Wind and cold, calm and colder

After a very warm end to 2023, 2024 has taken quite a turn to the cold side in Southeast Alaska, and there are some interesting meteorology lessons in this cold snap.

The cold weather in Southeast Alaska the past few days leads me to compare it to usually much colder places in Alaska. For instance, the lowest temperature so far in 2024 in Juneau has been plus 2F (-17C), same as in Kaltag on the middle Yukon River! Ketchikan has been as cold as Teller at 5F (-15C), Craig is tied with Anchorage (12F/-11C), and Sitka has seen 16F (-9C), the same as usually much colder Adak (though Adak is ~350 miles farther south than Sitka, about the latitude of the south tip of Haida Gwaii). Gustavus matched Kotzebue, north of the arctic circle (-5F/-21C) and Haines with Kiana at -11 (-24C). The coldest recorded temperature in SE this month has been -15F (-26C) at the Haines Border station, which equals the coldest low in McGrath, one of the coldest spots in the interior. OK, I’ve had my fun. I realize that we’re only looking at a 12 day period. Going back just a bit in time reveals that McGrath was -45F (-43C) on boxing day (Dec 26), Kaltag -44 (-42C), etc. But is shows you that every town can have their few days of meteorological fame.

After a very mild November for virtually the entire state, December cooled off in the central and southwest parts, leaving well above average temperatures for the Arctic coast, northeast interior, and the panhandle.

For more on the December picture try theses posts from the excellent blogs by Rick Thoman and Richard James respectively:
https://alaskaclimate.substack.com/p/december-2023-alaska-climate-summary
http://ak-wx.blogspot.com/2024/01/december-climate-data.html

By the 2nd week of January, the unrelenting series of low pressure systems slamming into the coast with their warm and wet weather were pushed back by super strong high pressure over the Yukon Territory. Look at these two surface maps, the first in from Jan 4th when the panhandle was in the mid 30s to upper 40s with rain to the south and heavy snow in the north. The second is from a week later, the 11th, during the first serious cold snap for Southeast Alaska this winter.

Notice how on the 11th the low in Canada is much stronger and much farther southwest than it was — really pushing up against the massive coastal mountain barrier. The extension of this same high has pushed arctic air south through British Columbia, Washington and even into Oregon where, as I write this (1/13), Portland, OR is enduring temperatures in the teens, moderate snow, sleet, and winds gusting over 40 mph. They are also at risk of freezing rain — an infamous Portland ice storm — due to warm moist air from a low approaching the coast. A little gift from Alaska. (You’re welcome.)

So, if Portland is that cold and nasty, Seattle, to its north, ought to be colder, right? Well, if you’ve watched Pacific Northwest weather for very long you’ll know that often it’s not the case, and that holds true this time. The reason is the proximity of the most substantial break in the coastal mountains: the Columbia River gorge. It not only allows the cold, continental air to reach the city, often colliding with a warm, moist ocean air mass, but it channels the wind, increasing its velocity to several times what it would otherwise be. I mention this because it is so crucial to understanding Alaska weather.

Back up in Alaska, where there are even more imposing mountains, even closer to the coast, the blocking and channeling of various air masses is epic. I’ve written on this several times, so for more background I’d recommend these previous posts:
https://williwaw.com/2012-01-20/the-highly-channeled-winds-of-coastal-alaska/
https://williwaw.com/2013-02-01/two-kinds-of-cold-in-alaska/
https://williwaw.com/2010-11-16/pressure-extremes-and-migrating-high-winds/

Also, my 2024 Alaska Weather Calendar has a 2-page spread on wind in Alaska, with cool graphical examples of the channeling phenomenon. BTW, there are some great discounts right now on the calendars, especially if you buy more than one (like for a friend?). OK end of commercial, I promise.

Back to the current situation. The high pressure keeps the lows at bay and also causes the air in the high to subside (sink). These two factors are good at clearing the sky of clouds as you can see in this wx cam shot looking from Haines towards Skagway (just hidden by the mountains). Nicely catches that early evening alpenglow, don’t you think?

