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

Forecasting
 
  precipitation type
 
  classic sounding
 
> swrp sounding

User Interface
 
  graphics
> text

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SWRP Sounding
supercooled warm-rain process

Below is a sounding that typically results in freezing rain through Supercooled Warm Rain Processes (SWRP). Throughout the sounding profile, the temperature never exceeds 0C (32F). The process begins as supercooled raindrops grow by collision and coalescence, and since the temperature throughout the cloud is warmer than about -10C, the cloud is generally free of ice crystals. This is important because if ice crystals were present, the cloud drops would instead grow by ice crystal processes, producing snow and not freezing rain. Winds are typically out of the west or northwest at the surface, veering to the southwest in middle and upper levels.

In the second sounding, the temperature exceeds 0C (32F) above the cloud. This type of sounding is commonly observed in the Southern Plains where very warm mid-level air from the Mexican plateau overrides colder air in the surface layers. Winds at the surface are usually from the east or southeast and veer around to the southwest or west in middle and upper levels.

The best way to forecast freezing rain is to examine forecast model soundings for profiles similar to the ones described in this module. One web site providing these products is the Northern Illinois University's Storm Machine. One can choose the city and model and receive the appropriate forecast soundings, from which a forecast can be made about when and where freezing rain will occur.



classic sounding
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.

Precipitation