Winter Temperature Variance

I'll present this more or less without comment, as I'm feeling a bit under the weather this weekend (no pun intended); but I thought it would be interesting to examine the long-term changes in variance of temperature during winter in Fairbanks.  As we've noted before, there were some remarkable extremes in the 1930s; so has there been a long-term decrease in temperature variance?

The answer is yes.  The chart below shows the November-March standard deviation of daily, weekly, and 30-day mean temperature anomalies, with the anomalies calculated relative to contemporary normals (which have warmed substantially over time).  The variance has decreased at a similar percentage rate for each time scale from daily through 30-day mean temperatures.  We can conclude that the modern winter climate of Fairbanks has somewhat less variability of temperature than in earlier decades prior to about 1980.

What does the decreasing variance look like in practice?  The charts below show daily temperature anomalies for 1950-51, which had daily and 30-day variance very close to the 1930-1959 averages, and for 1993-94, which was very similar to the 1985-2014 average.  The decrease in variance is about 10% on both time scales, which is small but arguably just about perceptible on the charts.

The winter with the highest combined daily and 30-day variance was 1980, and that with the lowest was 1987 (interestingly the latter coming at the end of a strong El Niño episode).