@RodneyS
So... I downloaded some ERA5 Reanalysis data, 80 years worth from 1945-2024, found the average temperatures and then found the change in average temperature between the 2 40 year periods. I then plotted it and these are the results for both days. There's definitely something happening around our part of the country and north on the 13th... what exactly, I don't know.
https://imgur.com/a/yuUYC5l