If residents of central Alaska have a sense that this summer has seen unusually steady temperatures, without extremes of either cold or heat, they are correct. In fact, according to daily Fairbanks data, the standard deviation of daily mean temperatures since June 1st is the lowest on record. Since at least 1930, there's never been a summer with less variability in daily temperatures through August 12.
The slight downward trend over the 90 years of data is not statistically significant, but the trend since 1990 actually is marginally significant at a 95% confidence level.
This summer's daily temperature variance is also the lowest on record - and by a larger margin - at McGrath, and it's the second lowest on record at Bettles.
Here are daily temperatures since May 1 in comparison to normal for the time of year in Fairbanks. Lots of small deviations from normal.
What explanation might we propose for this summer's unusually steady conditions? It would be interesting to look at seasonal climate drivers that tend to impart low variance, but for now the answer is rather simplistic: the general weather pattern has precluded the strong ridge/trough waves in the atmosphere that create larger swings in temperature from day to day and week to week. In particular, it's the ridges that have been missing, as 500mb heights have been lower than normal over eastern and/or southern Alaska. This seems to have been a relatively stable configuration, with few significant perturbations to bring much warmer air to Alaska's interior.
Here are 500mb anomaly maps from June, July, and August so far:
As for the downward trend in the past 30 years, it may well be the reduced frequency on the cold side of the climate distribution that explains the reduction in summer temperature variability. In other words, as the Arctic has warmed far faster than the rest of the Northern Hemisphere in recent decades, air from the north will have warmed much more than air from the south. It would be useful to look at this in more detail when time permits.
Update August 14:
It turns out there's no meaningful correlation between the mean and the variance of summer daily temperatures (after removing the long-term trend from the mean), so it seems we can't say that cool summer weather patterns (for Fairbanks) are inherently more stable.