WW2010
University of Illinois

WW2010
 
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Online Guides
 
  introduction
 
> meteorology
 
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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

Precipitation
 
  introduction
 
  rain and hail
 
> freezing rain
 
  sleet
 
  snow

Freezing Rain
 
  definition
 
  dangers
 
  regions
 
> processes
 
  conditions
 
  forecasting

processes
 
> ice-crystal
 
  warm-rain

User Interface
 
  graphics
> text

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Ice-Crystal Mechanisms
the formation of freezing rain

Freezing rain can develop either through ice crystal processes or supercooled warm-rain processes. Ice crystals high in the atmosphere grow by collecting water vapor molecules, which are sometimes supplied by microscopic evaporating cloud droplets. In the figure below, the blue line represents the temperature of the atmosphere and the black line represents the 0C (32F) isotherm (a line of equal temperature). When the blue line is to the right of the black line, the atmosphere is warmer than 0C and when the blue line is to the left, the atmosphere is colder than 0C.

As the snow falls, it encounters a layer of warm air where snow and ice particles completely melt and collapse into raindrops.

As the raindrops approach the ground, they encounter a layer of cold air and cool to temperatures below 0C. However, since the cold layer is so shallow, the drops themselves do not freeze, a phenomena called supercooling (or forming "supercooled raindrops"). The supercooled raindrops are raindrops that are colder than 0C and freeze on contact when they strike the ground.



Freezing Rain
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.

warm-rain