The bright sunshine today was nice wasn’t it? It always raises my mood this time of year. In December we “hit bottom” west of the Cascades with respect to the cold season. It’s our darkest, cloudiest, and typically our coldest month of the year
Of course that is the average. In some years January is colder (2017).
Right on cue a very long period of cold east wind has begun this evening. Why? A split flow in the jet stream sends a wet system into California this week, keeping us all dry. There will be no weather systems moving through the Pacific Northwest through at least Friday.
We have long winter nights this time of year. The airmass east of the Cascades in the lower elevations loses more heat than it gains during the day; not enough daytime sunshine to overcome the overnight cooling. The result is strong high pressure centered east of the Cascades through at least next Monday!
There is only one sea level gap through the Cascades and that’s the Columbia River Gorge. The cool airmass is less than 4,000′ thick so this will be what we call a GAP WIND. Air will be flowing through this gap. We don’t get air flowing up and over the mountains in this case (a downslope wind), so only those near the mouth of the Gorge will feel the wind. That’s the central/east Portland metro area and hills around town too.
Right now the wind is just getting started with gusts around 60 mph at Vista House and 50 in Corbett. Easterly breezes have begun to show up in the West Hills and east metro too. Pressure gradients are up to around 4 millibars from The Dalles to Portland. Models push it to 8 millibars by Tuesday morning and keep it in that general range all the way through next Monday! This is going to be a long episode of cold wind blasting through the west end of the Gorge as the cold pool deepens east of the mountains.
Peak gusts will reach 35-50 mph east metro, 60-70 mph western Gorge, and of course 100+ on the Vista House steps either starting tomorrow or Wednesday.
The dry air coming in from the east will minimize morning fog in the metro area tomorrow. Then eliminate it the rest of the week. Spots that go calm the next 3-4 nights will be COLD.
- Windy areas will likely not drop below 32 all week.
- Calm areas will be down in the 20-25 degree range each night
- The coldest outlying areas (Vernonia, Yacolt, etc…) could drop down into the upper teens.
That brings up an interesting point. This pattern COULD produce the coldest temperature of the winter. 5 of the past 9 winters the coldest temp was in either November or December. Of course we never know until we get to late February.
Try to stay warm this week and stay out of the wind if you can.
Chief Meteorologist Mark Nelsen