The US has had some very hot July 21st’s. July 21st, 1901 – the average afternoon temperature around the US was 95 degrees, and the Chicago area was 110 degrees.
July 21, 1930 was the hottest day on record in Washington DC (106 degrees) and Delaware (110 degrees.)
July 21, 1934 was the hottest day on record in Ohio (113 degrees.)
July 21, 1936 was very hot in the western US, but relatively mild in the east.