WMOD00416

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

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criteria will insure that blocking will be accounted for and that the

orographic lift will be reduced by an appropriate amount. (If the low-

est atmospheric layers are blocked from ascending the barrier, the up-

wind airflow will be exposed to a lift that will be less than the topo-

graphical height of the barrier. See also Marwitz, 1980.)

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2.3 Cloud Analysis
In order to accurately reconstruct each storm event, it becomes

necessary to define the three proposed components of the cloud system.

This includes the upwind portion of the system which is not orographi-

cally lifted (the synoptic component), the topographically forced por-

tion of the cloud system (the orographic component), and the portion of

the cloud system in which convective motions are expected to occur by

the release of potential convective instability (the convective compo-

nent). The first two components must be defined from rawinsonde cloud

base and cloud top criteria, while the convective component is defined

from a stability analysis performed upon the rawinsonde data and the

lifting of the sounding (see Stability Analysis section 2.1).

There are many ways to define a cloud from rawinsonde data. Water

saturation, ice saturation, an arbitrarily defined dew point depression,

or an arbitrarily defined relative humidity, are a few of the criteria

used (Dept. of the Air Force, 1969; Elliott, 1969; Rhea, 1972; Dumont,

et a1., 1974; Dumont, 1975; Marwitz, et a1., 1976; Vardiman, ~ al.,

1976; Rhea, 1978). Depending on which criteria is used, a cloud top

may vary by as much as 20 kPa! The upwind synoptic component of the

cloud system will be defined as that portion of the sounding which is

saturated with respect to ice. This criteria will be used with the

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