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'Second' tornado season can cause problems in December

Many people let their guard down in December thinking it's not the season for severe weather and tornadoes, but in reality it's all about the atmospheric conditions.

While spring has the most notorious reputation for severe thunderstorms and destructive tornadoes, the fall months often bring an uptick in severe weather as we transition from summer to winter.

The Gulf Coast region, where temperatures and humidity typically remain higher than most of the United States, can experience a secondary peak of tornadoes during the fall. Sometimes, fall tornadic activity can even spread northward into the Midwest and mid-Atlantic. The general tornado risk area in October is shown below.

October tornado probability

(FOX Weather)

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 be fuel for severe weather, adding the spin and energy needed in the atmosphere for thunderstorms to grow and intensify, possibly leading to the formation of tornadoes. 

HOW ARE TORNADOES RATED? THE ENHANCED FUJITA SCALE EXPLAINED

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 other parts of the Deep South when compared to October. Tornadoes are also still possible farther north into parts of the Midwest and mid-Atlantic in November.

November tornado probability

(FOX Weather)

However, the main risk for tornadoes retreats back toward the South 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. 

HERE'S WHY THE ATLANTIC HURRICANE SEASON RUNS FROM JUNE TO NOVEMBER

December tornado probability

(FOX Weather)