WMOD00498

• Title: Some Climatological Characteristics of Seedable Upslope Cloud Systems in the High Plains
• Date: 3/1/1973
• Weather Modification - Doc Type: Report

The ice crystals required for the formation of natural precipi-
tation are produced when freezing or sublimation nuclei become ef-
fective at existing cloud temperatures, or when ice crystals are
introduced directly into the cloud volume from external sources (e.g.,
natural seeding from nearby clouds containing ice).
Supercooled shallow orographic cloud systems over the High Plains
often produce little or no precipitation. These clouds are thought to
produce little natural precipitation because of their shallowness, be-
cause of the low concentrations of natural ice nuclei active at pre-
vailing cloud temperatures, and because of the inefficiency of the

warm rain coalescence process.

On the other hand, the artificial production of significant pre-
cipitation from these cloud systems is favored by:
1. A temperature range where their precipitation potential
can be released artificially through seeding.
2. The high frequency of these clouds in the High Plains region,
3. The widespread nature of these cloud systems, and
4. Their relatively long duration.
Physical and numerical models have recently been developed for
cold orographic cloud systems in the western mountains of the U. S.
(e.g., Chappell, 1970; or Willis, 1970). These models, with some modifi-
cations, can be adapted to the shallow orographic cloud systems of the
High Plains.
Although the seedable cloud systems in the High Plains are similar

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in some respects to those on the western mountain ranges, some

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