WMOD00259

• Applicant: Western Kansas Groundwater Management
• Project Name: Western Kansas Weather Modification Program
• Date: 1/1/1999
• Weather Modification - Doc Type: Report

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whenever possible if it appears its implementation would enhance our overall operational
capability while keeping costs at reasonable levels.

The cloud systems listed below, and variations of them, are most responsible for
producing rain and hail in Western Kansas:

(1) the air-mass storm complex

(2) multiple-celled storms

(3) the squall line

Air-mass storms often become complex after starting out as an isolated cloud system
with a well-organized Cloud base and its new growth updraft area usually visible somewhere
around its base. Multiple cloud turrets often develop around the initial "parent" storm and
subsequent storm movements can become erratic depending upon several factors such as its
severity, terrain effects, dynamic factors within the storm, cloud height, variability of wind speed
and direction with height plus the blocking of steering winds caused by large upwind cloud
systems. .

Air-mass storm complexes often transition into a large, multi-celled systems. Fig. 2
shows a "classic" storm with new growth on its upwind (left) side. Updrafts found upwind of a
storm's direction of movement are termed "trailing" or "back"side; whereas, the downwind front
side is its leading side. Most often, updrafts pertinent to the hail process are found along its
trailing edge below cloud base at some distance behind the precipitation.

Air-mass storms can transition into a line of storms containing multiple cells showing
characteristics more similar to those of a small squall line. During the gradual development of
these multi-cellular lines, cloud base updrafts frequently shift around although they are still found
near some of the individual cell elements comprising it making proper seeding treatment quite
difficult at times.

The updraft locations important to the hail process on these cloud systems are along a line
on its front side, running from a few miles to many miles in length. Other times, the best seeding
area may be around only one end of the line. Multi-celled lines may also appear as a remnant of a
weakened squall line or as part of a line of storms associated with fronts, surface troughs and
thunderstorm outflows. .

Under some conditions multi-celled storms may become very large, developing several
new growth areas simultaneously with distinct "cores" growing embedded in and around the
periphery of the cloud boundary while the cloud system is in transition from being a relatively
small severe storm into a large supercell. One characteristic of a supercell is that at some point it
exhibits a "right-turning" motion relative to the direction of the mean steering wind. Supercells

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