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

Wall Clouds
 
> introduction
 
  beneath cb towers
 
  short-lived
 
  cyclic wall clouds
 
  with rotation

User Interface
 
  graphics
> text

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Wall Clouds
a lowering in the cloud base

Researchers have shown that wall clouds probably develop when some rain-cooled air is pulled upward, along with the more buoyant air, as the strengthening updraft attempts to replace ever-growing volumes of rising air. The rain-cooled air is very humid, and upon being lifted it quickly saturates to form the lowered cloud base. Thus, the wall and tail cloud probably develop sometime after an intense supercell or multicell storm begins to precipitate.

[Image: detached scud cloud (60K)]
Photograph by: Moller

Looking to the northwest, we see a detached scud cloud which had just emerged from the precipitation area and was moving rapidly southwestward (from right to left).

[Image: scud cloud in updraft (28K)]
Photograph by: Moller
About 5 minutes later, the scud cloud entered the updraft area and was lifted into the cloud base. This was the beginning of a wall and tail cloud that persisted for over 30 minutes.

Look closely at the center of the photo and near the north end of the tail cloud. A small, tornadic dust whirl is visible. This tornado circulation was relatively weak, but strong enough to overturn a mobile home. It was beneath the tail cloud and not the wall cloud! Events such as this have been observed more than once.

Numerous observations of wall clouds indicate these following items to be the main delineating characteristics between tornadic and non-tornadic wall clouds. Tornadic wall clouds usually persist for "tens of minutes" prior to tornadogenesis, whereas non-tornadic wall clouds often don't persist as long.

[Image: wall cloud characteristics (61K)]
Photograph by: Moller

Tornadic wall clouds exhibit rapid and even violent rotational and vertical (predominantly ascending) motions, with non-tornadic wall clouds having less dramatic motions. Finally, tornadic wall clouds are characterized by strong, warm inflow from the southeast and east, usually much stronger inflow than that with non-tornadic storms. We will discuss these characteristics in more detail.

In review, tornadic wall clouds are persistent over tens of minutes, have surface-based inflow, and exhibit rapid rotational and vertical motions. Next we will view several non-tornadic wall clouds and discuss their "tornadic short-comings."



Outflow Phenomena
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.

beneath CB towers