WMOD00598

• Contract/Permit #: NOAA/NA-81-RAC-00023
• Title: Evaluation of the Utah Operational Weather Modification Program - Final Report
• Date: 4/1/1982
• State: UT
• Weather Modification - Doc Type: Report

ABSTRACT

This study 1S an evaluation of a winter orographic cloud seeding
project in Utah. The evaluation is based upon both intensive field
measurements and historical records. For the field measurements,
ground and airborne data were collected during February and March, 1981
in the vicinity of the Tushar Mountains.

In evaluating the physical data three aspects are emphasized: the
dispersal of artificial ice nuclei. the distribution of supercooled
liquid water, and the growth and trajectories of precipitation.

Ground based measurements were made by K and X band radars, a dual
frequency microwave radiometer, a network of precipitation gages, an ice
nucleus counter, radiosonde/cloudsonde instruments and other standard

measurements.

Airborne data were obtained from the University of Washington's
cloud physics aircraft. Instrumentation consisted of five ice particle
probes (PMS), a Johnson-Williams and a Rosemount liquid water meter, an
ice nucleus counter, and other devices for reference such as altitude.
airspeed and position.

Results derived from these data indicate that ice nuclei released
------ -

from gro~!,d basecl_senerators did not generally reach cloud alt itudes in
--...----- -~- - - - -

sufficient quantity for effective nucleation and that the area covered by
---~--~ -- -

the weak upper edges of the plumes was limited to the order of about 10%
of the barrier.

Supercooled liquid water was fO\J.Jld_~~_~_ach,n_~__l!1aximum typically
just upwinci. of the barrier crest. Amounts found during the research
period were generally below that associated with seeding opportunities,
but meteorological conditions at the time were unfavorable for the
development of greater liquid water concentrations. Relationships of
liquid water to other meteorological conditions are also investigated.

i