A Review of the January 12-13, 2021 Windstorm

It’s been a while since we had a significant, regionwide, winter windstorm hit the Pacific NW. The last major windstorm to hit the Inland Northwest was the 11/17/2015 windstorm, which brought an extended period of 60-70 mph gusts to Eastern Washington and devastated electrical grids around the region. Avista Corporation, a utility headquartered in Spokane that serves much of Eastern Washington and Northern Idaho, called the storm the “largest crisis Avista has experienced in the company’s 126 year history.” The 11/17 windstorm also caused extremely strong westerly winds through the Columbia River Gorge, caused widespread river flooding over Western Washington and Oregon, and gave record high temperatures to many places east of the Cascades – all of which also occurred in the windstorm that swept through the Pacific Northwest Tuesday night & Wednesday morning. The last major windstorm for Western Oregon was the December 11, 2014 windstorm, which gave a 67 mph gust to Portland Int’l Airport and also caused extensive damage to the electrical grid.

Portland “only” recorded a gust of 50 mph with our most recent tempest. However, the Tuesday night/Wednesday morning storm knocked out power to approximately 95,000 Portland General Electric customers. The Inland Northwest saw over 100,000 outages and, like the November 2015 storm, 60-70 mph gusts over a wide region. And Western Washington was absolutely clobbered by this week’s storm, with 559,000 customers losing power amidst gusts to 50 for the Seattle metro area and gusts as high as 70 over the Northern Interior and along the Strait of Juan de Fuca.

Why was this storm so much more impactful than expected? Why were there so many outages despite strong but unremarkable winds, particularly for NW Oregon northward to central Puget Sound?  And how could this storm have caught us so flat-footed?

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Storm Synopsis:

This storm can best be described as a prolonged “atmospheric river” that was capped off by a stronger-than-expected, compact, and rapidly intensifying low-pressure system that rode along this atmospheric river and slammed into the Olympic Peninsula Tuesday night. An “atmospheric river” is a long, narrow filament of moisture that extends from the subtropics to the midlatitudes, and because warm air can hold more moisture than cool air (via the Clausius Clapeyron relationship), atmospheric rivers tend to be far wetter than systems that lack a subtropical connection. In addition to bringing heavy rain rates and high snow levels, atmospheric rivers tend to be relatively stationary, which further increases their total rainfall and potential for river flooding, landslides, and other rain-related hazards. Atmospheric rivers are also often associated with a strong low-level jet, which further enhances precipitation on the windward slopes of mountains and in some cases can result in extraordinarily strong winds, particularly along the coast. The best example of this was the December 2-3, 2007 atmospheric river, which brought a 24-36 hour period of hurricane-force gusts to the Washington & Oregon Coasts and left catastrophic damage in its wake.

As the radar image below shows, this atmospheric river was already bringing copious amounts of moisture to Western Washington by Monday morning.

While Seattle started the workweek on a soggy note, folks in Western Oregon were treated to a spectacular sunrise Monday morning. I took this picture looking southeast from my apartment in the Hollywood District of Portland. The adage “red sky in morning, sailors take warning” has some scientific validity, as red skies in the morning mean that it is sunny over the eastern horizon but cloudy over the western horizon. Since our weather comes from the west, a red sky in the morning can mean a storm is arriving, while a red sky in the evening means a storm is departing. This adage sure was prescient on Monday!

This rain persisted over Western Washington for most of Monday. It wasn’t until Monday evening that this rain finally moved into Portland. Still, Portland measured 0.57″ inches of rain for the day, the vast majority after 5pm. Olympia, which saw rain for nearly the entire day, measured 1.46″ – over 2.5 times the amount that Portland experienced.

But both Olympia and Portland would see even heavier rain on Tuesday as the atmospheric river intensified and stalled over Northwest Oregon and Southwest Washington for the entire day. Portland received 1.94″ of rain on Tuesday, its highest daily total since we measured 2.13″ on October 21, 2017. Olympia, which didn’t experience any sort of rainshadowing from mountains upwind, saw 3.04″, another daily record. But with a strong low-level jet helping enhance rainfall on the western slopes of the Cascades, Coast Range, Willapa Hills, and Olympics, our totals here in the lowlands were absolutely dwarfed by those in the mountains. Meanwhile, locations on the lee slopes of the mountains saw significant rainshadowing, receiving 10% or less of the precipitation measured on the windward slopes.

The above image shows the “storm total rainfall” from midnight Monday to midnight Thursday. Note some of the extreme totals over the Olympics, Willapa Hills, Northern Oregon Coast Range, and Northern OR/Southern WA Cascades. Meanwhile, areas in the lee of the Olympics saw less than an inch, and many places east of the Cascades saw less than 0.10″ inches. Incredible.

