Tornado F-Scale Trends
The Storm Prediction Center (SPC) has a tornado mapping program called Severe Plot.
The data archive with this program extends from 1950 through 2018.
I do not know when the data after 2018 will be added to Severe Plot by the SPC.
Remember that the original F-Scale system was replaced with the EF-Scale. The two scales are equivalent, for example an older F-2 tornado, is considered to be the equivalent of the newer EF-2 scale tornado for intensity and damage. I will refer to all tornadoes in the archive as F-Scale tornadoes.
Using this data archive, I put the U.S. data into five-year totals working backward from 2018.
The frequencies of each F-Scale F-0 thru F-5 was totaled (see the table just below here) and graphed (found below the table) to determine if there were any trends in the frequencies of different F-Scale intensities of tornadoes in the U.S.
Table: U.S. Tornadoes by F-Scales in 5-year totals