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.
Some background discussion on Urban heat islands, thermal inertia, and albedo:ReplyDelete
My comments from 8/13 still apply to the airport-driven heat island surrounding the weather obs station. The surface water temp in the airport float pond was +68F today.ReplyDelete
That heat source, a high pond water level/volume from the recent rains, and nearby river levels almost bank full surely has a delayed warming effect on surface air temperature at night if the winds are right.
Excellent comments, Gary. The float pond is a new consideration for me; I wonder if that was constructed at the same time as the airport.Delete
Yes they accessed the gravel via draglines and other equipment to raise the operating surfaces above the flood plane during construction...I assume per some Q** predicted flood level. It opened in 1951 and I believe somewhere here is a history of the various obs locations.Delete
The main floatplane pond has been lengthened and deepened since inception, while similar ponds to the south have been filled to discourage waterfowl.
Look at an aerial shot (https://en.wikipedia.org/wiki/Fairbanks_International_Airport) or Google Earth to see the urbanization effect due to dark surfaces (paved areas, cut vegetation, and structures) plus the ponds and nearby rivers.
All that development affects surface temperature and wind at the obs site located between the southerly ends of the two main runways (to the left on the pic in the link above).