The calendar still says September. However, a November-like barrage of powerful storms is taking aim on the Pacific Northwest this weekend.
Numerous cities already got socked on Saturday as an initial round of heavy rainfall and high winds pummeled Washington, Oregon, northern Idaho and northwest Montana.
At least three cities broke all-time September calendar-day rainfall records on Saturday:
- Seattle-Tacoma Airport: 1.71 inches (previous record 1.65 inches set Sept. 22, 1978 and Sept. 30, 1953)
- Olympia, Wash. Airport: 2.93 inches (previous record 1.67 inches set Sept. 17, 2010)
- Astoria, Ore.: 3.16 inches (previous record 2.67 inches set Sept. 16, 1997)
Gusty winds produced numerous broken tree branches, downed power lines, and traffic control lights throughout the downtown Portland area on Saturday night. Over 25,000 customers were without power Saturday evening, according to PGE. Sustained winds of 50 to 60 mph have been reported throughout the region, and 70 to 75 mph gusts have been observed in Garibaldi, Ore.
Another powerful impulse will arrive later Sunday into early Monday with additional high winds and heavy rain. Interestingly enough, this second round appears to have received an injection of remnant moisture and energy from the former western Pacific Typhoon Pabuk.
That said, periods of showers, wind and lowering snow levels will linger Monday into at least Tuesday, as pulses of energy rotate around the bullish upper-level jet stream dip into the Northwest.
Heavy Rain/Flooding Threat
Latest Radar
Storm Total Rainfall Forecast
By early Monday, rainfall totals from 5 to 8 inches are possible along the southwest-facing slopes of the Olympics and Cascades of western Washington and western Oregon. Rainfall totals over five inches are also expected along the coastal ranges of Oregon. These figures include the rain that has already fallen.
General three-inch-plus totals are expected along the Interstate 5 corridor of Washington and Oregon, including Seattle, Portland, and Eugene.
Parts of northeast Washington, the Idaho Panhandle and northwest Montana may pick up 1 to 3 inches of rain as well, with locally higher amounts.
This rain will likely send some rivers into flood stage this weekend, including the flood-prone Skokomish River north of Olympia. Fortunately, as the National Weather Service in Portland, Ore. notes, pre-storm river levels are running low, since we're coming out of the summer dry season.
However, NWS-Portland also notes with leaves still on trees, the potential exists for clogged storm drains and urban flooding. Mudslides and rockslides are also possible in a few areas.
Snow levels will also fall through the period, possibly as low as 4,500 feet in the Cascades and 5,500 feet in the far northern Rockies (northern Idaho/northwest Montana) early next week.
High Wind Threat
High Wind Alerts
The combination of deep low pressure diving southeastward from the Gulf of Alaska and a powerful jet stream punching in will lead to a large area of high winds not solely at the Pacific Northwest coast, but also well inland as far east as the lee slopes of the northern Rockies.
The strongest winds will accompany each frontal system's arrival. Here are some forecast wind gusts by region:
- Washington/Oregon coast: Gusts over 55 mph, possibly reaching 80 mph Sunday along Ore. coastal headlands through late Sunday
- I-5 corridor: Occasional gusts over 50 mph through early Monday
- Eastern Wash./eastern Ore./northern Idaho: Gusts from 50-60 mph particularly late Sunday/early Monday
- Western Montana: Gusts to 80 mph along Rocky Mountain Front, 50+ mph gusts elsewhere through Monday
- For information specific to your area, check your local forecast.
Overall, the combination of heavy rain and strong winds will lead to some downed tree limbs, weaker trees, and power lines, leading to some power outages. Dangerous crosswinds will also be a concern particularly on north-south roads.
In addition, expect seas to build to 20-25 feet near the Washington and Oregon coast by Sunday.
Snow
Pacific Northwest Snow
In addition to the issues with heavy rain and high winds, parts of the Cascade Mountain range will also be dealing with wet snow to boot. Forecasts indicate that as much as 6-8 inches of snow will fall in the higher elevations, especially above 6,000 feet. Snow levels could drop to below 4,000 feet for the northern Cascades.
Travel, especially on the higher passes and roads will be made a bit dicey through Monday. Use caution if you have to drive over the Cascade Range.
http://www.weather.com/news/weather-forecast/northwest-rain-wind-weekend-washington-oregon-20130926
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