What if an F4 tornado hits Pakistan

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A super cell over Oklahoma developed into a devastating tornado that then passed south of Oklahoma City. The picture was taken on May 20, 2013 at 2:40 a.m. local time (9:40 p.m. CEST) when the tornado struck its deadly path of leaves. Image: NASA

On Monday, a particularly strong tornado caused many deaths and enormous devastation. The center of the action was Oklahoma City. The suburb Moore, which was almost completely razed to the ground, was particularly hard hit.

The first ground contact of the tornado was recorded at 2:56 p.m. local time in Newcastle, south of Oklahoma City. The tornado then moved on to Moore, a suburb of Oklahoma City, about 10 miles away. The tornado was on the ground for about 40 minutes. The warning time for the population was around 15 to 16 minutes. This corresponds to the requirements of the national weather service of the USA (NOAA), which stipulates that the population is specifically warned at least 15 minutes before a tornado. This then activates a sophisticated alarm system. A siren alarm is triggered, police and fire brigades drive through the streets to ask people to go to shelters. The national weather service operates its own radio station, NOAA Radio, where the tornado warnings are broadcast.

Tornadoes are not uncommon in this region; experts even refer to it as the tornado avenue. The reason for this is that very warm and humid air masses from the south meet significantly colder air masses from the north. This results in strong thunderstorms. The angular momentum that gives rise to tornadoes in the first place comes when the wind speeds increase considerably with height and, at the same time, the wind direction changes with height.

In the current case, the air in Oklahoma had heated up to almost 30 degrees during the day - and that with a humidity of 75%. When air masses 10 degrees colder entered this region from the north, the prerequisites were created. The tornado quickly developed into a vortex of strength F4 to F5 and thus belongs to the category of devastating tornadoes.

By the way, Moore was devastated in 1999 by an F5 tornado. The tornado at the time killed 39 people and caused billions of dollars in damage.

Why did the weather conditions yesterday cause tornadoes?

Well - in general, these structures are not unusual in connection with thunderstorm fronts. The most important ingredient is already there in strong thunderstorms: deep convection of moisture!

So that the moist air can also be transported to great heights, there must be a sufficiently strong decrease in temperature with height. The latent heat present in the water vapor, which is released during condensation, provides the necessary energy.

Rotating storm clouds can create tornadoes:
Although meteorologists around the world have been researching tornadoes for decades, it is still not clear how they arise. A well-known prerequisite for the development of strong tornadoes are particularly rare thunderclouds rotating around a vertical axis. These so-called super cells have a diameter of 20 to 30 kilometers. In addition, the supercell must have a cloud base close to the ground, as well as an increase in wind speed and a change in wind direction from the ground up to a height of around five to six kilometers. Only then are there suitable conditions for tornadoes to develop. However, no more than ten percent of all supercells produce tornadoes.

If you click on [more] in the "Topic of the day" section on the right, you will find a graphic showing the development of a tornado.

Dipl.-Meteorologist Andreas Friedrich DWD Tornado Officer

Press office
German Weather Service
Prediction and advice center
Offenbach, May 21, 2013

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