An upward trend in Ontario tornado frequency (about 1.6 tornadoes/decade with the statistically significant
level at least at 95%) is identified using three independent approaches. The first method is the conventional linear
regression method that had no disturbance to the original tornado time series. The second approach is to employ the
Mann-Kendall test with consideration of removing a lag one autoregressive process. The trend is further firmed up using
the Monte Carlo simulation. The robustness of the detected tornado frequency trend presented in this work offers an
example for tornado frequency trend analysis over other regions of the world. It is shown in this study that the Ontario
tornado frequency is linked to ENSO (El Niño/Southern Oscillation) signals with a statistically significant level at 99%.