WMOD00416

• Title: Wintertime Cloud Systems Over the Rockies: Three Case Studies
• Date: 12/1/1980
• Weather Modification - Doc Type: Report

ABSTRACT OF THESIS
WINTERTIME CLOUD SYSTEMS OVER THE COLORADO ROCKIES: THREE CASE STUDIES

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This study focuses upon the mechanisms by which mountains and

synoptic weather systems interact to produce characteristic orographic

cloud systems. In each of the three case studies, a synoptic cloud

component, an orographic cloud component~, and a convective cloud compo-

nent were identified through the analysis of rawinsonde data, vertically

pointing radar data, and visual observations.

The follo"ring are considered to be the major findings of this

study: i) wintertime cloud systems over the Colorado Rockies form by

vertical velocity components which act on different size and time scales

(synoptic, orographic, and convective); i.i) at times, a fourth cloud

component, generated by the mesoscale structure of the synoptic distur-

bance (e.g., travelling gravity wave, moving convective bands, or organ-

ized convective lines, etc.) invigorates the entire cloud system,

iii) upwind blocking is very important to the orographic lift and the

lifted cloud system; iv) the deduced cloud is very sensitive to the

lifting model and the upwind profiles of temperature and moisture; and

v) synoptic storm tracks, travelling mesoscale phenomena, large scale

vorticity, moisture and temperature advection, synoptic and topographic

forcing of wind direction and speed, vertical structure of temperature

and moisture, cold air pooling, nocturnal valley inversions, blocking,

and stagnation all constitute controls on orographic cloud systems.

The timing and interaction of the above physical processes deter-

mine the formation and behavior of the cOTIlplete cloud system and define

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