Wind Trends

In last week's post, I noted that Alaska's 10-year running mean precipitation is at a record high, reflecting the fact that the state's climate has become generally wetter in recent decades.  It's common knowledge that temperatures have also increased on a timescale of several decades, especially in the Arctic.  But what about wind?  Are there any notable multi-decadal trends in wind speed for Alaska?

The question of climate trends is not as straightforward for wind, because there is no good long-term "ground truth" data for wind speeds; measurement practices have changed too much over the years.  We have to rely on retrospective estimates from a model, which in my case means the ERA5 reanalysis from the European modeling center.  So take the following results with a pinch of salt.

First we can observe that last year was apparently the windiest year in many decades for Alaska as a whole (according to ERA5); and it was particularly windy over western regions:

This wasn't just caused by one windy month; 6 of 12 months saw statewide winds at least 5% above normal, and January and August were particularly windy.  Only one month - September - was notably calm compared to normal.

Does this reflect a long-term trend towards greater winds?  No: ERA5 data indicates no significant trend over Alaska's land area, and if anything it suggests an absence of windy years in the last 20-30 years.  2024 was quite anomalous compared to the previous couple of decades:

Here's a look at the 75-year change in annual mean wind speed, using a linear trend, and including 2024:

The results in the complex terrain of southern Alaska are highly variable and probably not representative of the actual trends at populated valley-level locations.  (The ~30km horizontal resolution of the ERA5 data is far too coarse to handle complex terrain.)  There's a marginal hint of decreasing wind speeds across parts of the interior, but clearly the model shows increased wind speed across the near-coastal waters of the Bering Sea as well as more widely in the Arctic Ocean.

The seasonal breakdown of the trends shows a few interesting results - see below.  First, the largest percent increase in wind for the Bering, Chukchi, and Beaufort Seas is found in winter, although the Arctic waters have also become more windy in summer and autumn, if the model is to be believed.  The winter trend of increasing wind is also evident across the western land area and the northern interior.  However, it seems that the North Slope and the northern interior have become less windy in autumn, and there is a distinct trend toward less windy summers in the southwestern interior and Bristol Bay region.

The rising wind trends over the Arctic and Bering waters may have more than one cause.  First, there seems to be a trend toward greater storminess over the Bering Sea in winter; the two maps below show the multi-decadal difference of 500mb heights (top) and MSLP (bottom) for 1950-1990 versus 1991-2024.  This is consistent with the December-February wind increase extending inland across northwestern Alaska and the northern interior.

But the general warming trend in the Arctic is also a direct cause of rising wind speeds across the Arctic waters, because the surface-based temperature inversion has weakened, allowing more atmospheric momentum to mix down to the surface.  This effect is pronounced in autumn, when sea ice loss has been dramatic (see the Sep-Nov map above).  Here's a paper from last year on this topic:

https://www.nature.com/articles/s43247-024-01428-1

As for the summer wind decrease in southwestern Alaska, this is probably related to increasing high pressure and fair-weather "ridging" over the Bering Sea at that time of year.  In contrast, the Arctic Ocean seems to have become more stormy, especially in the Eastern Hemisphere.

So far this year, we've seen a very windy January - one of the windiest on record statewide (2024 was the windiest) - but February and March were somewhat less windy than normal.  It will be interesting to see if we have another windy summer, following last summer's record high wind statewide.  I see some reasons to believe the high-latitude summer patterns could indeed be similar to last summer - but more on that another time.

Active Weather

The weather pattern has been very energetic and changeable across Alaska in recent days, leading to sharp cold in some areas, and wind and storm damage in others.

Coastal erosion and damage occurred down in Homer over the weekend, and far to the northwest Point Hope is without power today, owing to high wind.  Winds gusted to 68mph in Point Hope yesterday, and 93mph at nearby Cape Lisburne.  Today the high winds spread across the North Slope, with Utqiaġvik gusting to 62mph and temperatures rising above freezing.

