Not Much Cooling

According to long-term normals, temperatures at this time of year are "normally" dropping like a rock in interior Alaska, as net infrared radiation loss takes a heavy toll.  The peak climatological rate of temperature drop in Fairbanks occurs on October 14 (6.2°F per week).  However, in the past 3 weeks the temperature hasn't dropped at all, as the circulation pattern has switched from unusual cold to unusual warmth.  Fairbanks reached 50°F yesterday, which is now well above the normal high of 36°F.  [But recall that I indicated on September 18 that it was unlikely that 50°F wouldn't be reached again.  If it hadn't, it would have broken a record.]

Looking at the last 10 days of September and the first 10 days of October this year, the latter period was actually warmer (35.2°F vs 33.7°F).  This is not too uncommon, having occurred 11 previous times since 1930, but prior to 1990 it only occurred 5 times in 6 decades.  In the 24 years from 1992-present, it has occurred 7 times.

Another way of looking at this change is that from 1930-1991, October 1-10 was colder than September 21-30 by 6.5°F on average.  However, from 1992-2015, the latter period was only 4.2°F colder on average.  So we could say the rate of cooling has diminished by over a third in the 3 weeks surrounding October 1.

Warm conditions notwithstanding, ice formation is now evident on the Yukon River at Beaver and Tanana:

No ice is yet visible on the Tanana at Nenana, however.