Derecho

In Context 

States of Nebraska, Minnesota and Illinois in the US were hit by a storm system called a derecho .

What is a Derecho?

•  According to the US’s National Weather Service,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. 
• These storms travel hundreds of miles and cover a vast area.
• Being a warm-weather phenomenon, a derecho generally – not always – occurs during summer time 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.
• Classification
  • For a storm to be classified as a derecho it must have wind gusts of at least 93 km per hour; wind damage swaths extending more than 400 km.
  • 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.
• Types 

• They fall into three categories –
  • A progressive derecho : It 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 : It has an extensive squall line – wide and long – sweeping across a large area. It usually occurs during spring or fall.
  • Hybrid : They have the features of both progressive and serial derechos.

• Occurrence 

• They mostly occur across central and eastern parts of the United States.
  • Derechos have also been documented elsewhere across the world.
  • They have also swept through Germany and Finland, and more recently in Bulgaria and Poland.

Source:IE