Here's this morning's 3am MSLP analysis, courtesy of Environment Canada:

Several things can be noted here: the axis of high pressure across the southern interior, associated with cold weather at the surface; the strong pressure gradient across northwestern Alaska, producing the high winds; and the extraordinarily deep low pressure system to the west of Seattle, causing severe wind damage in Washington last night.

The cold yesterday morning was notable across the interior: -40° was reached on the Yukon Flats at Beaver, and Chicken saw -42°F.  Fairbanks reached -29°F at the airport, the coldest this early since 2020 - and we have to look back to 2011 to find colder conditions this early in the season.  The Salcha RAWS reached -37°F, the coldest this early since 2011.

Summer Wind

Here's a bit of follow-up on the remarkably windy summer that occurred over parts of western Alaska.  According to ERA5 data, the June-August average 10m wind speed was the highest since at least 1940 for areas shaded in red below:

The east end of Norton Sound was perhaps the epicenter of the anomaly, including communities like Shaktoolik and Unalakleet.

To confirm that this isn't just a model artifact, here's the history of June-August wind speed measured at the Unalakleet airport since 1991:

The airport instruments have been classified as an AWOS platform since 1991, so I have some confidence that the wind measurements are relatively consistent since then.

The seasonal mean wind speed of just over 11 mph may not seem like much, and indeed it isn't much compared to winter wind speeds in Unalakleet: the average wind speed is over 15 mph in February.  But it's historically very unusual for the time of year: 8 separate days had a daily mean wind speed over 20 mph, compared to a previous (post-1990) record of 5 days, and over 30 days this summer saw peak sustained winds over 20 mph (normal is 16 days).

Here's a chart of daily average winds compared to a 20-year normal, for an ERA5 grid cell very close to Unalakleet.

Most of the wind action was in July and August, with the early July event standing out dramatically: that was when the pattern suddenly changed to westerly, as we noted at the time:

https://ak-wx.blogspot.com/2024/07/big-pattern-change.html

Ex-Typhoon Ampil

The third major storm in less than a week affected western Alaska yesterday, courtesy of the remnant circulation of Typhoon Ampil.  The low pressure center came in a bit farther north than the previous two storms, but high winds were widespread across the western coastline and hills.

Here's the MSLP analysis from 4pm AKDT yesterday, courtesy of Environment Canada:

The wind gusted to 55 mph in Nome in the early evening, and the peak sustained wind of 41 mph ties the Nome record for August, set back in 1949.  To find a stronger storm in early autumn, we have to look to the first week of September, when 44 mph sustained winds were measured in 1964.  (But instrumentation is different nowadays, so it's not really a fair comparison.  In recent years the most comparable event was August 24, 2012, with 37 mph.)

Here are some of the peak wind gusts around the region yesterday (in mph):

Although this is the 3rd storm in quick succession, it's actually the 4th storm to hit the west coast in the past two weeks (I missed the first one in my previous post).  Here's the MSLP analysis from the afternoon of August 10: this one came in much farther south.

The 14-day precipitation is 2-4 times normal across much of the west and northwest, and the anomaly pattern is extremely similar to the July outcome - except for Southeast, where it's been much drier lately.

Follow-Up

A quick follow-up post on last week's big pressure gradient and associated wind: with ERA5 data now available, the peak MSLP difference between two Alaska land points was 95mb, i.e. not an all-time record, but certainly in the upper tier of these events.

However, I redid the historical calculation for land points from 170°W eastward, i.e. excluding the central and western Aleutians.  The rationale is that last week's Aleutian cyclone was farther east than others that produced extreme pressure differences across the state, and I wanted to see if it might be an all-time record for the more restricted domain.

And the answer is - yes!  The pressure difference of 95mb within Alaska east of 170°W is indeed the greatest back to 1950, based on hourly ERA5 data.  Only two previous events exceeded 92mb across this domain: November 26, 1985, and December 5, 2009.

