What's derecho – the storm that caused US skies to turn green

Earlier this week, skies over the states of Nebraska, Minnesota and Illinois turned green as if in a later Harry Potter film. It was no special effect or murderous dark wizards casting spells, but a storm system called a derecho.The storm, with winds gusting at around 140km per hour, snapped power lines and uprooted some trees as it rolled in. The skies turned green, a phenomenon many experienced storm chasers claimed to have never witnessed before, according to the Washington Post.What is a derecho?The US’s National Weather Service defines a derecho as “a widespread, long-lived, straight-line windstorm” that is associated with a “band of rapidly moving showers or thunderstorms”. The name that has Spanish origins from ‘la derecha’ means straight. Unlike a tornado in which winds rotate, a derecho is a straight-line storm without any rotation in its winds. These storms travel hundreds of miles and cover a vast area.A derecho generally occurs during summertime starting from May and increasing in frequency in June and May. There have been instances of derecho in colder weather too. However, a derecho is a rare occurrence as compared to other storm systems like tornadoes or hurricanes. A storm is classified as a derecho if it has wind gusts of at least 93 km per hour, wind damage swath extending more than 400 km. And, according to the University of Oklahama’s School of Meteorology, the time gap between successive wind damage events should not be more than three hours.There can be three different types of derechos – progressive, serial and hybrid. A 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.A 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 ones have the features of both progressive and serial derechos.The “Super Derecho” on 8 May, 2009 was one of the “most intense and unusual derechos ever observed” in the US as it swept from Kansas to Kentucky with wind speeds reaching up to 170 km/hr.Why did the sky turn green?According to The Indian Express, severe thunderstorms can turn the sky green due to light interacting with the huge amount of water they hold. As per a report in the Washington Post, it is believed that the big raindrops scatter 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, the report said.With inputs from agenciesRead all the Latest News, Trending News, Cricket News, Bollywood News,India News and Entertainment News here. Follow us on Facebook, Twitter and Instagram.