Winterlike Storm Threatens Major Flooding in Northwest

By Alex Sosnowski, Expert Senior Meteorologist

September 26,2013; 8:51PM,EDT

 

 

The first powerful winterlike storm of the season will take aim on the Pacific Northwest Friday into Monday with potentially disastrous flooding, damaging winds and dangerous seas.
The storm will cross Alaska Thursday with gusty winds, rain and mountain snow, but will grow into a monster over the Gulf of Alaska Friday, where it will stall over the weekend. Winds of 40 to 60 mph will roar over the ocean raising 15- to 30-foot seas.
As the storm expands southward and eastward, it will spread heavy rain, flooding, travel delays, high winds, pounding surf and rough seas first to British Columbia, then to Washington and Oregon and finally to northernmost California.

The worst conditions are likely to stay north of California, and will instead target areas farther north on Saturday with another heavy dose possible later Sunday into Sunday night.
Rain, Flooding
Enough rain will fall to cause urban flooding and small stream flooding, rockslides and rises on the major rivers. Flooding along the short-run rivers off the Olympics and Cascades is possible later this weekend.

Rounds of windswept rain, urban flooding and poor visibility will lead to travel delays along the I-5 corridor and potentially at Seattle-Tacoma International Airport and others.
The heaviest rain, on the order of 4 to 8 inches (up to 200 mm) will fall on the southwest-facing slopes of the Olympics and Cascades in Washington and the Vancouver Island Ranges Coast Mountains in British Columbia.

Elsewhere, from western Oregon through western British Columbia, a general 2 to 4 inches of rain is forecast. Much less rain will fall over central and eastern Oregon, Washington and British Columbia, but some rain will fall on these areas. Enough rain could fall to end the risk of wildfires once and for all this season.
Rounds of heavy rain and gusty winds may be a factor for college football games in Seattle, Eugene and Corvallis, Ore., and other locations in the region. The Huskies, Ducks, Beavers and Cougars are all at home Saturday.
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Wind
South-to-southwest winds can be strong enough to down some trees, cause minor property damage and lead to power outages.
Wind gusts along the northwestern part of Vancouver Island and parts of the Washington and British Columbia coasts can reach between 50 and 60 mph. Gusts can be locally higher on the ridges.
Because of the wind direction from the south and southwest, this will not be the worst-case scenario for Seattle, Tacoma and Olympia, Wash., and Portland, Ore.
Snow
Unlike many storms in the winter, snow levels with this storm will remain rather high ranging from 7,000 to 8,500 feet.
According to Meteorologist Brian Thompson, "Accumulating snow will generally remain above the passes, including Snoqualmie and I-90."
Snow levels will drop during the latter stages of the storm, Sunday night and Monday, when wet snow can mix in over the higher passes. However, hikers should avoid the peaks in the Cascades throughout the storm, where blizzard conditions are likely.
Seas
Small craft should remain in port or within protective areas of the bays and straits of Georgia and Juan de Fuca.
While seas will be very rough offshore, the south-to-southwest wind driving the waves will not bring the worst-case scenario to most coastal areas in terms of pounding surf and coastal erosion.
In some cases, the wind-wave action will be parallel to the coast. However, the worst effects are likely to be along the upper half of Vancouver Island that is exposed to south to southwest winds.
Record Wet September Possible
Enough rain could fall at Seattle-Tacoma International Airport for this September to rank in the top-five wettest on record. According to the National Weather Service, the wettest September on record at the airport was in 1978, when 5.95 inches fell. As of Thursday, Sept, 26, 2013, 3.03 inches of rain have fallen at the site. This September could be the new record-holder.
Similarly, Olympia Airport, Wash., could achieve a top five or record rainfall for September. In 1978, the month brought a record 7.59 inches. The fifth-wettest September was in 1977, when 4.58 inches fell. As of Thursday, 3.92 inches of rain have fallen at the site.