WMOD00311 ‎(2)‎

• Title: Climatologies and Intercomparisons of Rawinsonde Data Collected During Winter Storm Periods in Utah
• Date: 8/1/1980
• State: UT
• Weather Modification - Doc Type: Report

available for conversion to precipi ta tion, 3) the ice nuclei
supply available for precipi ta tion . ini tia tion, and, 4) the
time available for nucleation growth and fallout of precipi ta tion.

Various physical and empirical measures of these four
basic categories were accumulated for the six project areas
and subsequently related to precipitation and ultimatel~r the
effects of seeding. Seeding effects were generalized to cover
the data from the six individual projects in terms of multi-par-
ameter "seeding windows" - derived primarily from rawinsonde
information normally collected just upwind of the associated
target areas. These windows were developed to identify positive
and nega ti ve seeding effects for three general regions over
a mountain barrier - upwind, crest, 'and downwind.

Consideration of these physical categories in making
opera tional seeding decisions is not a new concept.. However,
the study provided tentative bounds for selected air mass
parameters and' combinations thereof that appeared to maximize
the seeding effect in the barrier crest area.

The bounds suggested for the air mass parameters in the
above study, although tentative, have been used as guidance
in making operational seeding decisions on the Utah seeding
program. For item one, the low level stability must allow
the vertical mixing of the ground released nuclei (silver
iodide particles) into suitable clouds.

For item two, a minimum cloud base water content was
suggested. This restriction based upon a statistical analysis
of the six research programs can be interpreted in a physical
sense as a requirement for fairly moist cloud conditions before
seeding can produce a posi ti ve effect. For the Utah project
2-5

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