In Kansas, most people think of one time of year for severe weather season... spring. In many respects that is correct. The spring storm season has some of the most violent storms that Kansas has to offer. If you think about the shear number of severe thunderstorms that we see in the region, that stands to reason. The more storms that you see, the likelihood that we will experience damaging wind, hail and the occasional tornado will go up.
The driving force for this is the jet stream. Each spring the jet stream makes the yearly migration to the north. When this happens, we a sudden spike in the ingredients that we need for thunderstorm development. The temperatures get warmer, the moisture content in the air goes up and we get upper level support from the jet stream which allows the frequency and strength of thunderstorms to go up. Cold fronts tend to be more frequent and stronger as well, which adds to the violent nature of some of these storms.
Think of the Fall as our secondary severe weather season. We still have the heat and humidity that we need for severe weather, but we are re-introducing the jet stream along with a seemingly sudden surge of cold fronts to the mix. As the days get shorter and become cooler, the jet stream will begin to once again move to the south and bring the upper-level dynamics that seemed to be missing for these storms during a good portion of July and August.
Keep in mind that severe weather can happen at any point during the course of a year. Over the course of time, Kansas has had a tornado in all twelve months of the calendar year.