The past week has seen some unpleasant wind chill in many of the typical cold spots of western and Arctic Alaska. The conditions haven't been particularly extreme by historical standards, but this serves as an opportunity to look at what is unusual or extreme according to local climatology.
Let's start with Bethel, where strong cold outflow from the interior quite often brings notable wind chill. On Monday morning the temperature was -15°F with a sustained northeast wind of 35mph (see below), which is good for a wind chill of -47°F. This is just a few degrees shy of what's typical for the lowest wind chill of the winter (around -50°F). The average wind chill for the duration of Monday in Bethel was -43°F, and a day like this has occurred in about two-thirds of winters in recent decades (although not at all from winters 2012/13 through 2015/16).
Based on the 1991-2020 history, a wind chill of -40° occurs about 5% of the time in Bethel in December through February, and the wind chill is below -50°F about 1% of the time on average. For its latitude and (sea level) elevation, Bethel is remarkably prone to very low wind chill.
The Arctic coast had similar wind chill yesterday, although there it was much less unusual. Barter Island measured -55°F for wind chill in the afternoon on a stiff easterly breeze:
Up at Barter Island, the winter's worst wind chill is typically a full 10°F lower, at -63°F, based on the 1991-2020 history. Remarkably, since 1991 the location has spent about 2% of the time in January with a wind chill below -60°F, although the majority of this time occurred in just a few severe and prolonged events; some winters do not see a wind chill of -60°F.
To summarize the low wind chill climate of the exposed west and north coast of Alaska, the figures below show the 10% and 1% levels of hourly wind chill for Bethel, Nome, Kotzebue, Utqiaġvik, and Barter Island. The 10% level might be considered a threshold of "unusual" low wind chill, and occurs nearly every winter, whereas the 1% level represents a more extreme event that occurs in less than half of winters.
It's interesting to note that Nome is relatively sheltered from the northerly winds that would otherwise bring the lowest wind chill, and so it has easily the least extreme wind chill climate of these locations. Also, the prolonged winter of the Arctic coast is evident, as low wind chill hangs on into March and even April for Utqiaġvik and Barter Island. Readers will no doubt spot other interesting aspects - feel free to leave a comment.