Climate Watch

By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks

With winter weather finally in place across the region, we’re reminded of one of the most important features of our winter climate: wind chill.

Wind chill is an attempt to combine the effect of wind and temperature into a single number, usually as an equivalent temperature in the wind was not blowing.

It’s important to know that wind chill is not a physical quantity but rather is calculated using many assumptions, including typical human response to low temperatures and assumes there is no sunshine offsetting the wind.

With low temperatures, winds make it feel colder because it is constantly moving air away from our body that otherwise would be warmer slightly. And in tundra environments, not only are wind speeds at ground level higher than in the boreal forest, there are also fewer ways to find shelter from the winds.

Wind chill is one of the winter weather elements for which the National Weather Service issues advisories and warnings. For western Alaska, there are three pieces of wind chill advisories and warnings: winds have to be sustained at 15 mph or higher, and the wind chill has to be at least -40°F for an advisory and -60°F for a warning, and both wind speed and wind chill conditions have to persist at least three hours.

In most communities in the region (except in the Bering Strait) it’s actually quite unusual to meet these criteria. With the modern wind chill calculations, Nome Airport has not met the wind chill warning criteria since 2012.

Wind chill advisory criteria occur slightly more often, but even that has been very rare in the past decade. Of course, outside of communities these conditions do occur more frequently, for instance in the Topkok area, as more than a few Iditarod mushers over the years have learned through bitter experience.