Thoughts & observations

Number of U.S. counties or county equivalents with each climate classification:

Dominant climate classification by region

Dominant climate classification for each state, district or territory

Anchor city of largest metropolitan statistical area with each classification

My observations

• Even when using the 0°C isotherm rather than a -3°C isotherm (which is commonly accepted) for distinguishing between temperate (C) & continental (D) climates, Cfa climates still encompass a plurality of county climate classifications in the United States. With climate change, the proportion of Cfa to Dfa climates will probably continue to grow
• I went through and calculated the Köppen classification by hand for every county in the country. When comparing my results to the results online, our classifications generally agreed with one another, with the exception of the C vs. D climates as mentioned above. However, online classifications for areas on the western end of the Great Plains, such as the western parts of Texas and Oklahoma, tended to miscategorize Cfa climates as BSk instead. srsly do better
• Didn't expect to see many dry-winter (Cw, Dw) climates in the US, but there were a few in the Midwestern states. There might even be more dry-winter climates in smaller towns, since I only calculated climates for county seats.
• Climate-Data.org seems to report lower temperatures on average compared to other sources. I used their data for many counties in the Midwest & Northeast, so there might be even more Cfa counties (and, therefore, less Dfa counties) than shown on the map