Subj : Daily APOD Report
To   : All
From : Alan Ianson
Date : Sun Aug 20 2023 01:05:50

                        Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2023 August 20
     Building in a city are pictured. Above the buildings appears a long
       dark cylindrical cloud that goes to the horizon. Please see the
                 explanation for more detailed information.

                         A Roll Cloud Over Wisconsin
                Credit: Megan Hanrahan (Pierre cb), Wikipedia

   Explanation: 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
   here, a roll cloud extends far into the distance as a storm approaches
   in 2007 in Racine, Wisconsin, USA.

                      Tomorrow's picture: comet unknown
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

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