There were two main periods of rain on Tuesday – one from midnight through 1pm (as an extension of the rain that began Monday), and another from around 6pm to midnight that was associated with the developing low-pressure system that rode along this atmospheric river into the Olympic Peninsula. After the trailing cold front moved through, heavy rain rapidly tapered to light showers, winds calmed dramatically, and temperatures plummeted, marking an end to our stormy, subtropical, atmospheric river pattern and a return to a more seasonable, calmer temperate pattern with weak onshore flow off the Pacific.

The Surprise Windstorm

We knew that this atmospheric river was going to drop a tremendous amount of rain and cause problems with landslides and river flooding. However, the winds with this tempest far exceeded our expectations. Nearly every model was going for simply breezy conditions to accompany this atmospheric river. The one exception was the European model, which was adamant that we would have a moderate windstorm with gusts in the 35-50 mph range.

There were two main surges of wind, and both were associated with frontal passages and approaches. The first surge occurred early Tuesday morning when the storm’s strong warm front moved inland, and the stronger, second surge occurred Tuesday night and very early Wednesday morning as the storm’s trailing cold front approached, with the strongest winds occurring essentially right at the frontal boundary. I lost power with both fronts – I had a 1-second flicker around 6:30 am that reset all my clocks (some may not call this a power outage, but it passed the “clock test” so it is in my book!) and I lost power sometime Tuesday night/Wednesday morning, as my clocks were once again off when I woke up at 4am to begin my work day. These were strong fronts by Pacific Northwest standards – note the dramatic temperature rises and falls with these fronts in the temperature graph below, and note how well they align with the trend in wind speeds.

Lessons Learned:

I’ve always preached on this blog that a forecast is only as good as how well it is communicated. For example, say you absolutely nail a “marginal” snow event, with a wet, non-sticking snow over downtown Portland. However, you don’t explicitly state that this snow would not stick to the roads and therefore have negligible impacts on travel. In that case, people may see that snow is in the forecast and jump to the conclusion that another “Snowmageddon” is on the horizon, resulting in the grocery stores being stripped of kale, cage-free eggs, and organic soy milk! Then, when a truly impactful snow/ice/freezing rain storm slams into the area and makes roads impassable, people may disregard warnings ahead of time, resulting in horrific traffic backups when the perfect forecasts come to fruition.

In this event, I think there were two primary things that could have been better communicated to the public. The first was that we underestimated the “compounding effect” that saturated soils from all the heavy rain would have on tree falls and damage to the electrical grid. Saturated soils lose their cohesion, and many Pacific Northwest trees have shallow root systems, as the ample precipitation that we receive west of the Cascades means that these roots can get all the water they need without reaching deep underground. The combination of shallow-rooted, leaved conifers in loose soils means that these trees can experience a lot of force under only moderate wind and topple completely, resulting in significant disruption to the electrical grid. This was one of the primary reasons why the Hanukkah Eve Storm was so destructive – not only did it carry extreme winds, it occurred in the wake of one of the wettest Novembers on record for the Pacific Northwest and capped off an extremely wet week. The below image, taken from Wolf Read’s “Storm King” website, shows a toppled Douglas Fir in Avery Park, Corvallis, from the Hanukkah Eve Storm. Note how the soil has completely fallen away from the shallow roots of the fir.

The second lesson is that we can’t let any particular hazards from a storm “overshadow” and “minimize” other impacts from the storm, as the sum of the impacts can be greater than the parts. With this storm, we had very high confidence in heavy rain that would cause significant flooding and landslides and we effectively communicated this threat. However, the focus on flooding and landslides unfortunately came at the expense of any focus on wind, when in reality, it should have amplified the focus on wind due to soil saturation. While it is true that there is only so much information TV meteorologists can put in a 2-minute TV newscast (as a KOMO News intern who’s practiced in front of a green screen, I’ve experienced this first-hand!), we have other methods of disseminating this information, such as Twitter/Facebook, weather blogs, and the more extended “selfie stick” videos that some meteorologists now do and post to either their websites or social media, and I don’t think there’s much of an excuse for not correctly highlighting the small but very real potential for a highly disruptive windstorm.

