WMOD00299

• Title: Physical Structure of Northern Colorado River Basin Cloud Systems
• Date: 9/1/1985
• State: CO
• Weather Modification - Doc Type: Report

20

I
I
I
I
I
I
I
1
I'
I
I
1
1
I
I
I
I
I
I

(Hill, 1980) in the northern Wasatch Mountains of Utah during the late
1970's. Hill \found that the presence of supercooled liquid water in
cloud systems over the northern Wasatch was primarily related to the
vertioal velooity generated by flow deflection over the barrier. This
vertical velocity was found to be proportional to the cross-barrier wind
speed. The magnitude of the liquid water in the cloud was also modified
by the crystal concentrations present in the cloud, as indicated by the
precipitation rate. Higher precipitation rates were associated with
colder cloud top temperatures. Data presented by Hill also showed that
aircraft icing was approximately proportional to oross-barrier wind
speed. Using these results, Hill suggested a seeding hypothesis based on
oross-barrier wind speed and cloud top temperature criteria.
Marwitz and Stewart (1978) reported ,the results of four air,craft
flights over the northern Wasatch and Uinta Ranges during the spring of
1978. They found that concentrations of supercooled water at flight
levels exceeded 0.2 gm-3 only in convective elements and that regions of
high liquid water concentrations contained few ice crystals. Clouds
over the Uinta Range during the study were found to be devoid of liquid
water. These clouds had significant amounts of ice crystals, mostly
unrimed.

(8) Utah Federal-State CooD~rative Project
The Utah Federal-State Program is an ongoing program or research
"piggy-backed" on an operational program in the southern Wasatch
Mountains or Utah. Preliminary resu~ts of this program are oontained in
project reports by Hill (1982b) and ~ong (1984). The emphasis or th.s.
programs has been the study of ice nuclei dispersion and supercooled
liqui.d water distributions. Studies in this program are not
. I .- 'I -:.- I .,,, ". ,.'.