WMOD00235

• Applicant: Western Kansas Groundwater Management
• Project Name: Cloud Seeding
• Date: 4/15/1986
• Weather Modification - Doc Type: Report

poducing most of the rain and hail are: (1) the air-mass,(2) the
multiple cell varieties, and (3) the squall line.

Air-mass storms begin as isolated cloud systems that develop a
well-organized cloud base with an easily delineated inflow area
protruding below the general base of the cloud. Specific claud
movements may vary widely due to individual cloud heights attained
because windspeed and direction often varies considerably with height
Terrain effects probably play some role despite the relative flatness
of Kansas.

If one draws a line throLlgh the precipitation area of an air-mass
storm in the direction of storm movement, then draws another line at
right angles ~~ it in the center of the precipitation area, updrafts
found upwind in the cloud are termed "trailing'J or "back side";
whereas, downwind at1ead of the line it's termed "front side!'.
Although updrafts are sometimes found on the front side portion of an
air-mass storm, it is not considered to be of primary importance to
the formation of precipitation. Normally, the important updrafts for
these storms are found below cloud base and at some distance behind
the precipitation area, usually along the trailing edge of the storm.

Air-mass storms often continue to develop into a line of storms
COlltaining multiple cells that eventually exhibit some squall line
characteristics. As such, stol~ms sometimes grow into a multi-cellular
line with multiple shifting updraft areas that often make cloud base
treatment difficult. The location of the important updrafts on these
types of cloud systems are usually} but not always, found along a line
in the frontal portion and call be a few miles to many miles in length.
A typical air-mass storm and the methods emploYGd to seed it a~e shown
in Figure 3.

There is one ottler system that appears to have important
pootential in producing precipitation in Kansas: this is the multiple
cell convective system. This st.arts as a cluster of slnall, weak
clouds developirlg within a small area. If one, or more, of the clouds
is able to grow sufficiently! it captures (or merges) witt1 one of the
others and intensifies. Further intensification allows the storm to
capture other smaller ones and further increase in intensification.
These storms will produce precipitation over large areas and persist
longer than the "average" thunderstorm. Updrafts initially found on
the "best" storm within the clustel~ are often embedded or difficult to
locate, however, once the storm grows to sufficient size, updrafts
gerlerally organize better. The case study of AlAgust 24, 1986
presented in this report deals with just this type of clo~j.

The cloud system known as the squall line is an organized line of
CUMulonimbus cloud5 with the important updraft area found along the
leading edge of the line of storms. Vertical updraft velocities can
e;(ceed 2000 feet per minute. Roll clouds and updraft I'SClAd" clouds
are often visible almost to the ground. Severe turbulence can be
associated with this inflow area althougt1 it tends to decrease rapidly
from the leading edge of the l.irle. Si.gnificant updrafts are seldom
fOl~nd along the trailing edges of squall lines except occasionally at
the end of the line or at significant break:s within the line.

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