WW2010
University of Illinois

WW2010
 
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Online Guides
 
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> 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

Weather Forecasting
 
  introduction
 
  methods
 
> surface features
 
  temperatures
 
  precipitation

Surface Features
 
  anticyclones
 
  cyclones
 
  cold fronts
 
  warm fronts
 
  stationary fronts
 
> occluded fronts
 
  dry lines

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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Occluded Fronts
when a cold front catches a warm front

An occluded front develops when a cold front catches a warm front. For a maturing cyclone, a warm front is progressing northward ahead of the storm center while a cold front is sweeping southeastward. The cool air mass north of the warm front is already in place.

As the storm intensifies, the cold front rotates around the storm and catches the warm front. This forms an occluded front, which is the boundary that separates the new cold air mass (to the west) from the older cool air mass already in place north of the warm front. Symbolically, an occluded front is represented by a solid line with alternating triangles and circles pointing the direction the front is moving. On colored weather maps, an occluded front is drawn with a solid purple line.

Ahead of the occluded front, temperatures were reported in the low 40's, while temperaturesbehind the front were in the 20's and 30's. The air mass behind the front is also drier as shown by the lower dew points. Wind direction reports to the east of the front are from the east or southeast, while winds behind the front are from the west or southwest. Convergence of the easterly winds ahead of the occluded front and the westerly winds behind it can result in showers of rain or snow.

[Image: occluded front on weather map (26K)]
Image by: WXP Purdue

With the passage of an occluded front, weather conditions will likely turn from cool to cold. Winds will swing around from easterly to westerly or southwesterly with rain or snow showers possible, (depending upon how cold the temperatures are).



stationary fronts
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.

dry lines