March is known for its extremely volatile weather, as the warm spring conditions struggle to replace the cold of winter. When and where the collision between the two meet, there will likely be weather and tornadoes.
This general collision in March is scheduled to occur from Tuesday to Thursday in the southern United States, with a particularly dangerous outbreak of severe weather Wednesday and Wednesday night from Arkansas east to Alabama. There is a threat of numerous tornadoes, with some large and powerful tornadoes possible.
On Wednesday morning, NOAA’s Storm Prediction Center issued a ‘high risk’ warning – 5 out of 5 on the warning scale – saying: ‘Long, intense tornadoes are expected, along with damaging winds and heavy hail’. parts of Louisiana and Arkansas, and moving eastward to Mississippi and Alabama at night.
There has been no ‘high risk’ warning since 2012. It is just as dangerous as it gets, with widespread, devastating and potentially deadly tornadoes.
For forecasters, it is no surprise that the spring season is starting with a bang. This is because there is another formidable La Niña event present in the tropical Pacific, which is usually accompanied by a more extreme undulating jet stream and thus an increased tornado threat.
Tornadoes are also more common in March. This past weekend, as historic snowfall Denver and Cheyenne plastered, the same storm built 19 tornadoes in the Panhandle of Texas. In a 2015 paper, researchers found that the onset of the tornado season had increased by 13 days since the late 1970s.
And the threat of the tornado shifts not only in time but also location. A 2018 study found that there is a declining trend of tornadoes in what is traditionally known as Tornado Alley in the Plains states, but a increasing trend of tornadoes occurring in the Middle South – the same general area that is expected to face the serious outbreak of this week.
The danger may already be increasing in this region. Two of the deadliest tornado outbreaks in the past two years occurred in early March in the Southeast. In 2019, 41 tornadoes concentrated in Alabama and Georgia 23 people killed. In 2020 there was 25 deaths while 15 tornadoes tore across Tennessee.
This week’s threat
The main features of this storm are both the pool of cold air rising and the fact that it turns like a peak. The cold air upwards allows the hot air on the surface to rise faster, creating larger thunderstorms. The rotational motion of the storm helps to transmit rotational motions to the individual thunderstorms and any tornadoes that may cause them.
Usually these rotating storms lift northeast into the Mississippi Valley, but this storm cannot due to an atmospheric block in the north. Instead, it will move further east on Wednesday and Thursday, bringing with it strong dynamics across the Southeast, posing the threat of a widespread outbreak and particularly dangerous situation.
The main event will occur as the cold-spinning storm shifts eastward and collides with hot humid air pouring out of the Gulf of Mexico.
In addition to the “high-risk” bullseye, the Storm Prediction Center highlighted a wide area for an “increased risk” of severe weather – a 3 out of 5 – from southern Missouri southeast to the Florida Panhandle.
CBS News
Buried in the larger extended area is a greater risk, seen in red on the map. It’s technically called a ‘moderate risk’ and it’s an abnormally large risk area – but the name is misleading. A moderate risk is a 4 out of 5 on the weather scale and indicates the possibility of very dangerous severe storms. These include cities such as Little Rock, Memphis, Tupelo and Birmingham.
If you live in one of these risk areas, pay attention to local warnings and remember that storms will become even more dangerous as the night falls and the tornadoes become more difficult to spot. Computer models do indicate that the threat to major tornadoes will be maximal on Wednesday evening and night.
CBS News
Night tornadoes are more common in the Mid-South. This is because, unlike the drier plains that rely on the heat of daylight to provide energy for thunderstorms, the area adjacent to the Gulf of Mexico due to extra humidity can have a more energetic and unstable atmosphere much later in the night. maintain.
The threat of severe weather will continue until Thursday as the system shifts to Georgia and the Carolinas, where again tornadoes, damaging winds, hail and lightning are likely.
CBS News
Southeast more vulnerable to tornado damage
There are a variety of reasons why tornadoes are more dangerous and destructive in the southeast, besides the greater tendency for them to happen at night. This greater vulnerability is the reason why trends in more and more severe storms in this region is important.
Because these storms form in a wetter environment, they tend to wrap up in rain and are harder to see. In addition, unlike the plains, where the terrain is often wide open and allows people to see tornadoes from miles away, the southeast is covered with more hills and trees.
The region also has a higher population density and much weaker homes, which increases the risk of damage and death. Research finds that this danger will continue to grow as the building continues to expand and the distribution of tornadoes changes, with a threefold increase in disaster potential by the end of the century.
While scientists are still trying to figure out why tornado patterns change, there is ample research showing that dangerous storms, and the environments in which they form, are increasing, at least in part due to human climate change.
A 2016 study showed that the frequency of tornado outbreaks has been increasing since the 1960s and that the most extreme outbreaks are increasing at the fastest rate. And it is outbreaks, as opposed to individual tornadoes, that are most devastating, with 79% of the fatal tornadoes from 1972 to 2010 in outbreaks.
Probably the most revealing article on tornado trends was published in 2018 by dr. Victor Gensini and dr. Harold Brooks published. Their research shows a clear increasing trend in tornadoes in the Mid-South and Lower Mississippi Valley – an area that, as mentioned above, is particularly vulnerable. The biggest increase is close to cities like Little Rock, Arkansas; Memphis, Tennessee; Tupelo, Mississippi and Tuscaloosa, Alabama. This corresponds to the biggest threat area on Wednesday.
CBS News spoke to Gensini, an extreme weather researcher at the University of Northern Illinois (NIU). He says his research shows that a local area as large as a city in the Mid-South can experience an average of 4 extra tornadoes per decade than it did just 40 years ago.
In the image below, taken from Gensini’s paper and adapted by NIU, the red shadow indicates where tornadoes are increasing – almost exactly zero for Wednesday’s expected outbreak.
Gensini, Brooks 2018
In the blue shadow area, the numbers of tornadoes are declining in Texas and in the lower plains. While that area – commonly referred to as Tornado Alley – still has the highest density of tornadoes, the increasing trend in the east is being weighed.
Although Gensini can not say with certainty why the eastern trend is taking place, he does say so. in line with what we would expect from climate change. This is because the arid desert areas in the southwest extend eastward toward the warm climate. This limits the instability over the plain conditions, and therefore also the formation of tornadoes, and it pushes the convergence zone between dry and moist air to the east.
In addition, the waters of the Gulf of Mexico and adjacent land areas are warming due to man-made climate change. This influx of more heat and moisture provides increased energy to provoke more extreme tornado outbreaks in the southeast.
And while humans continue to warm the climate, most of science agrees that the environment created by these dangerous tornadoes will become increasingly unstable and dangerous.