Monday, December 05, 2022

Explained: What is Derecho, a Hurricane That Turned the Skies Green in America?

In the US, the states of Nebraska, Minnesota and Illinois were hit by a storm system called Derecho on Tuesday. As the storm struck, winds gusting to about 140 kmph, power lines were snapped and trees were uprooted. As the storm approached, it turned the skies green, even as many experienced storm chasers claim to have never seen such atmospheric optics, according to the Washington Post. What is a derecho, how did it make America’s skies green?

What is Derecho?

According to the US National Weather Service a derecho is “a broad, long-lasting, straight-line thunderstorm” associated with a “band of rapid-moving rain or thunderstorms”. The name comes from the Spanish word ‘la derecha’ which means ‘upright’. Straight line storms are those in which there is no rotation, unlike thunderstorms. These storms travel hundreds of miles and cover a vast area.

Being a warm-weather phenomenon, derecho typically – not always – occurs during the summer starting in May, with most hitting in June and July. However, they are a rare occurrence compared to other storm systems such as tornadoes or hurricanes.

For a hurricane to be classified as a derecho it must have gusts of at least 93 kmph; The wind damage swath extends over 400 km. According to the University of Oklahoma’s School of Meteorology, the time interval between consecutive wind damage events should not exceed three hours.

Why did the sky turn green during the derecho that came to America recently?

Strong thunderstorms result in a ‘green sky’, which is caused by the interaction of massive amounts of light with water. A Washington Post report said that large raindrops and hail are believed to scatter all but the blue wavelengths, causing mainly blue light to penetrate beneath the storm cloud. The report said that this blue combined with the red-yellow color of the afternoon or evening sun gives the green color.

Are there different types of Derecho?

They fall into three categories – progressive, serial and hybrid. a progressive

The derecho is associated with a short line of thunderstorms that can travel hundreds of miles along a relatively narrow path. This is a hot summer event.

On the other hand, a serial derecho has a broad squall line – wide and long – spread over a large area. This usually happens during spring or fall.

Hybrid ones have characteristics of both progressive and serial derecho.

Where are derechos usually?

They occur mostly in the central and eastern parts of the United States.

May 8, 2009 The “Super Derecho” was one of the “most intense and unusual derechoes ever seen” in the US as it traveled from Kansas to Kentucky with wind speeds reaching 170 km/h.

Derechos have been documented elsewhere around the world. In 2010, Russia saw its first documented derecho. They have also flowed into Germany and Finland and more recently Bulgaria and Poland.

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