2021-22 Holiday Cold Weather Recap

2021-22 Holiday Cold Weather Recap

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A new calendar year has begun, and a week-long cold spell in the Pacific Northwest is ending (at least for the West Side!).  A push of milder air and south wind has begun today, which should lead to classic liquid rain later this afternoon and evening.  This cold weather was felt differently, depending on your region and your elevation.  Here in the Portland-Vancouver area, the cold and snow were rather “weak sauce.”  The event began on the night of December 25, when snow levels dropped close to sea level.  It ended the morning of January 2 with the return of milder air.

TEMPS

Portland Airport only dropped to 25 degrees F on New Year’s Night.  In my Orchards neighborhood the coldest reading on my Android phone was 21, but I’m not sure of the exact source used to determine local weather readings.  That isn’t cold enough to kill hardier plants in local gardens, but it did put them into “hibernation mode.”  My roommate’s winter vegetable beds look a little floppy after a week of snow flurries and temps near/below freezing.

My roommate’s Fava beans! These hardy vegetables use drooping as a protective mechanism during the occasional winter cold blast. It’s not only hardy vegetables, though: Windmill palms survive the snow and cold by curling up the leaflets on each frond. Fatsia plants droop to the ground, even more dramatically than these Fava beans do.

But Portland was right on the “edge” of the arctic airmass, for most of the week-long event.  We got a few nights in the 20s, and daytime highs mostly in the 30s.  Places to our north and east were deeper into the cold air, and saw much colder temperatures (and in many instances, more snow).  For example, the Puget Sound and points north saw a bitter blast of arctic air last Sunday and Monday, while Portland was still in the chilly onshore flow.  Seattle had a daytime high temp of only 23 F last Monday, which was their coldest day in 11 years.  Temperatures in the teens were reported at night across most of northwestern Washington, with the far northern counties (Snohomish, Skagit, Whatcom) plunging into the single digits!

East of the Cascade crest, the coldest weather came on New Year’s Night thanks to clear skies and snow-covered ground.  Pasco Airport dipped to -5F just before midnight, making for a 120-degree spread in the course of the 2021 year (it hit 115 there back in late June).  LaGrande went all the way down to -22, the coldest night in decades.  Most impressive to my eye was the -10 at Hermiston, which is next to the Columbia River.  Even The Dalles made it down to +4…definitely not historic, but a pretty serious freeze nonetheless.

So I think it’s safe to say that this was a “hard” cold event for NW Washington and nearly all of eastern Washington and Oregon.  Not nearly as impressive, absolutely or relatively speaking, for Western Oregon and SW Washington.

SNOW

My neighborhood in Orchards saw measurable snow five nights in a row, beginning on the 25th/26th.  None of the snowfalls were very heavy; most were an inch or less.  The heaviest snow event was on the 27th/28th, when about 2 1/2″ fell overnight.  All in all I’d say we got a total of roughly 5″ during the entire week, though each night’s accumulation melted back quite a bit the following day as temps rose into the mid 30s.  PDX saw 3.5″ snow since Christmas night. Indeed, the airport hasn’t seen a snow-free winter since 2014-15, which is a pretty long stretch.

Snow totals were generally heavier to our north.  Sea-Tac Airport saw a total of 8″ during the entire event, according to NWS Seattle.  And in the Columbia Basin and east side, solid snow cover made the frigid New Year’s Eve possible.

TAKEAWAYS

Some definite things to take away from this episode:

  1.  The “snow shadow effect”.  We had a bunch of cold showers last Saturday night through Monday which dumped a ton of snow in the Coast Range and parts of the northern Oregon Coast.  But Portland and Vancouver saw very little action, due to the rainshadowing (or in this case, snow shadowing) of the Coast Range.  This led to an outburst of hilarious jokes on social media among weather nerds, about whether “blowing up the Coast Range” would help us in these onshore patterns.  Definitely something to keep an eye on in future events, when cold onshore flow is expected.
  2. Climate Change.  With a steadily warming climate we might expect winter snowfall totals in cities like Portland and Seattle to be steadily decreasing in recent years.  Yet there has been no downward trend since the 1980s.  Before then, winters were definitely snowier.  I’m not a professional expert, but I get the feeling that increased jet amplification could explain why we’re still getting cold and snow in the winter, at least some of the time.  But we’re definitely also seeing a trend toward more warm days (50 degrees plus) in December and January.
  3. Extent of arctic air.  This is an important point.  We haven’t seen a “region-wide” arctic blast since December 2013; that’s when cold air overrides the entire Pacific Northwest and frigid temperatures extend deep into southern Oregon.  But we have had arctic fronts move over the area several times since, bringing in enough cold air to get snow & freezing temps in NW Oregon & SW Washington.  We came very close in January 2017, with widespread snow cover and cold east wind coming through the Columbia River Gorge.  That allowed temps at PDX to drop into the low teens.  But it’s not the same as a regional arctic blast.

LOOKING AHEAD

The first full week of January is going to be wet!  Models show two separate atmospheric rivers, one tonight/Monday and another for Thursday.  This is going to also melt a lot of the snow that has accumulated in the Coast Range and foothills.  A Flood Watch has been issued for our region due to the combination of heavy rain and melting snow.  By Saturday the rainfall totals on the GFS look like this:

Credit: TropicalTidbits.com. Between 5-6″ for Portland and nearly 10″ rain for the southern Willamette Valley? That looks like a recipe for some serious flooding.

Thankfully, the weather calms down as we head into the weekend and the 2nd week of January is shaping up to be quite dry!  After nearly a month of active winter weather, I think weather nerds and meteorologists will have earned a little break.

Happy New Year!  -Karl

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