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

Severe Storms
 
  introduction
 
  dangers of t-storms
 
  types of t-storms
 
> tstorm components
 
  tornadoes
 
  modeling

Tstorm Components
 
  introduction
 
  updrafts/downdrafts
 
  wind shear
 
> outflow phenomena
 
  wall clouds

Outflow Phenomena
 
  introduction
 
> gust fronts
 
  microbursts
 
  scud clouds, virga
 
  rain foot, dust foot

gust fronts
 
  introduction
 
> visual clues
 
  more clues

User Interface
 
  graphics
> text

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Visual Clues to Gust Fronts
cloud lowering slopes downward and away from rain area

This is the first of four photographs of an approaching thunderstorm to help visualize the difference between gust front outflow "push" and wall cloud inflow "pull." To the distant west-southwest, note the suspicious cloud lowering at the south flank of an isolated severe thunderstorm. Is it a wall cloud or a portion of a shelf cloud?

[Image: shelf cloud (49K)]
Photograph by: Doswell

A subtle, but important clue is that the lowering slopes downward away from the rain area, rather than into the rain. This is the slope that a shelf cloud usually takes. As cold air is "pushed" out of the precipitation area by the downdraft, warm air slides up and over the gust front forming the concave-shaped shelf cloud. Within 20 minutes, the storm continued to approach. The ragged shelf structures has the same tilt, and although it is a bit easier to identify, there is still some question as to its nature.

[Image: shelf cloud pushed outward from precip (52K)]
Photograph by: Doswell

Another important clue is to discern whether or not the cloud element in question remains in one spot relative to the precipitation area, or moves away from the precipitation. When it moves away, as this cloud has, it signifies "push" and shelf cloud-producing outflow. Observe carefully, for there are signatures of strong outflow winds (a steep-sloped rain foot and a small gustnado). The storm was producing 70 MPH winds at this time.



introduction
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.

more clues