Weather – April 2017

Derecho

Do you know what a derecho is? Derechos are widespread, long-lived windstorms with
a band of rapidly moving showers or thunderstorms. The phenomenon was discovered and named by Dr. Gustavus Hinrichs, a German immigrant living in Iowa. Derecho (pronounced like “deh- REY-cho” in English) is a Spanish word which means “direct,” or “straight ahead.” This relates to the type of destruction that derechos can cause, as their damage patterns occur along generally straight lines. This is known as “straight-line wind damage.”

Derechos often occur within storms that have a curved shape when viewed on radar. These are called “bow echoes” because their curved shape resembles an archer’s bow. Derechos come from either one strong bow echo or a series of bow echoes. If the bow echo (or a series of bow echoes) travels more than 250 miles or produces wind gusts of 58 mph or more, it is classi ed as a derecho.

Several well-known derechos have occurred over the past few decades. On March 12, 1993, a strong low-pressure system dubbed the “Storm of the Century” formed in the Gulf of Mexico and produced a serial derecho that swept across Florida and Cuba. The “Right Turn” derecho a ected North Dakota July 12, 1995, with winds of 91 miles per hour that knocked down over 5 million trees and damaged many buildings.

On May 8, 2009, the “Super Derecho” storm caused damage from Kansas to Kentucky, with winds measuring 90 miles per hour and widespread ooding. On June 29, 2012, there was a major derecho event which a ected Ohio, Virginia, Pennsylvania, West Virginia, D.C., Maryland and New Jersey, causing widespread damage and millions of power outages. This storm helped popularize the term “derecho” with the public.

So, what can you do to keep yourself safe? If a derecho is headed your way, the National
Weather Service will issue a Severe Thunderstorm Warning. You are most vulnerable to a derecho outdoors or in a vehicle.

If a Severe Thunderstorm Warning is issued, take shelter inside and stay away from windows. It’s a good idea to have a disaster supply kit ready as power outages are very
likely with derechos. Your kit should include food and water, flashlights and batteries, a spare battery for your cellphone, a rst-aid kit, a list of emergency contacts and a battery-powered weather radio.

If you’re planning to spend time outside, check the forecast before heading out to see if there are any storms on the way. In fact, it’s a good idea to check the forecast each day after waking up in the morning, so that you’ll always be prepared. Your forecast is always available on www.weather.gov, or you can check with your local NWS forecast o ce.

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