Note4Students

From UPSC perspective, the following things are important :

Prelims level: Derecho

Mains level: Not Much

States of Nebraska, Minnesota and Illinois in the US were hit by a storm system called a Derecho which turned the skies green.

A derecho is a widespread, long-lived, straight-line windstorm that is associated with a band of rapidly moving showers or thunderstorms.
The name comes from the Spanish word ‘la derecha’ which means ‘straight’.
Straight-line storms are those in which thunderstorm winds have no rotation unlike a tornado.
Being a warm-weather phenomenon, a derecho generally – not always – occurs during summertime beginning May, with most hitting in June and July.
However, they are a rare occurrence as compared to other storm systems like tornadoes or hurricanes.

Severe thunderstorms result in a ‘green sky’ due to light interacting with the huge amount of water they hold.
The big raindrops and hail scatter away all but the blue wavelengths due to which primarily blue light penetrates below the storm cloud.
This blue then combines with the red-yellow of the afternoon or the evening sun to produce green.

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

Progressive derecho is associated with a short line of thunderstorms that may travel for hundreds of miles along a relatively narrow path. It is a summer phenomenon.
Serial derecho, on the other hand, has an extensive squall line – wide and long – sweeping across a large area. It usually occurs during spring or fall.
Hybrid derecho are that ones have the features of both progressive and serial derechos.

They mostly occur across central and eastern parts of the United States.
Derechos have also been documented elsewhere across the world.
In 2010, Russia witnessed its first documented derecho.
They have also swept through Germany and Finland, and more recently in Bulgaria and Poland.

Derecho: A storm that turned the sky green in the US

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