The "Second Season" - Does The Tennessee Valley Have Two Tornado Seasons?
Here in the Tennessee Valley, we're certainly no stranger to severe weather and tornadoes - indeed, from March to May, many of us are constantly vigilant regarding storms and severe weather, as many of the most impactful systems come during this timeframe. However, some of us may remember some equally memorable events that happened in November, December, and other winter months. Some chalk it up to abnormalities in the jet stream, but there exists a lesser-publicized "second season" for severe weather that is certainly no fluke, and indeed can be just as impactful as springtime weather!
One factor in maintaining severe weather through late portions of the year is the cycle of the La Nina/El Nino. Here in the Valley, the correlation is not a necessarily strong one in terms of sheer tornado count, though if lesser frequency, higher octane systems do move through, they sometimes do indeed have the possibility of being higher impact with these more robust systems that can form during La Nina.
For reference, in La Nina patterns, cold equatorial waters in the Pacific push the jet stream northward - high pressure is typically situated near Alaska, and This tends to lead to more variable and sharp jet stream patterns in the CONUS, which is a crucial ingredient for severe weather. Due to the orientation of these systems, they pull warm, moist air from the year-round fairly robust atmosphere of the gulf of Mexico, leading to those muggy warm days, highly conducive to severe weather. These patterns can form with any ENSO cycle, La Nina or not. One can point to many various significant severe weather days that have happened during both patterns!
Nevertheless, looking closer into the region, we can see that it may be more appropriate to say that we have an "off-season", not two "severe" seasons - everyone is familiar with the springtime, but starting in October, a notable uptrend in tornado activity begins, peaking in November and to a lesser extent staying active through the mid to late winter months leading into what most of us consider the typical tornado season. Indeed, October through May could be considered the timeframe of severe weather here. All said, it is dangerous to think the winter months are shielded from the effects of severe weather - December 10, 2021 was one of the most robust severe weather outbreaks in recent memory, and many of us likely remember the impacts Tennessee felt during the substantial and widespread Super Tuesday tornado outbreak of February 2008.
It's prudent to ALWAYS keep in mind these helpful severe weather tips due to this fact - with our proximity to warm, moist air from the Gulf and our downwind position from systems being ejected eastward, we are in a crucial spot for more than half the year of severe weather development. We'll be right there with you for every day of every month of every year, winter or spring - it's what we do. Stay safe out there!