Published on : Thursday, March 18, 2021
A significant tornado outbreak is expected to hit much of the US Southeast in multiple waves Wednesday, according to the Storm Prediction Centre, which issued a rare “high risk” level warning.
Long-track, intense tornadoes are expected to begin in parts of Louisiana and Arkansas on Wednesday afternoon and then spread eastward and peak at night in Mississippi and Alabama, the centre said. Atmospheric conditions across the region make this threat for tornadoes as bad as it gets.
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Three million people are under this high level threat, and in all, about 45 million people are under a severe weather threat from the storms and could see tornadoes, large hail and damaging winds. Adding to the concern is that night-time tornadoes can be more given that people are sleeping and may be unprepared to take immediate shelter.
The risk level for tornadoes and severe storms was raised to the highest possible level — 5 out of 5 — a rare incident, the center says. The last such high risk was issued in May 2019 when the central Plains were hit with dozens of tornadoes and flash flooding.
As of midday Wednesday, a line of severe storms was moving into western Louisiana and Arkansas, prompting three separate tornado watches through the early afternoon.
Individual supercells will begin to develop ahead of that main line of storms from central Mississippi into central Alabama. This will be the most dangerous part of the outbreak, the center said, as these storms typically have the greatest potential to produce long-track, intense tornadoes.
A “particularly dangerous situation,” or PDS, tornado watch has been issued for parts of Alabama and Mississippi until Wednesday evening, according to the Storm Prediction Center. A PDS tornado watch is issued when the forecaster has high confidence that multiple strong or violent tornadoes (EF2 or higher) will occur in the watch area.
The main line of storms is then expected to continue eastward through Mississippi, Tennessee and Alabama through the evening. It will eventually reach Georgia in the overnight hours and then the Carolinas on Thursday.
A tornado watch means conditions are favorable for a tornado, while a tornado warning is more immediate and means one has been sighted or may be happening.