In a recent post I showed that in June the northwest had its most extremely hot month on record.



To compute how extremely hot each month was, I took the difference between the month’s temperature and the average for that month throughout the year, returning temperature anomaly. Then I divided the anomaly by the standard deviation for that month to compensate for the fact that winter months show more variation naturally — a large departure from average isn’t so unusual in winter as it is in summer, so such a departure isn’t really so “extreme.” For the northwest, June was the most extreme out of all 1,446 months on record (using data from NOAA).

It’s easy to imagine my being accused of “cherry-picking” for choosing the northwest, now. After all, we just had an extreme heat wave there — what a time and place to pick! It made me wonder, what about looking at all of the U.S. states? I could almost hear the protests that “Oh yeah? Well state (insert state here) had its most extremely hot month way back in (insert year here).”

So I did exactly that. For each of the 48 states in the conterminous U.S. I computed which month was the most extremely hot, after computing anomaly (to allow for the seasonal cycle) and scaling by the month’s standard deviation (to allow for the greater natural variation in winter months).

Here’s a plot of how many states had their most extremely hot month in each year since 1895:

Clearly there have been some years that brought extreme heat. In fact, back in 1961 no fewer than six states had their most extremely hotter-than-normal month. But 2012 topped even that, with seven states reaching the pinnacle of hotter-than-usual.

More noteworthy is the fact that even though most years no state reached its peak, every year of the 2010s at least one state did. So I also tallied how many states had their most extremely hot month by decade. The result is quite telling:

In 2nd place is the decade of the 1960s, with seven states experiencing their most extremely hotter-than-usual month. But in 1st place, by a huge margin, is the 2010s. This decade we’ve already seen eighteen states reach the extreme. Truly, here in the U.S. the 2010s have beaten all those other decades by a wide margin.

And the decade of the 2010s isn’t even over yet. It’s barely more than half over.

UPDATE:

A reader wondered what it would look like to compute the most extremely colder-than-usual month for each state. Here it is, by year:

And here, by decade: