Monday, October 12, 2015

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.


  1. A question please...what controls temperature loss via IR radiation at the surface? Perhaps there's a scaling of options like overlying temps, cloud cover, or ?


    1. Gary, The three main components are the temperature of the surface (a warmer surface radiates much faster), cloud characteristics (coverage, thickness, temperature), and water vapor concentration above the surface. Clouds and water vapor aloft radiate down to the surface and thus slow or reverse the surface loss.

      I'll do a post on the estimated radiation budget for Fairbanks.

    2. Thank you in advance Richard for any further insight. Learning can be fun.

      I've assumed predictive models of future weather and climate assess various factors, but have never explored the suite of components and their contribution.


  2. Clouds and atmospheric gases are also emit longwave radiation that is absorbed by the ground. Meet and greet at Luton airport