WW2010
University of Illinois

WW2010
 
  welcome
 
> online guides
 
  archives
 
  educational cd-rom
 
  current weather
 
  about ww2010
 
  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

Weather Forecasting
 
  introduction
 
  methods
 
  surface features
 
  temperatures
 
> precipitation

Precipitation
 
  frontal lifting
 
  moisture
 
> rain or snow

User Interface
 
  graphics
> text

NOTE: We've guessed that you're not using a client that supports colored tables and have tried to compensate. Low graphics mode looks much better on clients that do... we recommend switching to Netscape 3.0 or Microsoft Internet Explorer.
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Rain or Snow?
dependent upon temperature

Most precipitation that reaches the ground actually begins as snow high in the atmosphere. These snow flakes develop somewhere above the freezing level where the air temperature is less than 32 F (the dashed blue line), and begin to fall toward the earth as snow. If ground temperature is above 32 F, the freezing level must be located somewhere above the ground. The falling snow passes through the freezing level into the warmer air, where it melts and changes to rain before reaching the ground.


When the air temperature at the ground is less than 32 F, the precipitation begins falling as snow from the clouds.


Since it is falling into cold air, the snow does not melt on the way down and reaches the ground as snow. This is why cold air is important for there to be snow.


Once in a while, a very thin layer of warm air is found near the surface and temperatures may be several degrees above freezing. However, since the layer of warm air is so shallow, the snow reaches the ground in tact before it has a chance to melt and become rain. This is how snow falls when the surface temperatures are above freezing.

Forecast Tip:
When forecasting precipitation type, if temperatures are expected to be above freezing, then rain is most likely. If temperatures are expected to be below freezing, then forecast for snow.



moisture
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.

Remote Sensing