June 28, 2013
Typically, we think of severe storms as producing rain, lightning, and damaging winds with the occasional tornado. However, a severe thunderstorm is also capable of producing winds with speeds faster than 100 mph, even without a tornado. These powerful winds can be just as damaging and are known as straight-line winds.
A storm that is capable of producing consistent straight-line winds of 58 mph or more and covers an area of more than 240 miles is known as a derecho. Powerful gusts can cause heavy damage to cars and buildings. The storm’s dynamic straight-line winds can also knock down trees and power lines, possibly injuring people nearby, similar to the damage caused by tornadoes.
On May 31, 1998, an extremely powerful derecho hit Wisconsin and Michigan with wind gusts of up to 130 mph, equal to the speeds of an EF-2 tornado, causing millions of dollars in damage.
Severe thunderstorms can produce short, but extremely damaging, straight-line wind events known as microbursts. A microburst is a very small area (less than 2.5 miles in diameter—think a couple of neighborhood blocks) of very strong winds that last for anywhere from a few seconds to several minutes. These intense wind pockets can produce gusts of up to 150 mph. During a microburst’s relatively brief lifespan, wind speeds can be comparable to an EF-3 tornado or Category 4 hurricane.
While straight-line winds are different than tornadoes, they can cause just as much damage. It’s important to pay attention to warnings from your weather alert radio in the case of high winds. Derechoes can form quickly and move at speeds of up to 70 mph, leaving you little time to prepare or take shelter.
Like a tornado, straight-line winds and derechos are particularly dangerous if you’re caught outdoors during the storm. Immediately seek shelter, and stay away from trees or large objects that could topple over on you. Mobile homes and vehicles are also susceptible to high winds, which may blow them across or even off the roads. In an urban area, these high winds can knock down power lines, creating a serious danger for those nearby. Never, ever attempt to approach or drive over a downed power line.
Severe thunderstorms producing lightning and high winds can easily cause power failures. Utility poles are blown over or trees topple on the lines. The best, most reliable way to ensure you’re alerted to severe weather threats in the middle of the night or when the electricity is out is a weather alert radio with either an emergency crank or battery back up power.