While spring has the most notorious reputation for severe thunderstorms and destructive tornadoes, the fall months often bring an uptick in severe weather as the transition from summer to winter takes place.
The Gulf Coast region, where temperatures and humidity typically remain higher than most of the U.S., can experience a secondary peak of tornadoes during the fall. Sometimes, fall twisters can even spread northward into parts of the Midwest. The general tornado risk area in October is shown below.
The fall is when the jet stream begins its southward migration toward the southern U.S. As it does so, it strengthens as the temperature contrast between cold air to the north and warm air to the south becomes more pronounced.
A stronger jet stream can fuel severe weather, adding the spin and energy needed in the atmosphere for thunderstorms to grow and intensify, possibly leading to the formation of tornadoes.
Severe weather in the fall is often found where there’s a southward dip in the jet stream – called a trough – or a cold front moving through a region.
The map below shows that the tornado risk actually increases in November across the lower Mississippi Valley and into parts of the Southeast when compared to October. Tornadoes are also still possible farther north into parts of the Midwest in November.
However, the main risk for tornadoes retreats back toward the northern Gulf Coast states by December. That’s because most of the warmth and moisture is limited to that region as winter sets in across the U.S.
Any late-season tropical activity can also provide an uptick in severe weather along the Gulf Coast in November and December.