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ZimZam

Cloud Cover

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I saw a picture of Rainier with a mushroom cap cloud over just the peak. But only the peak no other clouds in the sky. What is this phenomena?

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It is called a lenticular (lens shaped) cloud, and it is caused by fairly dry fast-moving air, with laminar flow, interacting with the mountain so that it is forced upward in a smooth arc. The temperature drops just enough for the moisture to condense. As the air falls again on the lee side of the mountain, it warms back to its initial temperature and the cloud evaporates.

 

The reason that Rainier was the only peak with a lenticular cloud cap was because the air was too dry for any other peak but the highest to raise the air enough to cool it below its dew point.

Edited by catbirdseat

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i like the indian explanations better...

 

"big mountain make cloud angry! death to go up there, pale-face!"

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Nice Drew, Ya I geuss I posted a cap cloud and I bet the original poster saw a banner cloud.

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The pic I saw was a "cap cloud" similar to what you posted. Thanks for clarifing differences Dru. Now I know.

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i like the indian explanations better...

 

"big mountain make cloud angry! death to go up there, pale-face!"

 

"Skookum tillicum, skookum tumtum"

 

- Translation: Carry an MLU, WhiteBoy.

 

Conservation of energy: In a bounded packet of air, as the kinetic energy increases (with wind velocity) the pressure energy decreases accordingly. Conservation of Mass: Wind velocity increases when a packet of air has to take a longer route in the same time period to clear an aerodynamic obstruction, such as Rainier, relative to other packets of air in the same stream that can continue to travel in a straight line. Lower pressure air has less capacity to carry water vapor, so the rest precipitates out as water droplets (cloud) for those packets that much take the long way around. Once a given air packet has completed its trip over the obstruction and rejoined its straight line compatriots, wind velocity (and kinetic energy) drops back down, pressure energy increases, water vapor carrying capacity increases, and water droplets (cloud) evaporate back into water vapor.

 

Or sometimes it's just a UFO hovering over the Mountain.

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lenticular_small.JPG

 

Taken from inside a lenticular on Hood a few weeks ago. Time to run like hell. :noway: The wind was like nothing I've ever seen.

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