WMOD00309

• Title: Applications of the Clark Model to Winter Storms Over the Wasatch Plateau
• Prepared For: Utah Department of Natural Resources Division of Water Resources
• Prepared By: James A. Heimbach, Jr.
• Date: 7/1/1993
• State: UT
• Weather Modification - Doc Type: Report

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1. Introduction
This report details the application of the Clark mesoscale model to the winter orographic weather
modification activities in the Wasatch Plateau of central Utah. The data used for model input were taken from the
early 1991 winter Utah/NOAA Cooperative Atmospheric Modification Research Program's field season which was
"piggy-backed" on the Utah operational program.
The principal goal of the modeling was to examine the transport and diffusion of seeding material released
from the Sanpete Valley and other points at higher elevations. Targeting of seeding material has been cited as a
significant problem in winter orographic weather modification projects (Reynolds, 1989; Super, 1990; Super and
Huggins, 1992). This issue was listed as the second goal of the research program designed for the cooperative
program (Utah Dept of Nat. Res., 1991).
In this report, the model was tested on two case studies using the results of tracer and meteorological data
taken during the early winter of 1991. The model was then applied to examine the wind flow about the Wasatch
Plateau, to model several release scenarios and to estimate the occurrence of liquid water. A large effort has been
made by the author to learn the Clark model and to adapt it to the Utah program, and this report represents an
interim summary of applications. This will be evident to the reader as the applications of the model evolve through
the two case studies presented
Section 2 of this report gives a description of the model, why it was selected. and some notes on its
application. Section 3 gives a description of the 1991 field season and the data applicable to the modeling efforts.
Some specialized analysis techniques are described in Section 4. Sections 5 and 6 detail modeling tests and results
for two case studies. A discussion of the results and recommended courses of action are given in Section 7.
2. Model Description
The three dimensional, time dependent numerical model by T. Clark and associates of the National Center
for Atmospheric Research (hereafter NCAR) was selected for application to the Utah program (Clark, 1977; Clark
and Farley, 1984; aark and Hall, 1991). The model is nonhydrostatic and anelastic which allows vertical
acceleration but eliminates acoustic-scale waves. The model uses spherical (non orthogonal) coordinates and the
vertical coordinates are terrain following such that the surface of the model follows the terrain and the top has a
constant level.
Interactive nested models can be run in parallel. This enables finer temporal and spatial resolutions within
the inner domain, and a broader upwind fetch can be econOlnically input to the model while applying the fine
resolution only to the innermost areas of interest. For the applications described herein, a three-domain setup was
applied. The final configuration used was a 9 km horizontal resolution for the outermost domain, a 3 km for the
middle, and a 1 km grid interval for the innermost domain. Earlier modeling work used three domains having
resolutions of 18,6, and 2 km. This setup was abandoned when it was obvious that 2 km was too coarse to model
the finer aspects of topographic forcing.

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