Geoscience Reference
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Figure 4.17. Wall clouds. (Top) May 26, 1978 in the Texas Panhandle with a developing tail
cloud feeding into the bottom of the wall cloud from the right; (bottom) May 26, 1991 in
southwest Kansas (as seen from the NOAA P-3 aircraft). A scud cloud is attaching itself to the
lowered cloud base above. (Wall clouds are also seen in Figures 4.6, 4.23, 4.25, and 6.2b, upper
right) (photographs by the author).
cooler, but more humid air from the adjacent FFD enters the updraft and lowers
the condensation level. There is some evidence that additional lowering of the
pressure is necessary to explain the observed lowering of the cloud base and that
it is a result of dynamic effects (i.e., the rotation associated with a mesocyclone).
The dynamical effects of vorticity on the perturbation pressure field will be
discussed subsequently. So, the appearance of a wall cloud is indicative of both an
updraft and rotation, though it is not clear which is the predominant charac-
teristic. Visually, one often sees wall clouds that are not rotating or are rotating
only very slowly.
Tornadoes, when they occur, are typically observed in the vicinity of the wall
cloud ( Figure 4.6 ). The RFD forms and impinges on the gust front that is located
 
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