Forecasting is a probabilistic exercise by nature. When we run weather models, we take a look at all the different solutions, discern what solutions are most likely based on model consensus, prior model performance, and climatology, and emphasize these solutions while still highlighting the risks associated with the less probable, but still possible, solutions. Unfortunately, humans are poor at understanding probabilities, leading to an incongruence with the nature of forecasting and human psychology. Forecasting will always be an exercise in quantifying uncertainties and we need to find better ways to communicate forecast confidence and the range of possible outcomes/impacts to the public. I think we’ve made great strides in doing this, and the National Weather Service offices in particular (I’m most familiar with Seattle & Portland, but all do a fantastic job) are very skilled at highlighting the potential range of impacts from any given storm and the outcomes of these impacts. However, I believe that some other people/organizations tend to take a more “sensationalist” view to upcoming weather events in an attempt to drive traffic to their websites/posts. The weather directly impacts people’s lives and “hyping” the forecast for personal gain is irresponsible.

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The Week Ahead:

We had a stunningly beautiful day today, with bluebird skies and highs making it up into the low 50s. Although the low 50s are only 5 degrees above-average, the extra solar radiation sure made it feel warmer. My apartment faces south and experiences quite a “greenhouse effect” during sunny days, and I never had to turn the heat on today yet am writing this blog in shorts and a t-shirt! We can thank a massive ridge of high pressure just offshore for such a beautiful mid-winter day.

If you weren’t able to get outside and enjoy the sunshine today, don’t despair! Tuesday will also feature mostly sunny skies with highs in the low 50s, though we’ll see increasing high clouds in the afternoon and evening as a weak trough slides down from the NW on the back side of this ridge. This trough will usher in a much cooler airmass on Wednesday with highs only making it into the mid 40s, but I still think we should remain dry.

A weak low pressure system could follow on Thursday and bring a few showers to the Pacific NW Thursday evening, but I believe most of the energy from this weak system will be directed south towards Central and even Southern California. This is wonderful news for them; they have been bone-dry for the last few weeks even as we in the Pacific Northwest have experienced record-wet conditions, and are currently in the midst of an extreme Diablo/Santa Ana event that has triggered Public Safety Power Shutoffs throughout the state.

By Friday and especially on Saturday, a ridge of high pressure is expected to rebuild, once again giving us unseasonably calm and sunny conditions. The first half of January was the wettest on record for many locations in the Pacific NW (and it’s not like the rest of the news has been a bundle of joy either!), so we definitely deserve this reprieve from the stormy weather of late. Remember – Wednesday and Thursday will be cloudy and cooler-than-average and Thursday could feature a few rain showers, so I don’t expect spectacular weather the entire week. But in mid-January, we’ll take whatever sunshine we can get!

However, a major pattern change to an extended period of cooler and wetter-than-average weather is expected to occur on Sunday. The Friday/Saturday ridge will weaken and move inland, and a deep trough will take its place. This trough will open up the door for a parade of cool, wet systems to impact the Pacific NW from the northwest. This is an extraordinarily efficient pattern for mountain snow not only due to the cool/wet nature of these storms but because they will arrive nearly perpendicular to the Cascades, resulting in very efficient orographic (terrain-induced) enhancement of precipitation on their windward slopes.

Take a close look at the upper-level pattern above, and compare it to the “classic” La Nina pattern below. The pattern above is a textbook La Nina pattern, with a big ridge of high pressure in the Central Pacific, a trough over British Columbia and the Pacific NW, and a cool, wet, storm track from the NW.

We have not seen such a pattern this far this winter. We’ve certainly been wetter-than-average, but this rain has been due to a series of warm atmospheric rivers moving into the area. And as Fox 12 Meteorologist Mark Nelsen pointed out in his most recent blog post, the first half of “meteorological winter” (which goes from December 1 to February 28/29) has been the warmest on record for Portland. The typical cool/wet La Nina pattern usually doesn’t set up until January and in many years is delayed until February/March, so as a skier, salmon fisherman, and renewable energy fanboy, I’m holding out hope for a cool/wet 2nd half of winter and spring. And even if you don’t ski, fish, or believe in global warming, ample snowpack will still go a long ways towards improving our drought and decreasing fire danger over the summer.

But what about the lowlands? Unfortunately for snow lovers, I think lowland snow is unlikely even during the week following our pattern change on Sunday. To get lowland snow, you typically need cold, northerly or northeasterly arctic air to move into the Pacific NW and then have some Pacific moisture move over the top of it. Instead, we’ll see cool, persistent northwesterly flow. This pattern can bring snow down to 1000-2000 feet but is not a favorable pattern for snow at sea level. However, it’s still too early to completely rule out the chance for a few snowflakes next week, particularly if we see a particularly heavy band of showers move over the areas just before sunrise.

Thanks for reading and please share if you found this post at least mildly informative and entertaining! Do some snow dances and hopefully our dreams of white will come to fruition.

Charlie