Warm Nights

The temperature dipped below 50°F this morning at Fairbanks airport, which is the first time since June 23.  The 41 consecutive days at or above 50°F is easily a record for Fairbanks; the previous record was 32 days (ending July 26, 1975; July 1975 was the warmest month in Fairbanks history).  Given that the normal low temperature peaks at only 53°F (on about July 6), the absence of any chill in the air during the past 6 weeks is remarkable.

The chart below shows the daily maximum and minimum temperatures since May 1 compared to the 1981-2010 normals.  While daily high temperatures have more often than not been below normal since mid-May, mostly because of all the cloud and rain, low temperatures have been unusually warm.  The average diurnal range so far this summer (since June 1) is only 17.4°F, which is the second lowest on record; only 2014 - which was similarly wet - had a smaller mean diurnal range through this date.

The reduced diurnal range this summer is consistent with the long-term trend, as summer daily low temperatures have experienced 3 times as much warming as summer daily high temperatures in the past 85 years in Fairbanks.  However, the chart below shows that most of the warming in overnight minima seems to have occurred between about 1955 and 1975; this preceded the 1976 PDO shift, so we can't attribute the change to the PDO.  Furthermore, precipitation did not increase concurrently with nighttime temperatures, and in fact the long-term trend in summer precipitation is slightly negative, so increased cloudiness may not be a contributing factor.  A more likely explanation may be population growth and urbanization, which was rapid from the 1950s onward.

It would be interesting to look into these trends a bit more with the help of data from other stations and also with upper-air data from Fairbanks; I'll plan to take this up in a subsequent post.  For now, here's a related post from 3 years ago that I had all but forgotten about until now.