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Tornadoes and how they're formed

Tornadoes are as hard to predict as they are to forget after experiencing one. These mysterious whirlwinds can look like ordinary clouds, hide behind heavy rain, and even touch ground in a snowstorm. Keep reading to learn how tornadoes are formed and what myths get stuck in their vortex. Remember: you can always check Weather for current weather forecasts.

What are tornadoes?

Tornadoes are rotating columns of air that form in a thundercloud cloud and spiral downwards. The diameter of the lower funnel reaches an average of 400 meters and depends on where the tornado travels: about 5–30 meters over water, or 1.5–4 km on land. When a tornado is formed over water, meteorologists refer to it as a waterspout.

How tornadoes are formed?

Even today, scientists are still uncertain exactly how and why tornadoes form. The general belief is that most tornadoes come from mesocyclones when warm and cold air collide. It looks like if another cloud appears under the base of the thundercloud behind the section where precipitation is visible.

Due to the powerful updraught and downdraught in this cloud, particles start moving rapidly enough to form a column of violently rotating air. A stream of warm air descends inside the funnel, and cold air envelops it around the outside edges.

An area of low pressure forms in the center of the vortex, causing the descending whirlwinds to start acting like a vacuum cleaner, sucking in everything in their way. For example, the large amount of moisture that rises along with updraughts of cold air form a condensation funnel, helping make the tornado visible.

However, sometimes tornadoes can be formed even without any temperature differences.

It's impossible to measure the speed of air in the funnel, but studies show that it's usually under 50 m/s with the potential to reach up to 100 m/s. Tornadoes move along with the thundercloud they're formed from. The longest tornado in history was the Tri-State Tornado, a vortex lasting 3.5 hours that covered 350 km from start to finish. Where the lower funnel meets the surface of land or water, there can be a small cloud of dust, debris, or condensation rising upward. After reaching a certain height, everything picked up by the wind falls back down. Tornadoes look a lot like a rope, whip, or long cloud. Tornadoes hidden by heavy rain or forming at night are especially dangerous and can only be detected by sound or weather radar. The color of the funnel depends on the surface: over land tornadoes get gray or white, while waterspouts are white or dark blue. Tornadoes can form on every continent and in many countries. They're most often seen in the U.S., Argentina, and Bangladesh. In Russia, they mostly touch down in the western part of the country in the summer.

Types of tornadoes

Here are some types of whirlwinds that can occur:

• Rope tornado: Long, thin, and often winding in appearance.
• Wedge tornado: Look like ragged clouds and are wider than they're long.
• Multi-vortex tornado: Form from two or more columns around the central vortex.

Based on how they're formed, tornadoes can be:

• Waterspouts: Formed over the surface of seas, oceans, and occasionally lakes.
• Fire whirls: Formed from clouds during volcanic eruptions or strong fires.
• Snow devils: Formed during strong blizzards.
• Landspouts: Formed in cumulonimbus clouds when the water temperature is much warmer than the air above the clouds.
• Funnel clouds: Made of condensed droplets of water.
• Gustnado: Not connected with clouds. Formed when cold, dry air under a cloud collides with warm, moisture-rich air near the land's surface.
• Steam devils: Formed over warm bodies of water when the air above them gets very cool.
  There are several different types of scales to measure tornadoes. The most common is the Fujita Scale, with F0 and EF0 tornadoes categorized as the weakest. Category F5 and EF5 tornadoes are the most violent and can tear houses off their foundation and even damage skyscrapers. In Europe, tornado intensity is measured on the TORRO scale from T0 to T11.

Tornado myths and misconceptions

These destructive forces of nature have a lot of legends surrounding them: — Many people think that green skies mean a tornado is coming. While this phenomenon may be related to severe weather, scientists have found no evidence linking the unusual color to tornadoes. — It's a common misconception that opening a window will reduce the damage from a tornado. While atmospheric pressure does drop significantly inside a tornado, the pressure difference is unlikely to cause much harm by itself. In fact, opening windows can increase the severity of damage, as a strong tornado can destroy a home whether the windows are open or not. — Contrary to common belief, tornadoes can occur not only in open areas, but also in cities. In 1999, this was confirmed when a strong tornado hit Salt Lake City. There's also no point in hiding under freeways, as that same year a powerful tornado in Oklahoma claimed several lives. — In fact, even large natural objects are unable to protect people against a tornado. There are cases when tornadoes crossed large rivers and even climbed mountains.