The arrival of December marks the beginning of climatological winter (astronomical/calendrical winter begins Deceber 21st this year). We in the USA have seen some cold winters recently, especially in the northern midsection of the country.
I was looking at temperature trends in the different climate divisions of the U.S., particularly trends in winter temperature since 1970 (basically the last 50 years).
Red dots mark regions which are warming up, blue dots regions which have been cooling down. There aren’t any blue dots; the whole country has warmed up, although the trend has been slight in the western USA (and not everywhere statistically significant). We can get a better picture of the differences between different regions, by plotting not the warming rate itself, but its difference from average. Now, red dots are regions warming faster than average, blue dots regions warming more slowly than average:
The strongest warming was in the northeast and the northern midwest, the weakest in the northwest.
I also decided to look at short-term “trends.” They aren’t really trends (nowhere near statistical significance) but do tell us about more short-term fluctuations. So I estimated “trends” over a mere 20 years (since the year 2000) and found this:
Now we see actual cooling in the upper midwest, along with warming in the southeast (I’ll emphasize that these are fluctuations, we can’t call them actual trends). I even estimated “trends” over the last decade, since 2010:
Now we see no sign of cooling in the upper midwest, but very strong warming in the southeast.
Perhaps it’s because the upper-midwest cooling happened from the 2000s to the 2010s, while the southeastern warming was mostly during the 2010s. So, I looked at the difference between the average temperature during the 2000s (2000 through 2009) and during the 2010s (2010 through 2019):
And now we get to the crazy idea behind this post: perhaps this pattern (the difference from the 2000s to the 2010s) is really an imprint of an increased tendency toward incursions of the “polar vortex.” I say that because when I’ve seen stories about the polar vortex over the last several years, they seem concentrated on that region of the upper midwest.
It’s only speculation, and very speculative speculation at that. But it’s interesting…
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