Guess the Arcus…
By Joe Filakovsky on May 16, 2012, 1:42pm
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Imagine looking out your office window several stories up and see a darkening sky and appearance of a long cloud structure, rolling, actually almost boiling in appearance toward you. You can’t see a cloud structure behind it but visibility is poor and one might be there. The cloud reaches your building and there is a quick drop in air temperature accompanied with vigorous thunder and lightning. It blows by and then it becomes calm
I am fairly certain that the turbulence accompanying this cloud was a gust front or outflow boundary but shelf clouds indicate warm air which rises in front of the outflow boundary, defining the leading edge of the approaching storm; roll clouds, which may also form from shelf clouds appear detached from the storm, indicate a sinking of cold air which forces warm moist air to higher levels of the atmosphere forming clouds. In many cases, the relatively rare roll cloud accompany calm weather, frequently associated with a sea breeze….but they can be associated with the outflow boundary preceding a squall line (line of thunderstorms)
Except for the rolling, my inclination would be to call this a shelf cloud but please feel free to leave your thoughts!
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