DISCUSSION 
Fra. 1—Mean 700-mb contours for August 1936; note the great anticyclone over the Southern Plains 
and the companion cells over the Pacific and Atlantic 
building the upper level anti-cyclone, depending 
on the character of the surface. 
Figure 2 shows an isentropic analysis for this 
particular month (August 1986). This is a slop- 
ing surface of constant potential temperature 
(515° A) whose heights are given by the broken 
lines. Shown also are the circulating moist and 
dry tongues which are largely responsible for 
the outbreak or inhibition of showers. You will 
note in this great drought-producing cell that 
dry air is frequently flung from the westerlies 
over Canada, around the cell, finally entering 
into the central portion of this great anticy- 
clonic eddy. At the same time, this dry air moves 
from higher to lower elevations as it spins into 
the cell. The dry subsiding air inhibits the forma- 
tion of clouds. As a matter of fact, if Cumuli do 
form, when they penetrate this dry layer a sort 
of entrainment takes place, so that they are dis- 
sipated quickly, by the mixing with this dry air. 
Now, in the southern part of Illinois it is ex- 
tremely dry. There are deficits on the order of 
two to four inches in the Plains area of the 
United States. In some areas there is no rain at 
all, and the rain is confined to the left-hand por- 
tion of the moist tongue, where the air is to some 
extent forced up slope. A similar case was ob- 
) 
served during August 1955, and Figure 3 shows 
