Shelf clouds are often associated with squall lines.
A stunning video of a huge mountain cloud covering the Brazilian city of Caxias do Sul has gone viral on social media. Shelf clouds, which have a round shape and appear to have layers, usually appear before storms. The clip was recorded by a local on Saturday morning and posted to Instagram and other social media platforms. The timelapse video shows how clouds pass over the buildings. They appeared due to the weather in the Brazilian city, which experienced thunderstorms, lightning and gusty winds, according to a report in G1.
Watch the video:
O dia virou noite,na Cidade de Caixas do Sul,Rio Grande do Sul. A nuvem gigantesca cobre a cidade. pic.twitter.com/Qz46ZYrE8L
— Sergio Batista (@sergiobp37) September 23, 2023
The outlet further said that winds from the ocean and instability associated with low pressure in Paraguay were responsible for the extreme weather in Rio Grande do Sul.
Temperatures also remained low in areas around the city, the outlet said.
The local weather office has forecast rain all day in the Brazilian state.
What are shelf clouds?
According to the National Oceanic and Atmospheric Administration (NOAA), shelf clouds are often associated with squall lines and are often reported as wall clouds, funnel clouds, or rotation.
Also called Arcs clouds, they are usually associated with a continuous line of storms: the wind comes first and then the rain follows. It may appear as if it rotates on a horizontal axis, NOAA said.
These clouds are sometimes seen beneath cumulonimbus clouds, the dense, towering vertical cloud that produces intense rain.
How are shelf clouds formed?
According to the UK Met Office, when a cold downward movement from a cumulonimbus cloud reaches the ground, cold air can spread quickly over the ground, pushing existing warm, moist air upwards. As this air rises, water vapor condenses in the patterns associated with shelf clouds.
The new cloud may roll if it experiences different wind directions above and below, the agency further said.
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