Why So Warm on the North Slope?

Courtesy of NCEP/NCAR Reanalysis

Long time reader Trung asked why it has been so warm on the North Slope this summer. The obvious answer would be that the record low sea ice coverage, but that in fact is probably only a small part of the answer. Ice has actually been more persistent in the Chukchi and far western Beaufort Sea than it has been in a few years, though what's left is rapidly melting now. More important has been the persistent trough aloft centered along about 170W longitude, the same feature responsible for the copious rains over much of western Alaska and the quasi-drought in the Interior. This can be seen in graphic to the right, which shows the mean wind direction (arrows) and speeds (color) at 700 mb (about 3000 meters above the ground) for July 1 through August 20 (speed units are meters per second). South winds blowing across the Brooks Range warm and dry as they descend onto the northern plain in a classic "chinook" effect. Barrow has had 15 days with a daily high temperature above 60F, which ties with 1989 and 1936 for the most such days. It is possible that  a new record could be set in the next ten days or so.