WMOD00277

• Contract/Permit #: 14-06-D-6467
• Title: An Operational Adaptation Program for the Colorado River Basin
• Prepared By: Lewis O. Grant, Chappell, Crow, Mielke Jr., Rasmussen, Shobe, Stockwell, Wykstra
• Date: 10/1/1969
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

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TABLE II. --Estimate oJ scale changes during seeded periods with respect to
non-seeded periods as computed by three statistical methods. Scale changes
are shown as a function of the 700 mb mixing ratio.
With Controls Without Controls
Total Sample Scale Scale
Stratification Sample Size Change Change
(GM/KGM) Size Utilized Method (%) P- Value (0/0 ) P- Value
Climax I
O. 4 to < 1. 3 S 27 S 27 NP1 -28 . 171 < -50 .0392
NS 25 NS 25 NP2 < -50 .041 < -50 .0125
(S17,NS19) PAR -34 .115
1. 3 to < 2. 8 S 72 S 72 NPl +7 .305 +13 .261
NS 89 NS 89 NP2 +10 .258 +19 . 147
(S56, NS70) PAR +14 .166
2.8 to < 4. 6 S 21 S 21 NP1 +65 .071 +90 .138
NS 17 NS 17 NP2 +132 .255 +92 .206
(S17,NS13) PAR +35 .201
Climax II
O. 4 to < 1. 3 S 14 S 14 NP1 -32 .291 -22 .264
NS 11 ' NS 11 NP2 <-50 .074 <-50 .108
(S8, NS8) PAR -52 . 171
1. 3 to < 2. 8 S 36 S 36 NPl +23 . 187 +14 .298
NS 46 NS 46 NP2 -6 .409 +23 . 138
(S31, NS39) PAR +16 .224
2.8 to < 4.6 Sl1 Sl1 NP1 +25 . 181 +180 .152
NS 9 NS 9 NP2 +164 .106 +118 .305
(S10,NS6) PAR +13 .421

Wolf Creek Summit
O. 5 to < 1. 9 S 69 S 64 NPl -2 .480 -10 .409
NS 82 NS 79 NP2 -13 .323 -12 .334
(S34, NS45) PAR -9 .337
1. 9 to < 2. 8 S 59 S 50 NP1 +45 .050 +48 .111
NS 76 NS 74 NP2 +66 .0197 +41 .113
(S33, NS51) PAR +58 .0040
2.8 to < 5.2 S 36 S 33 NPl +57 .117 +165 .0183
NS 40 NS 28 NP2 +64 .127 +111 .053
(827. N825) PAR +54 .054

Again the consistency of the three
independent samples is apparent. Decreases in
snowfall are noted when seeding the colder
equivalent potential temperatures. At warmer
equivalent potential temperatures the seeding effect
reverses and snowfall increases when seeding the
warmest stratifications are substantial. These
increases are significant at the 5% level for most
tests in the Climax I and Wolf Creek I samples. Both
the two-sample Wilcoxon test and the two-sample
sum of squared ranks test indicate significance at
the 10/0 level for the Wolf Creek I sample when
analyzed without control.

c. Stability and baroclinic considerations.
The stability of the air mass approach-
ing the mountain barrier may influence the modifica-
! tion potential in complex ways. If the air mass is
convectively unstable precipitation may tend to con-
: centrate in relatively small cells and convective lines.

The stronger upward motirn s in these cells and lines
would result in high supply rates of cloud water in
localized areas. However, the stronger upward
motions would also probably result in higher cloud
tops. Since the number of effective ice nuclei
increases exponentially with cloud top height, while
tl::e need for additional ice nuclei grows only directly
with the upward speed, it is not obvicu s that modifi-
cation potential would be greater in uIlstable air
masses. On the other hand, if the convective
stability is quite low (near zero) and modification
potential exists for other reasons (lack of available
ice nuclei, for existing c1cu d conditions), the additional
release of latent heat resulting from seeding might
generate precipitation of a convective nature that
would not otherwise have occurred.

The static stability cf the air mass
also affects the nature of the laminar flow over the

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