Tornado Outbreak Looms In Lower Mississippi Valley

NOAA's Storm Prediction Center is warning of a possible
tornado outbreak on Tuesday, especially in areas of this
map that are shaded in orange and red. 

 We normally think of big tornado outbreaks and springtime creatures, but there is a "second season" for tornadoes in the late all and winter. 

Tornado outbreaks this time of year are not nearly as common as they are in the spring.  But they do happen. And, using last December's extreme and horrible tornado outbreaks as an example, winter tornado outbreaks might be getting worse with climate change. 

Which leads me to Tuesday's forecast for places like parts of Louisiana, Arkansas, Mississippi and Tennessee. 

There's growing confidence that several tornadoes might spin up in this region, and some of them might be quite strong and long-lasting. 

Forecasting tornado outbreaks, even just a day ahead of the event, can be tricky. Sometimes, all the ingredients are there for a bunch of tornadoes and nothing much happens. Or, only a few of the ingredients for tornadoes are there, but all hell breaks loose.

And sometimes, all the ingredients are there and sure enough, chaos reigns.

In this case, the factors that can create a tornado outbreak seem to be coming together. A storm system coming in from the west will pull lots of very wet air from over the Gulf of Mexico into the target region. 

Meanwhile, the storm will begin to cool the upper atmosphere over the lower Mississippi Valley, which would increase instability and encourage thunderstorms 

Additionally, strong winds will scream high overhead. The winds will change direction with height, which encourages supercell thunderstorms that spin. These spinning storms can then send tornados across the landscape. 

In the spring time, the sun is stronger, which means the surface can heat up better. That makes the atmosphere all the more unstable to encourage severe weather. That strong sunshine is missing this time of year, but the strength of the parent storm can overcome the lack of a contribution from the sun.

As noted above, there's also the risk that climate change could make late autumn and winter tornado outbreaks worse.

Whether climate change intensifies or not, we will always have the occasion strong winter storm with fierce upper level winds that can trigger tornadoes in the South. 

However, the air coming from the Gulf of Mexico during these episodes is becoming warmer and more humid with time. That wet air just adds fuel to the fire, possibly making tornado episodes worse. 

I would hope this doesn't lead to months like last December. An outbreak of large tornadoes in and around Kentucky killed 80 people and caused $3.9 billion in damage, according to estimates. 

Less than a week later, a large derecho with as many as 120 embedded tornadoes swept the Midwest as far north as Minnesota, which is extremely rare for December. This second storm caused seven deaths and caused nearly $2 billion in damage.

The storm that is expected to cause Tuesday's tornadoes is likely to bring wind and rain to us here in Vermont on Wednesday, but severe weather is not in the cards.  We might face some minor localized flooding if it rains hard enough, and we could also see some scattered power outages caused by the gusty winds that are in the forecast.