What is a Shelf Cloud?

About Shelf Cloud:

• A “shelf cloud” or “Arcus cloud” generally forms along the leading edge of thunderstorms.
• It is a type of low-lying, horizontal cloud formation characterized by a clearly defined line of solid clouds.
• It is known for its distinctive wedge-shaped formation. They usually appear as a broad arc across the sky that can sometimes appear to be rotating horizontally.
• Formation: 
  • Shelf clouds form when cold and dense air is forced into a warmer air mass by wind.
  • This rush of cold air often occurs in a thunderstorm’s downdraught, where cold air rushes towards the ground before spreading out to create a gust front.
  • Shelf clouds produced by thunderstorms are always preceded by a rush of dry and cold air ahead of the cloud, with rain arriving after the shelf cloud has passed overhead.

What is a Thunderstorm?

• A thunderstorm is a rain shower during which you hear thunder. Since thunder comes from lightning, all thunderstorms have lightning.
• Formation:
  • Thunderstorms form when warm, moist air rises into cold air. 
  • The warm air becomes cooler, which causes moisture, called water vapor, to form small water droplets — a process called condensation.
  • The cooled air drops lower in the atmosphere, warms, and rises again.
  • This circuit of rising and falling air is called a convection cell. 
  • If this happens a small amount, a cloud will form. If this happens with large amounts of air and moisture, a thunderstorm can form.

Q1) What is an Air Mass?

Air mass, in meteorology, is a large body of air having nearly uniform conditions of temperature and humidity at any given level of altitude. Such a mass has distinct boundaries and may extend hundreds or thousands of kilometers horizontally and sometimes as high as the top of the troposphere (about 10–18 km [6–11 miles] above the Earth’s surface).

Source: Terrifying ‘Shelf Cloud’ Reportedly Forms Over The Skies In Haridwar; WATCH Viral Video

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