The 2021 December 10-11 outbreak of deadly tornadoes in the Mississippi Valley and the Ohio Valley of the US raised questions about changes of tornadoes. The figure below of annual US strong tornado counts includes the trend for the period of record as well as for a briefer period. The period of record trend indicates a large decrease while the briefer period indicates a small increase.
Notes
NOAA NWS Storm Prediction Center, "Warning Coordination Meteorologist's Page," US tornado data accessed February 24, 2021, https://www.spc.noaa.gov/wcm/#data