You never know when the sky will fall

Is Tornado Alley shifting east? Experts seem to think so. Climate change is deemed responsible.

An incredible funnel cloud storm system swept up Friday evening from East Arkansas north through the Missouri Ozarks and northeast to Kentucky, with a small spur shooting northeast to an Amazon warehouse near St. Louis. The twisters that touched down -- including a mammoth one that devastated towns along a 200-mile path into west Kentucky -- left a big toll of death and misery in their wake. Curiously, the killer tornados did not achieve the highest wind velocity rating of F5. They were EF3 or lower. But what the killer twisters lacked in vortex speed, they generally made up for in the power stemming from their gigantic sizes.

A CNN weather map shows the formative stages of the ferocious twister system that was about to ensue.

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Even today, a number of fading survivors and bodies may still lie under rubble in a string of pulverized towns.

The storm system flew rapidly above much of the Ozarks, but became much more dangerous as it encountered flatter countryside well east of Springfield and into Kentucky. The bulk of the system seems to have followed a northeasterly line from the lower Ozarks to Kentucky, while another branch shot north toward St. Louis.

But Friday's twister mayhem cannot definitively be ascribed to climate change, though those of us who live in Missouri, west Kentucky, west Tennessee and south Illinois may well be in for more twister touchdowns in future years. Still, the December storm system was certainly far from a routine affair, as explained by WDRB's meteorologist, Hannah Strong:

WHAT HAPPENED

In the upper levels of the atmosphere, the jet stream was moving at roughly 140 mph above our heads as a jet streak was developing. A jet streak is an area of stronger wind embedded within the overall flow pattern. That jet streak created significant movement in the atmosphere. 

The low level jet was CRANKING up to 95 mph less than a mile above our heads. With such strong upward motion in the atmosphere, all you need to do is get a small horizontal roll to develop closer to the surface and you will have a tornado. With both speed and directional shear, those horizontal rolls materialized and were picked up by the updrafts of these supercell storms. 

A weather map from WDRB shows the dynamics of the storm system's formation.

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The wind at the surface was moving in from the south bringing temperatures and dewpoints into the lower 60s as we moved toward midnight. That's true in central Kentucky, but in western Kentucky the wind direction curved slightly. Observations last night suggest the wind might have been coming more out of the south/southwest and curved back to the south. Those small disturbances in wind direction and speed are all that's needed to create rotation for a tornado. After the supercell formed in Arkansas, it moved through untouched air until it got to us. That's warm, moist air that was still getting warmer and more saturated even into the evening. That is gasoline to a supercell, so it continued to feed until it got to central Kentucky. That was a region that had already seen rain and storms within the last several hours, so it cut off some of that fuel supply and the storm changed a bit.

HOW UNUSUAL

We have actually seen tornadoes in Kentucky in December before. This link lists all December tornadoes for our area. The strongest was an F3 in Perry county (Indiana) but it crossed through Daviess county (Kentucky). That happened on Dec. 9, 1952. Ohio County, Ky, saw an F2 on Dec. 4, 1916. In 2018 we had an EF1 tornado in Harrison County, Ind., but the most recent December tornado in Kentucky was an EF1 in 2013. There were actually three EF1 tornadoes in Kentucky on Dec. 8, 2013. If any of the tornadoes in our area on Friday night are stronger than an EF3, that will be the strongest December storm for us. [The two tornado wind scale abbreviations stand for Fujita scale and Enhanced Fujita scale, which replaced the Fujita scale in 2007.]