States of Nebraska, Minnesota and Illinois in the US were hit by a storm system called a Derecho which turned the skies green.
What is a Derecho?
- 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.
Why does the sky turn green during the derecho?
- 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.
Are there different types of derechos?
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.
Where do derechos usually occur?
- 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.
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