As the inland high pressure tries to push the air toward the oceanic low pressure, the mountains get in the way. This enhances the pressure gradient in the area of the mountain barrier, and the increased pressure’s going to force the air to get to the low pressure, one way or the other. Kind of like if you were decorating a cake with one of those cone shaped frosting bags (piping bags) with a nozzle on the end. If it’s not coming out well, you’re going to just squeeze harder until it goes through. The air does a similar thing. The mountains are in the way, and gravity works against the dense air getting pushed up and over. Eventually, though, it is going to squeeze through gaps in the barrier (valleys and passes) and get accelerated in the process. Sometimes, with enough pushing, it does go over the top. Here’s a graphic.

Note about the “increased precipitation” marked on the graphic: during a high pressure situation the continental air is so dry there’s not going to be any precipitation. © Jim Green

How exactly the wind flows through the mountains — where it be strong or weak or calm — depends on the orientation of the pressure gradient with respect to the gaps it might flow through, or ridges it might flow over. In the big picture, with high pressure over the continent and low pressure over the ocean (very common in winter), the wind tends to flow out of every pass or valley it can find: this is commonly called an outflow situation. Again, the details are complex and interesting.

In this case, the wind at the Haines airport went unusually calm for an unusual long (~40 hrs) period. The Haines airport is near the lower end of the Chilkat Valley, which is one of those channels whence the wind finds its route from the interior to the low pressure over the ocean. It just happens that the valley is oriented west-northwest/east-southeast, with its west-northwest end being the interior end, ie the upstream end. So the resulting outflow wind comes from the west-northwest, and is quite reliable. But check out the long calm period shown on this graph:

Now, compare it to nearby Skagway for the same time period. (note: the vertical axis is different; Haines’ graph goes up to 32 mph while Skagway’s goes up to 48 mph, since the winds were higher.)

Skagway’s channel, (coming over through White Pass) is oriented roughly north/south, approximately 90 degrees different from the Chilkat Valley. Usually, outflow winds will flow down both valleys at the same time. Often the direction of the pressure gradient, or in different jargon, the alignment of the isobars, will favor one over the other and the wind will be stronger at one town (usually Skagway! Sorry to remind you of that, Skagway neighbors). Occasionally, when the pressure gradient is aligned just right, one town might go calm for a while. In this case Skagway had light winds with periods of calm early in the graphed time period, then they came back, up and down for a while before building to ~25 mph with gusts to around 40. Soon after Skagway started blowing again, is when the ~40 hr calm/near calm period began at the Haines airport. Later both towns had strong winds, which along with the now-colder temperatures brought wind chills down to around -20F for Skagway and -25 to -35F for Haines.

The combination of the cold air mass initially brought into the lower valley by the outflow winds, and the clear, calm period promoting strong radiational cooling allowed Haines airport to get down to -11F, the coldest reading since January 2008. Initially, the wind kept blowing in downtown Haines (just a 1-2 miles east of the airport), keeping it somewhat warmer, but the cold, calm bubble did eventually encompass at least the west side of town, where -11F was also recorded at the Haines #2 coop station.

What’s ahead?

Even in a strong El Niño year, such as we are currently experiencing, there can be cold snaps, and sometimes, the weather can flip for extended stretches of the winter. For SE Alaska, El Niño winters tend to be warmer than average, with more of the precipitation rain instead of snow. But for the foreseeable future for the panhandle (about 7-10 days with steadily decreasing confidence throughout that period), it looks like pretty good odds for a continuation of the present pattern: colder to much colder than normal temperatures with occasional snow, little, if any, rain or freezing rain. And don’t forget the occasional strong outflow winds.

1 thought on “Wind and cold, calm and colder

  1. Jim,

    I always enjoy your meteorological articles. Here, I find it very fascinating how the temperatures in our Southeast communities coincide with those of such notably colder locations in our State’s colder regions. These are things that I would not normally notice and its nice that you bring those to our attention. You enthusiasm for all things meteorological inspires us to take note of the wonder around us. Thank you.

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