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Credit & Copyright: Daniela Mirner Eberl   
   
Explanation:
What kind of cloud is this?     
   
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, a type of   
Arcus cloud,   
 is completely detached from their parent     
cumulonimbus cloud.     
   
Pictured   
above, a   
roll cloud extends far into the distance in 2009 January   
above Las Olas Beach in   
Maldonado,   
Uruguay.   
   
    
   
   
 Note:  An   
APOD editor will review astronomy images of 2009,   
   
hosted by the Amateur Astronomers Association of New York on Friday,   
January 8 at the American Museum of Natural History, NYC.   
   
   
   
   
   
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NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day
Publications with keywords: Roll cloud - weather
Publications with words: Roll cloud - weather
See also:

