WMOD00412

• Title: Final Report on Utah Cloud Seeding Experimentation Using Propane During the 2003/04 Winter
• Date: 3/1/2005
• State: UT
• Weather Modification - Doc Type: Report

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projects. That site, designated GTR, is the nearest suitable clearing to the exposed TAR positioned at the
head ofa major canyon. One gauge was planned to be no more than 2.4 km downwind of the TAR. Two
gauges were intended to be controls unaffected by seeding, near the heads of major canyons north and
south of the TAR.

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An additional site, previously used near the HAS, was outfitted with an old Universal gauge. It was
recognized that this gauge was marginal and that timing errors of 5 to 10 min could be expected.
Furthermore, SWE resolution was 0.005 inch at best even using an orifice with twice the area of the
standard 8-inch diameter. The location was near the HAS which needed frequent service visits so
operating the Universal gauge was a minor addition to the field program. However, this gauge was never
intended to be a primary control. An internal project document, "Overview and Update on Utah Propane
Seeding Experimentation - Winter of 2003/04" was completed on October 6,2003, prior to the field
experiment. The document stated the following concerning the near-HAS gauge. "It is anticipated that
even with an ETI (digitized) gauge, observations from this site would not be as well associated
(correlated) with the natural TAR gauge observations as the two plateau-top crosswind controls. That is,
this gauge site is not expected to provide as good a control as the others, but the data will be useful for
documenting natural snow showers approaching the experimental area."

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Considerable missing data resulted from use of the spring-wound chart drive in the Belfort gauge. A
series of major storm passages during late December 2003 caused postponement of service visits: to
several locations and the Universal gauge clock stopped for four days before it was visited. On another
occasion apparent failure to wind the clock resulted in a full week of missing data. In total, 16 EUs did
not have observations from this site. It was decided that there was little point in going through the tedious
process of manually reducing the chart data with so many missing cases. Furthermore, a number of charts
showed jerkiness in the pen trace likely caused by the oversized catch bucket rubbing against the: housing
wall. The bucket needed to be carefully centered to avoid this known problem. With these complications
and the relatively low elevation of the gauge, existing chart traces have not been reduced and the Belfort
gauge data have not been used for this project.

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5c. Locating Suitable Gauge Sites for the Randomized Experiment

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It was difficult and sometimes impossible to find suitable coniferous forest clearings at all locations
desired for gauges. Most of the Wasatch Plateau top is either wide open to the wind or has aspen
deciduous forest. Limited areas of conifer forest exist in some locations, especially on north and
northeast facing slopes. Two of the six locations which were to be provided with ETI gauges had been
successfully used in prior projects, and were known to have minimal wind effects. They were the primary
target gauge, GTR, and the GNO control gauge located 4.2 km north (crosswind) of the GTR (see Fig. 1.).
The other four proposed gauge sites had to be found and a few days were devoted to that purpose in early
September 2003. But finding sites which had adequate conifer forest and were practical to service during
winter proved more difficult than anticipated.

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The site nearest the seeding site, named GSC for Gauge Spring Creek, was an excellent location
protected both by dense conifer forest and by terrain. It was located near the bottom of a north f:acing
slope, where terrain became semi-level just above a creek bottom. An old jeep trail permitted
snowmobile access to within about 100 m of the gauge with snowshoe travel used beyond that point.
This location was believed to be very suitable for detection of possible seeding effects about midway
between the propane dispensers and the primary target gauge, GTR. Earlier work by Holroyd and Super
(1998) had speculated that such effects might exist, caused by aggregation of the numerous seeded ice
crystals and their scavenging (also aggregation) by natural snowflakes. They recommended that future
experimentation with propane seeding should attempt to document the fallout pattern with downwind
distance.

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