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The Fierce Winds of Bow Echos

In May of 1996, a storm raced across South Dakota toppling nearly 600 power poles with wind speeds of more than 115 mph (185 km/hr). Just a year earlier, a storm with wind speeds up to 104 mph (167 km/hr) developed over Ontario, Canada and rolled across upstate New York and New England, killing 8 people and flattening Adirondack forests.

The term derecho was coined in the late nineteenth century to describe severe windstorms like these that travel hundreds to thousands of kilometers, producing wide swaths of damage along their path. Today, most of these convective windstorms are called bow echoes, named for their distinctively bow-shaped appearance on radar displays. They may occur on their own or with other bow echoes in an MCS squall line.

Traveling from west to east, these exceptionally ferocious storms torment the Midwest typically during the warm spring and summer months from May to August. Between January 1995 and July 2000 they were responsible for 72 deaths, 1008 injuries, and 1.4 billion dollars in property damage in the United States.

Read on to find out how bow echoes are able to produce such monstrous winds as well as spawning mesoscale convective vortices and tornadoes.