Here's a revised chart of the annual (cold season) maxima for the smaller domain:

Interestingly there seems to be a slight downward trend in the series, although it's not statistically significant.  Another interesting aspect is the tendency for large positive outliers once every 10-20 years.  Last week's set-up was a rare event.

Most regrettably, the high winds produced by this system led to treacherous conditions high on the Steese Highway last Wednesday, leading to the deaths of two motorists:

https://www.adn.com/alaska-news/2024/01/05/recovery-of-2-found-dead-in-interior-alaska-vehicle-complicated-by-poor-weather-troopers-say/

Conditions were indeed very poor: here's the hourly data from the Eagle Summit SNOTEL site (click to enlarge).  Columns are temperature and wind chill in °F, wind direction, wind speed in mph, and solar radiation (absolute and percent of possible).

I don't have historical data for comparison, and Eagle Summit is notoriously cold and windy, but it's clearly not the kind of weather you want to encounter unprepared.

Kaktovik Wind

Blizzard season is off to an early start in Alaska's capital for that kind of thing: Kaktovik, on Alaska's eastern Arctic coast.  Snow has been flying since Thursday morning, and winds increased to 50 mph yesterday evening (with gusts to 60 mph).  Thanks to reader Mike for bringing this to my attention.

October is rather early for this kind of weather in Kaktovik, and it's been more than 10 years since such high winds were observed in October.  In winter proper it's more common, with more than 5% of days seeing sustained winds over 45 mph in November through February.

Here's the meteorological setup: high pressure over western and central Alaska, and a deep low pressure system over Banks Island (as of 4pm AKST yesterday).  My clumsy annotation shows the direction of the strong pressure gradient, and Barter Island's location is indicated with the red dot: click to enlarge.

Another Kotzebue Blizzard

It's only been 3 weeks since I wrote about back-to-back blizzards in Kotzebue that led to a local disaster declaration (news link courtesy of reader Gary), but another major storm affected the area last weekend.  Remarkably, hurricane-force wind gusts were reported by the airport ASOS, although the observations were missing for several hours, so perhaps the instruments malfunctioned.

By my count, this makes five real blizzards in Kotzebue this winter: November 7, December 10-11, February 21-23, March 4, and March 25.  Each of these had sustained winds above 40mph.  There was also a storm on January 27-28 that briefly met the blizzard criteria (35mph wind and 1/4 mile visibility).

In light of the recurrent storminess in Kotzebue, reader Andy's recent comment about Nome being "inundated with snow in many recent winters" is very interesting and worth a closer look.  Let's have a look at November-March precipitation for the two sites: the charts below show results both from the standard climate observations and from the nearest grid cell in the ERA5 reanalysis.

 

The large wet bias in the ERA5 data is not unexpected in model data, and it's not generally regarded as a problem - the user just has to implement a bias correction.  Much more importantly, the year-to-year correlation between ERA5 and the ground truth data is fairly good back to about the mid-1970s, giving us some confidence in both sources for the last several decades.  (The ERA5 does not use precipitation observations in creating its global gridded estimates.)

Excluding pre-1980 data, there's little trend in Nome winter precipitation, although the two very wet winters of 2017-18 and 2018-19 certainly count as being "inundated".  At Kotzebue, however, there does seem to be a significant trend towards wetter winters in both the ERA5 and ground-truth data, and the absence of a "dry" winter since 2016-17 is notable.

As for the earlier decades, the situation is more uncertain.  The Nome precipitation data doesn't seem to have enough year-to-year variability in the 50s and 60s.  The correlation with ERA5 is poor in the early decades for both sites, although that by itself doesn't invalidate the climate observations, as the ERA5 uncertainties are much greater for that time.  The pre-1970 numbers from Kotzebue are so low that they seem unreasonable at first glance, but if indeed the winter climate was more truly Arctic back then, then perhaps much lower precipitation is plausible.  Utqiaġvik averages less than 2 inches total precipitation in November through March even after becoming much wetter in recent years.

