WW2010
University of Illinois

WW2010
 
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> online guides
 
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  current weather
 
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  index

Online Guides
 
  introduction
 
> meteorology
 
  remote sensing
 
  reading maps
 
  projects, activities

Meteorology
 
  introduction
 
  air masses, fronts
 
> clouds, precipitation
 
  el nino
 
  forces, winds
 
  hurricanes
 
  hydrologic cycle
 
  light, optics
 
  midlatitude cyclones
 
  severe storms
 
  weather forecasting

Clouds, Precipitation
 
  introduction
 
  development
 
> cloud types
 
  precipitation

Cloud Types
 
  introduction
 
  high-level clouds
 
  mid-level clouds
 
  low-level clouds
 
> vertically developed
 
  other cloud types

Vertically Developed
 
> fair wx cumulus
 
  cumulonimbus

User Interface
 
  graphics
> text

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Fair Weather Cumulus Clouds
puffy cotton balls floating in the sky

Fair weather cumulus have the appearance of floating cotton and have a lifetime of 5-40 minutes. Known for their flat bases and distinct outlines, fair weather cumulus exhibit only slight vertical growth, with the cloud tops designating the limit of the rising air. Given suitable conditions, however, harmless fair weather cumulus can later develop into towering cumulonimbus clouds associated with powerful thunderstorms.

[Image: fair weather cumulus field (77K)]
Photograph by: Holle

Fair weather cumulus are fueled by buoyant bubbles of air, or thermals, that rise upward from the earth's surface. As they rise, the water vapor within cools and condenses forming cloud droplets. Young fair weather cumulus have sharply defined edges and bases while the edges of older clouds appear more ragged, an artifact of cloud erosion. Evaporation along the cloud edges cools the surrounding air, making it heavier and producing sinking motion (or subsidence) outside the cloud.

[Image: another example of fair weather cumulus clouds (69K)]
Photograph by: Holle

The downward motion inhibits further convection and the growth of additional thermals from below, which is why fair weather cumulus typically have expanses of clear sky between them. Without a continued supply of rising air, the cloud begins to erode and eventually disappears.



Low-Level Clouds
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

cumulonimbus