Very serious threat of strong, long-lasting tornadoes in southern U.S.

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The National Weather Service’s Storm Prediction Center has issued a moderate threat for severe weather Saturday. Moderate does not nearly convey the actual threat. On a scale of one to five, it’s a four. This is the kind of day we see in the U.S. only a handful of times each year.

The bullseye for the biggest threat is east Texas, Louisiana, southern Arkansas and central Mississippi. Within this area, and extending outward a couple hundred miles in every direction, there is a heightened threat for strong, long-track tornadoes.

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The parameters that meteorologists use to diagnose the severity of thunderstorms are calculated by how unstable the air is due to warmth and humidity, combined with the strength of winds. The numbers on Saturday, especially for something called the “significant tornado parameter,” are about as high as they get in areas near Louisiana.

An upper-level storm system, powered by strong jet stream winds aloft, is combining forces with warm and humid air surging north out of the Gulf of Mexico. The combination will be enhanced by any heating due to breaks of sun between thunderstorms. As mentioned, the biggest threat is tornadoes, but large hail, frequent lightning, flash flooding and damaging straight-line wind gusts are all likely.

The worst of the storms will be found Saturday afternoon over east Texas moving into Louisiana, Arkansas and Mississippi. On Saturday night that threat moves into Tennessee and Alabama where storms will still be able to produce strong tornadoes.

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Tornadoes are most dangerous at night because people often sleep through the threats. Also, you cannot see a tornado coming. Nighttime tornadoes are 2.5 times more likely to kill. Make sure your phone is on and ready to receive the latest warnings. Have a plan in place for the safety of your family.

On Sunday, the storm system will expand and move east. The thunderstorm threat area will be much broader from north Florida to Ohio and as far east as Pennsylvania, Virginia and North and South Carolina. Strong winds, large hail and a few tornadoes are possible. Overall the threat will be slightly less severe than Saturday’s but still should be considered significant.

Traditionally “Tornado Alley” has been centered on the lower Plain States. And although that area still has the highest concentration of tornadoes, the zone has been shifting east the past couple of decades. The greatest increase in tornadoes recently is being found in the Deep South in an area now called “Dixie Alley” up to the Tennessee Valley.

In 2018, research confirmed this shift is due partly to a warming Gulf of Mexico and shifting climate patterns related to climate change and potentially natural climate cycles as well. This is important because the Deep South is more vulnerable to severe weather with higher population density, structures that often aren’t sturdy and a greater likelihood that storms will hit during the night.