Tornadoes in the USA: beginning of the high season
The beginning of the most active season on the Tornado Alley :
A major episode of severe thunderstorms and tornadoes affected the central United States this Friday, April 29, 2022 with many cases causing very significant damage.
The second half of April, the month of May and part of June are the most dangerous period for tornadoes on the Tornado Alley plains.
During this period, the atmospheric conditions are indeed recurrent with low-pressure zones descending from the Rocky Mountains and bringing cold air aloft to meet the increasingly warm and humid air coming up from the Gulf of Mexico. When these two air masses meet, violent thunderstorms form and can, when conditions are right, generate numerous tornadoes over the central United States.
Tornadoes are possible throughout the year over the United States, but conditions are much more favorable between April and June over the Great Plains, with increasingly important air mass conflicts and very dynamic and recurrent thunderstorm situations. Thus, it is during the month of May that the average number of tornadoes is the most important over the country.
Episode of severe thunderstorms and major tornadoes this April 29, 2022 :
This April 29, a very favorable situation presented itself over the central United States with a fairly hollow low pressure system overhanging the Rocky Mountains and accompanied by very cool air aloft. Ahead, the establishment of a south/southwest flow also caused the upwelling of warm and humid air from the Gulf of Mexico, resulting in a very strong air mass instability.
All the ingredients were thus gathered to generate a very strong instability of the air mass and thus a powerful thunderstorm degradation, in particular between Oklahoma, Kansas and Nebraska. The American weather forecasting services had therefore issued a Moderate Risk between Kansas and Nebraska with a significant risk (15%) of strong tornadoes, giant hail storms, heavy rain and powerful wind gusts.
Unfortunately, the forecasts were confirmed over these areas with the formation of numerous supercell thunderstorms in the afternoon of April 29 over the above mentioned areas. These severe thunderstorms quickly produced the first destructive hail, especially in Kansas:
In addition to the giant hailstones, several tornadoes were also recorded at the end of the day on April 29. According to a first report, at least ten tornadoes occurred between the East and the North of Kansas and 3 over the South of Nebraska.
The most impressive and destructive one, however, occurred in the late afternoon near Wichita, Kansas, forming under a powerful supercell thunderstorm moving over the region.
The community of Andover in the suburbs of Wichita was the most affected by this tornado, as it passed directly over a very populated area.
In this area, the damage was sometimes very significant with more than a hundred homes affected, sometimes destroyed, dozens of trees uprooted and vehicles sometimes lifted and thrown over several meters.
In addition to the numerous damages to the infrastructure, the report states that several people were injured in the township, including at least one person who was seriously affected. For the moment, no casualties have been reported.
According to the photographs of the damage in the area, this tornado is of high intensity, reaching at least the EF-3 or EF-4 stage, inducing winds of over 250km/h.
It is also important to remember that this same area was hit by an extremely powerful tornado 31 years ago almost to the day. On April 26, 1991, an F5 tornado (winds of more than 420km/h) moved between Wichita and Andover, causing particularly severe damage and 17 victims.
New risk of tornadoes and severe thunderstorms in the next few days :
The arrival of the month of May rhymes with the high season for tornadoes and severe thunderstorms in Tornado Alley. In the next few days, new severe thunderstorms are expected over the Great Plains. This Saturday, new severe thunderstorms, following the deterioration of this Friday, April 29 are expected from Arkansas to Illinois with a new risk of tornadoes, heavy hail, strong wind gusts and flooding.
However, it is from Sunday onwards that the situation will become very stormy again in the Tornado Alley plains with the arrival of a new low-pressure area through the Rocky Mountains towards the central United States. This situation will once again prove to be conducive to tornadoes at least until the middle of next week.