Predicting When Tornadoes Will Strike

By: Sciencedaily.com
By: Sciencedaily.com

This year has been one of the most active tornado seasons of the last 50 years. In the first half of the year alone, 118 people were killed by a tornado touchdown.

The unpredictability of tornadoes is worsening as they strike in places once considered unusual. In August, a tornado warning was even issued in New York City -- and touchdowns like these are keeping meteorologists busy.

Tragically, the aftermath of many tornadoes is devastating -- houses are destroyed, and buildings are flattened. Meteorologists at the NOAA Storm Prediction Center in Norman, Okla., study these destructive forces of nature and their weather patterns. They recently found some unique connections between sea surface temperature and where tornadoes form.

"During an El Niño event, the sea surface temperatures are warmer," says Ashton Robinson Cook, a meteorologist at the NOAA Storm Prediction Center. "During a La Niña event, the temperatures are cooler than normal." Scientists found that during El Niño events, tornado activity was in the Gulf Coast states and Central Florida, while tornado outbreaks were seen in southeastern Texas heading northeast into Illinois, Indiana and Michigan during La Niña events -- both events causing tornadoes in unlikely places. This new discovery addresses tornado patterns during El Niño or La Niña events -- although predicting when either will develop is tricky.

"We really don't know when El Niño or La Niña is going to occur -- until we see them actually developing," Cook says. This discovery will mean meteorologists can give the public more time to get ready.

"We'll be able to get the word out to the public with better time for them to react [and] better time to prepare -- and that ultimately would save lives," Cook says.

Reaction time makes all the difference when twisters are in the forecast.

ABOUT EL NINO: El Niño is a cyclical warming of the ocean waters in the central and eastern tropical Pacific that generally occurs every three to seven years, usually around the holidays. It is associated with changes in air pressure and the movement of high-level winds, and can affect weather worldwide. In the United States, En Niño normally results in warmer-than-normal temperatures across the northern and western states. Wetter conditions result in the south, with dry weather across the Ohio Valley and Pacific Northwest. El Niño typically peaks during the winter months. It alternates with La Niña, the cooling of ocean waters in the same region of the Pacific.

HOW TORNADOES FORM: Air is a gas and water is a liquid, but in the realm of science, both fall into the category of fluids. When a fluid's flow is disturbed, it causes turbulence. For instance, branches sticking into the water can disrupt the flow of a stream, forming tiny eddies or whirlpools. The same thing happens when you move your hand quickly through water. Technically, these are known as vortices. The water moves in a circular motion around a central point, and this causes a depression or cavity to form in the center, which draws flowing objects towards that center. Think of water spinning down the bathroom drain.

These sorts of swirling vortices can also form in air. As a thunderstorm develops, if the wind speeds up and changes direction, this can cause a horizontal spinning effect in the lower atmosphere. As air rises, pulled upwards by the developing thunderstorm, it tilts the horizontal rotation into a vertical rotation. A tornado is simply a violently rotating column of air that extends from a thunderstorm in the atmosphere to the ground. The pressure inside can be 10 percent lower than the surrounding air, and this causes that air to rush towards the low-pressure center from all directions. As it streams inward, the air spirals upward around the core until it merges with the airflow of the thunderstorm that gave rise to the tornado.


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