So much for precipitation; but how about high winds (the "blizzard" aspect of the problem)?

We don't have consistent wind measurements across the decades, so I again turned to ERA5 and extracted the hourly wind speed back to 1950 for both sites.  I determined the peak wind speed for each winter (November-March), calculated the median of those numbers, and then found the number of hours each winter that exceeded that "typical winter maximum".  The ERA5 winds are a bit lower than reported by the ASOS instrument of today, and in reality this "typical winter maximum" corresponds to sustained winds of about 40mph in Nome and 50mph in Kotzebue.  Half of all winters see winds of at least this strength at some point.

 

To bolster confidence that ERA5 winds are realistic, I checked the highest values in the history.  The highest ERA5 hourly wind speed for Nome was at 9pm on December 28, 2021, and indeed that day saw a major wind storm that peaked at 8:30pm.  In Kotzebue, the highest ERA5 wind speed in recent decades was at 11pm on February 18, 2006, and the observed wind speed peaked at the very same hour.

It's interesting that both sites have seen an increased frequency of winters with relatively high winds in the past 20 years; there have been few winters without high wind, especially at Kotzebue.

As for the maximum winds each winter, there's a hint of an upward trend in recent year for Nome, with few recent winters on the low side of the distribution, and the change seems a bit more pronounced at Kotzebue - see below.

Finally, looking at the number of days that met the blizzard criteria in the past 25 years (approximately the ASOS era), there's again perhaps just a hint of an increase in Nome, and Kotzebue has had 9 or more blizzard days in 5 of the last 6 winters.

All in all, it does seem that a trend is emerging at Kotzebue, although as usual the year-to-year variability makes it difficult to be sure, and formal significance testing would likely not give a resounding message.  The trends at Nome seem more tentative and uncertain.  Remind me to take another look at this a few years from now...

Wind and Cold

After last week's extreme rainfall in Southeast Alaska, a noteworthy North Pacific storm brought a lengthy episode of strong winds to southwestern parts of the mainland earlier this week.  Here's a surface analysis from 3am Sunday, courtesy of Environment Canada:

Bethel had two unusually windy days on Sunday and Monday - with snow and temperatures down near 0°F to start - and the wind was really howling at the more exposed locations.  For instance, Cape Romanzof (admittedly a very windy place) reported sustained winds around 60-70 mph for a full 24 hours, with gusts of 80 mph.

Our old friend Howard Pass, up in the western Brooks Range, also saw a modest blow as the pressure gradient worked its way north this week.  In characteristic fashion, the temperature dropped as the wind picked up at the pass, and bottomed out at -20°F with 40-45 mph winds.  Nasty, but nowhere near the conditions that have been observed there on some past occasions.

The fact that the strongest winds in western Alaska often seem to prevail from a northerly direction got me thinking about whether there is in fact an inverse correlation between temperature and wind speed in these areas.  In the interior lowlands we would generally expect the opposite in winter: wind brings warmth, but what does the relationship look like on a map?

With the ERA5 reanalysis, we can answer this question with a fair degree of confidence.  The sequence of maps below shows the correlation coefficient of daily mean 2m temperature and daily mean 10m wind speed, by month, from 41 years of data.  Click the images to enlarge.

Interesting features to me are:

- Inverse correlation (cold when windy) in the highest elevations

- Positive correlation (warm when windy) in winter across the interior North Slope, the Kobuk valley, the Yukon Flats, the mid-Tanana valley, and elsewhere in the lower elevations of the west.

- Inverse correlation in summer across western Alaska and the oceans (warmth occurs in conjunction with high pressure and reduced winds)

- Very high positive correlation in the warm half of the year across northwestern Canada and parts of eastern Alaska - but apparently not directly corresponding to elevation.  I'm not sure what to make of this.

If readers have any comments or insight on the patterns, I'd be glad to hear them.