This unique meteorological phenomenon is called a roll swarm , and it ’s assure here make its forth over the city of Calgary , Alberta . Though it appear like a tornado that has fallen down , it ’s really a type of arcus senilis swarm — a slow and horizontal cylindrical structure that often appear ragged and turbulent .
The National Weather Servicedescribes the roll cloud like this :
A low , horizontal electron tube - shaped arcus cloud associated with a thunderstorm gust front ( or sometimes with a stale front ) . Roll clouds are relatively rare ; they are completely come away from the thunderstorm base or other swarm features , thus differentiate them from the more familiar shelf clouds . axial rotation clouds ordinarily come out to be “ rolling ” about a horizontal axis , but should not be befuddle with funnel clouds .
[ ViaEPOD ]
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