Beginning around 1/14, a strong ridge of high pressure began to form over the Pacific Northwest, and although a few weak systems passing over it have brought a few sprinkles to Western Washington and Oregon at times, the weather is dead calm compared to the extreme mountain snow and river flooding we had to begin the month. Other than some scientific chatter regarding the catastrophic eruption of Hunga Tonga-Hunga Ha’apai, internet weather forums and Facebook groups have been crickets, with only a few intermittent posts about neighborhood observations or interesting weather in different parts of the country.
One thing that has been notable with this ridging is the strength of the inversions over Western Washington, the Willamette Valley, and the Columbia Basin. Take January 16th for example. On the 16th, Paradise Ranger Station at 5,400′ in Mt. Rainier National Park reached 49 degrees with blazing sunshine, while temperatures only reached the low-mid 40s throughout Puget Sound and Willamette Valley and struggled to reach the mid 30s for much of the Columbia Basin.
Why was there such a strong temperature inversion? During the winter, higher latitudes have a negative radiation flux, meaning more radiation is emitted out to space than is received from the sun. And when a ridge of high pressure sits overhead with little atmospheric mixing, the surface radiates heat out to space while receiving very little from the sun. With no stormy weather to bring a new airmass into the area, this persistent ridging allows a strong inversion to form over sheltered basins while the mountains bask in sunshine and springlike warmth.
On 1/16, while Seattle was shrouded in fog w/ highs only reaching 42, Paradise Ranger Station on Mt. Rainier (5,400′ feet) hit 49 and basked in sunshine.
Shows how strong our inversions can be in the winter, when solar angles are low and the surface radiation flux is negative. pic.twitter.com/APeQ7gR8o5
— Charlie Phillips (@GeoduckChuck) January 22, 2022
Thankfully for us (and sadly for Paradise Ranger Station), we may transition to a more typical La Nina pattern towards the end of this month, with pronounced troughing along the West Coast bringing cooler-than-average temperatures, near-average precipitation, and above-average mountain snow. Let’s take a closer look.
Next Week: Persistent Ridging
We currently have a massive ridge offshore with a shortwave trough bringing cool temperatures to the Intermountain West/Desert SW and Santa Ana winds to Southern California. This would be a fire weather pattern for Southern California had they not received 3-4 times their typical precipitation for December. These fast-moving shortwave troughs bring cool, dry, dense air to the Great Basin and create a strong offshore pressure gradient, resulting in strong, downslope, Santa Ana winds as this air accelerates through the Southern California mountain passes all the way to sea level.
Credit: WeatherTogether Models
This ridging will more-or-less stick around for the next week. It’s not quite what we sometimes call a “Death Ridge,” where a ridge of high pressure just sits and sits and inversions build and build, but we’ll see continued low clouds and inversions both west and east of the Cascades. An “Air Stagnation Outlook” is currently in effect for Western Washington from Sunday afternoon through Wednesday afternoon to reflect the potential for deteriorating air quality and persistent low clouds/fog due to the persistent ridging and surface inversions. As the 925mb temperature chart below shows, the inversions will be strongest and deepest over the Columbia Basin and Snake River Plain.
Credit: University of Washington
Those in the Portland Metro Area looking for some east wind action should head out to Crown Point later in the week as the cold pool strengthens. I don’t know if the wind speeds out there will be strong enough to cross the “bring out the news crews” threshold, but I wouldn’t be surprised to see max gusts in the 60-70 mph range.
The Following Week: Cool With Near-Normal Precip
Models still hang on to some ridging on Friday, but most models show a slow pattern change over the weekend, with this ridge breaking down and being replaced by a trough offshore. And by the following week, most models show a return to a typical La Nina pattern like we had for much of December, with persistent troughing off the West Coast bringing northwesterly flow and cooler-than-average temperatures to the area.
Very strong #LaNina signal in both GFS & ECMWF first week of February. Ensembles show persistent troughing off the West Coast, giving cooler-than-average temps and near-average precip. Not particularly stormy but great for mountain snow. #wawx #orwx pic.twitter.com/yWsjdETqyo
— Charlie Phillips (@GeoduckChuck) January 22, 2022
There’s pretty good model agreement here, so I have above-average confidence that the beginning of February will be cool with mountain snow. It’s too early to know how the rest of the month will play out, but with a robust La Nina still in effect and many Februarys over the past decade exhibiting anomalous troughing and significant lowland snow over the Pacific Northwest, I’d be surprised if February was as quiet as the second half of January!
So, to recap… expect continued ridging with slightly deteriorating air quality next week, and the strong inversion building over the Columbia Basin could cause some moderately gusty east winds in the Western Columbia River Gorge towards the latter half of the week. This ridging should break down next weekend, and by the beginning of February I am pretty confident that we’ll experience a more typical La Nina pattern, with cool temps, moderate precipitation, and heavy mountain snow.
