NOAA has an annual tornado report that contains the graph here. The graphs suggests an increase.
In contrast to the previous four years, tornado activity across the U.S. during 2017 was above average. During January-September there were 1,262 confirmed tornadoes with 144 preliminary tornado reports still pending confirmation for October-December. This brings the preliminary tornado count to 1,406 with the final count expected to be slightly lower. The 1991-2010 annual average number of tornadoes for the U.S. is 1,253.
The page includes a map of the locations of tornadoes for 2017, a drop down menu for years dating back to 2006, and as monthly menu. You can download tornado data from NOAA’s Storm Events Database.
