Climate change and tornadoes in Tennessee

Scientists are pointing to increasing signs that climate change is altering tornado outbreaks in ways that appear to make them bigger and more damaging, Axios' Andrew Freedman reports.

• The deadly tornado rampage that hit Tennessee and five other states over the weekend was powered by those trends.

Why it matters: Climate change is raising the odds of dangerous severe weather outbreaks across the South and Mid-South, particularly during the fall and winter when the jet stream dives toward the region.

• Our risk is gradually increasing compared to the Plains states, and tornado occurrence is becoming more variable from year to year. A new study shows that as temperatures increase, so do key ingredients for severe weather outbreaks.
• The weekend outbreak illustrates an extreme scenario of what can happen when all the ingredients that cause devastating tornadoes come together in spades. These include a record warmth combined with humid air mass and powerful winds that shift in speed/direction with height, known as wind shear.

The big picture: The latest outbreak stands apart from anything previously seen during the month of December. In some respects, what occurred was worse than anything that came before it, no matter what month you look at.

• The supercell thunderstorm that tracked for more than 250 miles from Arkansas into Kentucky spawned either a single tornado or a group of twisters that may have broken the record for the longest tornado path length in U.S. history.

• At least 88 people were killed, including 74 in Kentucky and four in Tennessee.

What's happening: It's not a coincidence that Friday night's outbreak came on a day of record warmth and high humidity throughout the Mid-South and South.

• In Memphis, the high on Friday was 80°F, a record high and 25°F above average for the date.
• The warm, humid air — more typical of April or May — created a powder keg that, when combined with a roaring jet stream and strong cold front, exploded.

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