﻿ Astronomy Picture of the Day [1]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 [2]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 ([3]Pierre cb), [4]Wikipedia Explanation: What kind of cloud is this? A type of [5]arcus cloud called a [6]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 [7]rise, cool below its [8]dew point, and so form [9]a cloud. When this happens uniformly along an extended front, a [10]roll cloud may form. [11]Roll clouds may actually have air circulating along the [12]long horizontal axis of the cloud. A [13]roll cloud is not thought to be able to morph into a [14]tornado. Unlike a similar [15]shelf cloud, a roll cloud is completely detached from their parent [16]cumulonimbus cloud. [17]Pictured here, a [18]roll cloud extends far into the distance as a storm approaches in 2007 in [19]Racine, [20]Wisconsin, USA. Tomorrow's picture: comet unknown __________________________________________________________________ [21]< | [22]Archive | [23]Submissions | [24]Index | [25]Search | [26]Calendar | [27]RSS | [28]Education | [29]About APOD | [30]Discuss | [31]> __________________________________________________________________ Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell ([35]UMCP) NASA Official: Phillip Newman [36]Specific rights apply. [37]NASA Web Privacy Policy and Important Notices A service of: [38]ASD at [39]NASA / [40]GSFC, [41]NASA Science Activation & [42]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2308/rollcloud_hanrahan_3072.jpg 3. https://commons.wikimedia.org/wiki/User:Pierre_cb 4. https://en.wikipedia.org/wiki/File:Roll-Cloud-Racine.jpg 5. https://en.wikipedia.org/wiki/Arcus_cloud 6. https://epod.usra.edu/blog/2011/11/roll-cloud-shelf-cloud.html 7. http://neveryetmelted.com/wp-content/uploads/2013/09/LaundryCat.gif 8. https://en.wikipedia.org/wiki/Dew_point 9. https://www.youtube.com/watch?v=hKI2Atj08Xk 10. http://en.wikipedia.org/wiki/Roll_cloud 11. https://apod.nasa.gov/apod/ap090824.html 12. https://apod.nasa.gov/apod/ap060117.html 13. http://www.weatherscapes.com/album.php?cat=clouds&subcat=roll_cloud 14. https://apod.nasa.gov/apod/ap050613.html 15. https://apod.nasa.gov/apod/ap080122.html 16. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/vrt/cb.rxml 17. http://commons.wikimedia.org/wiki/File:Roll-Cloud-Racine.jpg 18. https://epod.usra.edu/blog/2006/04/lovelock-roll-cloud.html 19. https://youtu.be/b2ezPLnsRxk 20. https://en.wikipedia.org/wiki/Wisconsin 21. https://apod.nasa.gov/apod/ap230819.html 22. https://apod.nasa.gov/apod/archivepix.html 23. https://apod.nasa.gov/apod/lib/apsubmit2015.html 24. https://apod.nasa.gov/apod/lib/aptree.html 25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 26. https://apod.nasa.gov/apod/calendar/allyears.html 27. https://apod.nasa.gov/apod.rss 28. https://apod.nasa.gov/apod/lib/edlinks.html 29. https://apod.nasa.gov/apod/lib/about_apod.html 30. https://asterisk.apod.com/discuss_apod.php?date=230820 31. https://apod.nasa.gov/apod/ap230821.html 32. http://www.phy.mtu.edu/faculty/Nemiroff.html 33. http://www.phy.mtu.edu/ 34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 35. http://www.astro.umd.edu/ 36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 37. https://www.nasa.gov/about/highlights/HP_Privacy.html 38. https://astrophysics.gsfc.nasa.gov/ 39. https://www.nasa.gov/ 40. https://www.nasa.gov/centers/goddard/ 41. https://science.nasa.gov/learners 42. http://www.mtu.edu/