WMOD00416

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

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(The CaSE II experimental period happened to be exceptionally dry for

the Park Range area.) It becomes obvious that the degree and frequency

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of instability experienced over the Park Range of Colorado is not excep-

tiona1ly large and since the layer ana1ys,is method is more sensitive to

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this degree of instability, the layer potential instability analysis,

rather than the parcel method, is best suited for this area.1

In order to analyze for the convective cloud compon~nts present

within each sounding of the case studies, equivalent potential tempera-

ture (8 ) was plotted as a function of height and the convective poten-
e

tia1 instability was defined in the fo11o~ng way:

A.

Potential instability base equals the point at which the 8
e

profile begins to decrease with height. (PIB)

B. Potential instability top equals the point at which the 8
e

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profile again equals the e value at the layer base. (PIT)
e

The layer is lifted according to the simple model used to define

the composite cloud (see Cloud Analysis section 2.3). The convective

cloud component generated by the instability is determined from the

following:

C. Convective instability base was taken as the LCL of the poten-

tia1 instability base. (CIB)

D. Convective instability top was taken as the potential instabi1-

ity top if the top of the layer became saturated with respect to water

or it was equal to the cloud top if the water saturated top was below

the potential instability top. (CIT)

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1This general lack of extensive instability has been expected because
winter storms which favor precipitation over the Park Range are gener-
ated by modified maritime polar airmasses (Rhea, et a1., 1969, pp.
108-109).

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