Those of us who have lived in the Pacific Northwest most or all of our lives, used to see February as the  “beginning of the end” of our normal winter season.  Historically it tends to be the warmest of the three winter months, with December and January trading the gold medal back and forth over the decades.  I definitely recall this phenomenon in my youth, so much so that I came to see mid/late February as the de facto beginning of spring.

However…for the past decade or so, this phenomenon has been less true.  As I recently wrote in my decadal climate change blog, February and March are the two months which have actually seen cooler temperatures 2011-2020 than in previous decades.  Four Februarys- 2011, 2014, 2018, 2019 – saw serious intrusions of modified arctic air in the immediate region.  Three of our biggest four snow months were also February 2014, 2018, 2019.  March has also been more ‘wintry’ than normal in 2012, 2019 and 2020.  It seems as though the last 6 weeks of the season- February and early March- have been getting the lion’s share of the action lately.

Sure enough, 2021 appears primed to follow the same course.

We’ve had an extremely warm December and January; actually the 2nd warmest Dec-Jan period in PDX history. Daffodil stalks are getting high and tree buds are swelling, as though spring is just about to commence.  But now we are likely to enter the coldest pattern of the season, with frigid arctic air in the Columbia Basin and a scorching cold, dry east wind coming into Portland via the Gorge.  The action is expected to pick up on Wednesday night or Thursday, but we’re entering the basic “cold pattern” beginning tomorrow.

At 4pm tomorrow (shortly after kickoff in Super Bowl LV), we will have only a few light showers in the area:

But they are rather chilly showers, with snow levels near 1,500-2,000 feet and lowland temps stuck in the low/mid 40s.  That’s because we’re actually on the edge of a massive dome of cold air,  covering all of Western and Central Canada.  The 500mb (3 mile) elevation charts show the cold anomalies:

That frigid air is going to move south, unimpeded just about everywhere east of the Rockies. But this time it looks as though quite a bit of that cold air will also flood into the Columbia Basin. It will be a gradual process Monday-Wednesday before the coldest air (tentatively) arrives Thursday.  By Thursday morning at 4am the upper-level anomalies over North America look like this:

That secondary ‘bulb’ of low pressure off the southern Oregon coast is helping to pull more cold air in from the polar vortex to our northeast.  Here’s the reliable WRF-GFS pressure + 925mb map for Thursday morning:

Holy cow! Anytime you have pink showing up east of the Cascades, it signifies a major outbreak of arctic air.  That pressure difference caused by the cold, dense air is going to drive a very powerful east wind through the Gorge, likely gusting 80-100 mph in places like Crown Point…yay! Time for a frigid trip up there! (Not without a winter vehicle survival kit, though.)

The 850mb temps east of the mountains are plenty cold, around-17 to -18 degrees Celsius:

The only question still up in the air is whether we get precipitation on top of that cold air. The 12z GFS pushed the low into Southern Oregon and California, keeping Portland mostly dry.  Previous model runs brought moisture further north for a snow/ice storm late Thursday into Saturday.  But these things have a tendency to be fickle; we could actually see snow appear and disappear several more times over the next few days.

About the only certainty is that it will turn chilly tomorrow and Monday, and then probably colder by Wednesday night and Thursday.  The most recently available WeatherTogether spaghetti charts for The Dalles, is the 06z from early this morning. Notice the very strong signal for a blast of cold air late in the week:

So make sure you have blankets and survival food in your car, and brace for dangerous wind chills later in the week.  Based on the current maps,  I bet Portland will only top out in the low to mid 30s Thursday,  with wind chills likely in the teens.  OUCH!

…And once again, we will be able to geek out about how February was the coldest month of the season.   Given that December and January were as warm as a normal February,  all we need to do is end up slightly below normal this month; which is a likely feat after the events of the coming week!

Stay tuned in the coming days to find out about the question of snow in the Portland metro.  -Karl