Surface temperatures have cooled into the -40's at a number of northern interior locations in the past 24 hours or so. Some of the colder observations so far are: Fort Yukon SNOTEL (-50 °F), Bettles SNOTEL (-49 °F), Chalkyitsik RAWS (-47 °F), Arctic Village (-45 °F), Bettles ASOS (-42 °F), and just in the last hour, Eagle airport (-41 °F).
Yesterday's sub-minus 40° reading at Bettles was the first of the season there, and comes one day after the length of daylight (sunrise to sunset) dropped below 2 hours. The day length will remain less than 2 hours until December 28. During this 15-day window each year, Bettles sees -40 °F or lower slightly more often than not; so today's temperatures, despite being well below normal, are not particularly unusual.
Today's FAA webcam images from Bettles, taken a short while after solar noon, showed the half-light of a late December day; despite mostly clear skies, a few high clouds in the south prevented sunshine from reaching the village.