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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all good and fair cases while excluding only 3 poor cases. The HAS wind direction does not appear to be
particularly powerful in excluding poor targeting for the range of data available during the 1995/96
experiments. Ignoring the 324 deg outlier that range was 152 to 271 deg. Moreover, it is possible that
some of the poor targeting had nothing to do with the wind but was caused by AgI generator problems.
This possibility would seem most likely for the approximately 3 min bums for the beginning and ending
AgI "tags" used for propane seeding experiments. It is sometimes difficult to establish a stable output in
such a brief time.

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The prior data do indicate that HAS-released plumes should routinely pass by the TAR for HAS wind
directions between about 170 to 270 deg. This finding removes much of the uncertainty concerning
targeting which has been inherent in most experiments and operational projects. It is important to have
these results, from earlier plume tracing studies, when applying statistical analyses to the 2003/04
randomized experiment. Targeting can be considered highly probable for the 170 to 270 deg HAS wind
direction range. Targeting for experimental units with winds outside that range should be considered
suspect.

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As will be shown in Sec. 6c2, 29 of the final 98 experimental units (30%) from the 2003/04 program
had winds greater than 270 deg, specifically within the range 278 through 325 deg. Only two cases with a
northerly component exist in the 1994/95 and 1995/96 data set, primarily because experiments were
attempted only when HAS winds were within the southwest quadrant. Examination of the topography
suggested targeting at the TAR was unlikely if winds had a northerly component, and that was borne out
by observations.

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Frequency of Targeting
Ratings by Tar Wind Dlr.
Sectors for 1994/95 and
1995196 Winters.
en 20 24 Good = Black
Cl 20 Fair = Gray
c:
....
III 15 Poor = White
lr.
Cl
c:
.... 16
G.l
El
~
C".I
.e
.l!:I 12
c:
~
'C
G.l
Q.
~
- 8
0
:n
.0
E
::l
Z
4

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240

245

250 255 260 265
Mean TAR Wind Direction (deg true)

270

275

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Fig. 7. Frequency distribution of TAR wind directions for 59 experiments with good, fair or poor TAR targeting
conducted during the winters of 1994/95 and 1995/96.

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