WMOD00416

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

CHAPTER I INTRODUCTION

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The formation of many orographic cloud systems can be attributed

to the passage of synoptic scale migratory waves. These atmospheric

disturbances provide the moisture and circulation, when sufficiently

forced by the mountains, to form this type of cloud system. This is

especially true of continental orographic cloud systems which play a

significant role in establishing the winter snowpack in the Colorado
Rocky Mountain region.

Precipitation in mountainous terraUl can be thought of as being

made up of three components: (a) the s~loptic precipitation component,

(b) the orographic precipitation component, and (c) the convective pre-

cipitation component. These three precipitation components are direct-

ly related to the vertical motion fields associated, respectively, with

migratory waves, terrain lifting, and the local release of convective

instability (Elliott, 1966; Rhea, 1972; Rhea, 1978). Visual observa-

tions by Marwitz (1974), radar observations by Furman (1967), satellite

observations by Reynolds and Morris (1978) and Morris (1979), and pre-

cipitation network analysis by Elliott and Hovind (1964) and Elliott

and Schaffer (1962), point to the existence of precipitation components

associated with each of these mechanisms.

The economical importance of the winter snowpack to the Colorado

Rocky Hountain region (e.g., ski industry, avalanche prediction, snow

removal) calls for an understanding of how synoptic, migratory waves

form different types of precipitating orographic cloud systems. This

can be achieved by recognizing the fact that the characteristics of each

cloud system are determined by a combination of the components as the

synoptic scale disturbance passes.

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