Thursday, September 16, 2010
Here's a plot of daily high and low temperatures for three different locations in the Fairbanks area since the big ridge build in over the weekend. With clear skies and no wind to speak of, every night radiationally cooled air pools in the valleys, and each afternoon the sunshine is still strong enough to mix out the morning inversion. As a result, valley bottom locations have big diurnal ranges (46 degrees Wednesday at Goldstream Valley Bottom), while the high elevation sites have much smaller ranges (13 degrees Wednesday at Keystone Ridge). So, it's not there is so much heating from the sun that it raises the temperature by 40 some degrees; rather, the heating is enough to mix down the warm air that is lying just above the surface. The overall heating is reflected in the high elevation diurnal ranges: 15 degrees or less with 100 percent of the 13 hours of possible sunshine.