January 70 degree days used to be much more common in the US. There were spikes around 1910 and 1950. In January 1950, almost one day out of eight in the US reached 70F.
The areal coverage of 70 degree days also peaked around 1910 and 1950. In January 1950, almost half of the US reached 70F.
On January 25, 1950 about half of the US was over 60F, and most of the rest was below 0F. Temperatures ranged from -45F (-43C) at Glasgow, Montana to 90F (32C) at Rio Grande, Texas and Greenville, Mississippi.
The US experienced a 135 degree spread across the US on the same day. Experts say that a two degree temperature change would kill us all. New Mexico experienced a 79 degree spread that day.
In January 1906, 70% of US stations reached 60F.
It may have been even warmer, when George Washington was president.