| What kind of cloud is this?
A type of
arcus cloud called a roll cloud.
These rare long clouds may form near advancing cold fronts.
In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form
a cloud.
When this happens uniformly along an extended front, a
roll cloud may form.
Roll clouds
may actually have air circulating along the
long horizontal axis of the cloud.
A roll cloud is not thought to be able to morph into a
tornado.
Unlike a similar
shelf cloud,
a roll cloud is completely detached from their parent
cumulonimbus cloud.
Pictured
above, a
roll cloud extends far into the distance as a storm approached in 2007 in
Racine,
Wisconsin, USA.
Credit:
Pierre cb,
Wikipedia
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