Climate Watch
By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks
There has not been a lot of cold weather so far this winter in western Alaska. Through January 9, Nome has had only 16 days with the low temperature of 0°F or lower, while over the last 50 years the average to this point in the season is 27 days and last winter there were already 43 days.
Unalakleet is not much different, with 18 days at or below 0°F. Even if the remainder of the winter has an above normal number of days below 0F, it’s very likely (but not certain) that Nome will finish with fewer “cold days” for the winter of 2022-23 than we might have expected.
Over the past 115 years there has been a modest but significant decrease in the number of days with low temperatures at or below zero. Prior to 1920 Nome could expect more than 84 days at or below zero, and that’s now down to 73 days, or a trend of about one fewer day per decade. This is not a rapid decrease, but it adds up over time.
Nome has temperature observations for such a long time period, so we extract other kinds of information that might be useful. For instance, we can ask what the chances are that the number of cold days exceeds specific thresholds that might influence important decisions for households and businesses, for example, how much heating oil to purchase. So, what are the chances that Nome will have three months of sub-zero weather? By taking into account the trend, we find that 100 years ago chances were about 40 percent (two winters in five), nowadays the chances are down to about 12 percent (or one winter in nine). Conversely, what are the chances of having less than two months of sub-zero weather? Nowadays it’s almost 25 percent (one winter in four), a dramatic increase from early last century, when chances were only about 6 percent (one winter in 17).
This is an example of how a comparatively small change in the average can hide large chances in the extremes, but often the extremes, are the most important for real-world decisions.