The 1930’s was by far the hottest decade in the US, with every state running hot for the entire decade. Notable heatwaves occurred in 1901, 1913, 1931, 1932, 1933, 1934, 1935, 1936, 1954, 1961, 1976, 1980, 1988 and 2011. The coolest summers were 1915 and 1993. No states were abnormally hot during the summer of 2016.
1993 was cool because of the eruption of Mt. Pinatubo, and there must have been something similar in 1915 – which was cool across the entire US.
Climatological Data for the United States by Sections – United States. Weather Bureau – Google Books
Mt. Lassen did erupt in 1915, but it seems unlikely this was big enough to cool down the entire US.
Eruptions of Lassen Peak, California, 1914 to 1917 — A Centennial Commemoration | Science Features
