Pacific northwest winter storm

[WXBUFFJIM]

Good evening everyone. A big winter storm followed by possible sea level river flooding in the Pacific northwest. Gale warning are also in effect for the Washington and Oregon coast tonight. This is storms watch given the winter and flood scenarios.

Getting right to the facts starting with the current obs as of 10 PM PST. It's light snow with a temperature of 26 degrees at Hoquiam, Washington, 27 in Astoria, Oregon, and 9 above zero in the Dalles. It's overcast and 24 degrees in Seattle, 20 in Portland, 18 in Troutdale, and minus 3 in Stampede Pass on I 90. I 90 won't be a fun ride at all over the next few days. If you can imagine how bad it will be at sea level, try heading up the mountains. I sure wouldn't with the avalanche dangers increasing.

On radar tonight, things are starting to crank up near Portland and Seattle with respect to precipitation. Some of the initial precip will probably not hit the ground. However it won't take long to saturate the low levels and get some good snow coming down overnight. Snow will likely be heavy at times ven at sea level in Seattle and Portland with the mountains getting it much worse obviously.

Breaking down accumulation for snow, by Tuesday evening expect total snow accumulation of 4-8 inches in Portland in the downtown area, 2-4 inches on Astoria, Oregon, 8-12 inches in Troutdale and 6-8 inches in Seattle with more to the east and less to the west of the city. The Washington coast will likely also see 2-4 inches of snow. So a significant snowstorm for this part of the country. The Cascades, Olympic Mountains, including Mount Baker will likely see snow measuring several feet before all is said and done. Stampede Pass will see moderate to heavy snow throughout this event with no changeover expected. That's why if it's bad in Seattle and Portland, I 90 won't be any better, it will be worse through those passes, much worse. Best bet is just stay home tonight and tomorrow in Seattle and Portland and points east into the cascades. It's not gonna be pretty. Combine the heavy snow with strong gusty winds, natural avalanche danger is quite high for the mountainous areas. Cold wind chills are also expected with this type of storm.

After the snow changes over in Seattle and Portland, there is a huge concern, especially east of Portland in the Troutdale area and the Dalles for significant and damaging ice accumulation. Some places could potentially lose power with this type of snow and ice on top of snow setup. Then with slushy snow covered roads and rain falling tomorrow night on top of that in Seattle and Portland, travel will be even more dangerous. Best bet is forget travelling until Wednesday at the earliest unless it's an absolute emergency in which case 911 is the best option.

Now the question is why the winter storm in Seattle and Portland? A tremendous cold high pressure system has made it into the lower 48. This arctic plunge associated with the high is funneling through the Columbia River Gorge and into Portland tonight and through the Stampede Pass and into Seattle. With this east wind trajectory, that's where we sweeze out maximum amounts of snowfall in the Sea Tac and Portland area. At the same time this colder air is moving in, a huge moisture plume of Pacific moisture is moving into this colder arctic air generating the beginnings of what will be heavy snow even at sea level and coastal locations. The changeover will occur slowly from west to east during the day Tuesday. The further east you go inland, the heavier the snow. The further west you go near the coast, the less the snow and the verifies with the forecast totals. I mentioned them earlier and will mention them again at the bottom. Be safe and just stay home tomorrow if you feel the need to. From my chair here, this is not gonna be pretty for travelers.


SNOW ACCUMULATION FORECAST

SEATTLE: 6-8"
TACOMA: 6-7"
STAMPEDE PASS: 18-24"
PORTLAND" 4-8"
TROUTDALE: 8-12"
THE DALLES: 12" plus
ASTORIA, OR: 2-4"
HOQUIAM, WA: 2-4"

Cascade mountain peaks: 2-4 feet potentially.

Jim

[JCT777]

Nice post on the Pacific NW snow event, Jim.