WMOD00079

• Contract/Permit #: #98-1
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 1/1/1998
• Weather Modification - Doc Type: Report

Under some conditions rainfall augmentation over large areas have been produced by seeding
atop the leading edge of a gust front as air is lifted over it which causes only weak cumuliform clouds
to form, Updrafts found above gust fronts have wide variability---from 100 - 200 feet per minute to
a more norma11000 - 1500 feet per minute, or more. If this particular condition occurs at night with
little threat of hail developing from new storm growth and weak updrafts are prevalent, rainfall
stimulation seeding can be highly productive over large areas. In such cases the cloud's microphysical
characteristics are attempted to be altered by seeding. It's likely under these conditions the dynamic
effect is markedly changed, whereas, the "static" seeding effect is being achieved. It is likely that
hygroscopic seeding above a gust front may also produce good results, however, it has not been
tested on this program yet under the circumstances given.

There is another form of cloud system which has important seeding potential, on occasion, for
producing precipitation in Kansas: the multiple-celled-convective system. This starts as a cluster of
small, weak air-mass clouds developing within a relatively small area---typically 10 - 30 miles in
diameter. If one, or more, ciouds can grow sufficiently to merge with another, the resulting merged
cloud tends to continue growing, thereby promoting further cloud mergers which further increases
both cloud volume and intensity. SU(;h cloud systems are capable of eventually producing precipitation
over large areas and persisting much longer than they normally would, otherwise. Updrafts initially
found within such a cluster of cells are often embedded and difficult to locate, however, once such a
system grows to a certain size, updrafts generally organize better and the cloud system becomes easier
to continue seeding. Under natural conditions, many times these ani regions become the "first echo"
development"seen on radar. First echoes have a high correlation to being the day's first severe storm.

Most of the important research on the dynamics of the multiple-celled-convective system was
done years earlier in West-Central Texas. By the same token, earlier radar studies from 1972 to 1974
of Northwest Kansas clouds found this area was a fertile region for these smaller cell clusters to
develop. Comparisons of data seem to suggest Western Kansas may, be even better than in that Texas
where the most extensive research has been conducted. In the early years scant attention was paid to
those weak-appearing multiple-celled cloud clusters until one of them had grown much larger. If some
of those systerns had been treated early, instead of waiting to see whether they grew and became much
larger, more frequent success for rain stimulation and/or hail suppression probably would have
occurred. Today, however, we anticipate the development of these smaller cloud clusters and realize
they may have the potential to become "targets of opportunity" to produce rainfall over large areas
as well as regions of preferred hail development. When observed, the attempt must be made to begin
seeding them as early as possible in hopes of catching the "window of opportunity" for dynamic
seeding effect discussed earlier. Spectacular results appear to have occurred on some past occasions
. from seeding such cloud systems.

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