My investigations suggest that the strongest influence on extreme heat is the increase in average temperature during summer; the shape of the distribution can change, and that has an effect, but change in the average value dominates. So I decided to look at how summertime heat has changed in each climate division of the conterminous USA (i.e. the “lower 48 states”), according to the data for high temperature from NOAA.
For each division, I fit a smooth curve (lowess smooth), then estimated the “summer warming” as the difference between the smoothed values now (i.e. in 2021) and at the start (i.e. in 1895). Some of them show considerable warming, in fact the northeast corner of Utah has warmed by a whopping 6.05°F:
Although most climate divisions show summer warming, not all of them do; in fact in Alabama there’s a division which shows cooling by -2.39°F:
Whichever divisions in the USA have warmed by the most, are most at risk for never-before-seen extreme heat. And here they are as red dots (bigger dots, bigger risk), with blue dots indication regions which have shown net summer cooling (rather than heating) since 1895:
Two regions stand out as being at greatest risk. First is the entire U.S. west, westward of longitude 100°W. Second is the northeast coast, northward of Washington D.C.
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Open Mind 
Good work. I’ve been doing this type of investigation for many years. The warming and cooling patterns I’ve discovered have surprised me. Here is my collection of articles:
https://datablends.us/climate-change-quantified/
Anyone done something like this for Australia ?
Perhaps interesting to speculate as to whether the color and/or size of the red & blue dots are related to acceptance or resistance to the reality of climate change or government action to deal with it.
Hmmmm. Increase in hot air downwind of Washington, D.C.
Whooda thunk?
Very interesting. Shows that climate change has to be looked at specifically and broad brush assertions are risky to be false.
The potential flaw here is that it assumes you can extrapolate past change into the future. To me it seems likely that weather patterns are going to change more drastically as the Arctic heats up, and then anything can happen.
I hadn’t expected that rise in the NE at all, because precipitation has increased significantly there over the past decade or so, and you’d think that would imply some cooling. But then… for each 1 deg C increase in atmospheric temps, the air can hold roughly 7% more moisture. So that makes sense.
Very happy for your return to Climate Change blogging Tamino.
Your skills and wit have been missed by many of us.
I note on one of your recent posts you state.
I think I understand your retirence to comment beyond what you can support with pure staticascal analyse
Dr Jason Box has some interesting comments on the effect of the jet stream in this recent interview on the Arctic that also supports more is going on than underlying Global Warming .
It frightens me that by the time indicators in the climate system attain statistical significance the earth will have already irreversibly passed tipping point/s.