Moderate to heavy rainfall is expected in the headwaters of the Skokomish River beginning late Saturday morning and persisting through at least Monday night. Rainfall totals of 2.5 to 4.5 inches are forecast for this time frame.
Snow levels will rise from around 4,500 feet Saturday to over 7,000 feet Monday. The river will begin rising Saturday night potentially reaching flood stage of 16.5 feet late Sunday night. The river is currently projected to crest near 17.5 feet Monday afternoon.
