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

TABLE 1. --Estimate of scale changes during seeded periods with r~spect to
non-seeded periods as computed by three statistical methods. Scale changes
are shown as a function of the 500 mb temperature.

{' ~ 1-

With Controls Without Controls
Total Sample Scale Scale
Stra tifica tion Sample' Size Change Change
(0 C) Size Utilized Method (%) P- Value (%) P- Value
Climax I
-35 thru -26 S 32 S 32 NPl -18 .109 -31 .0091
NS 34 NS 34 NP2 -8 .316 -22 .0329
(S28, NS34) PAR -23 .068
- 2 5 thru - 2 1 S 53 S 53 NPl -1 .472 -1 .492
NS 56 NS 56 NP2 -13 .309 -5 .390
(S43, NS43) PAR -7 .345
-20 thru -11 S 35 S 35 NPl +142 .041 +100 .076
NS 41 NS 41 NP2 +89 . 171 >+200 .024
(S19, NS25) PAR +102 .0023

S 18 S 18 NPl -28 .261 -46 .0039
NS 17 NS 17 NP2 -50 .152 -25 .0329
(S15, NSl 7) PAR -38 .059
S 23 S 23 NPl -1 ,.492 +6 .390
NS 32 NS 32 NP2 -30 .341 ~1 .496
(S20, NS26) PAR -5 .421
S 20 S 20 NPl >+200 .0301 >+200 .071
NS 17 NS 17 NP2 +176 .149 >+200 .042
(S14, NSI0) PAR +146 .0102

Climax II

-35 thru -26

-25 thru -21

-20 thru -11

Wolf Creek Summit
-35 thru -24 S 43 S 42 NPl -15 .218 -15 .264
NS 61 NS 61 NP2 -25 .071 -22 .164
(S3l, NS48) PAR -9 .302
S 57 S 47 NPl +49 .053 +22 .233
-23 thru -20
NS 68 NS 66 NP2 +62 .044 +23 .192
(S32, NS45) PAR +43 .0384
S 64 S 58 NPl +95 .068 >+200 .0037
-1 9 thru - 11
NS 69 NS 54 NP2 +200 .0207 >+200 .0125
(S3l,N328) PAR +81 .0113

sample. Both the mois t and intermediate categories
of the Wolf Creek I sample show snowfall increases
when seeded that are significant at about the 5%
level.

It appears that the vertical gradient
of potential condensate computed for the 700-500 mb
layer s tra tifies the seeding effects somewhat better.
Snowfall decreases, when seeding cases in the driest
cateQ"ory, are significant at the 1%
for the Climax I sample and at the 5% level for the
C 1 i m a x II sam p 1 e. All th r e e samples
indicate snowfall increases when seeding the more
moist events. The two-sample sum of squared
ranks test is significant at the 1 % level for the Wolf
Creek sample.

These results are consistent with the
model presented. As the rate of cloud water supplied

increases, the concentration of ice crystals needed to
convert the cloud water to ice at the new rate also
increases if other variables remain constant. The
results in Table II and Table III indicate that cloud
water is frequently supplied at a rate in the Climax
and Wolf Creek Pass areas, that is in excess of the
natural capacity of the cloud system to convert to ice
form. The effect of seeding under these conditions
s'hould be to increase the rate at which the cloud
water may be extracted resulting in more snowfall on
the mountain barrier.

The equivalent potential temperature
evaluated near or just below cloud base identifies the
pseudoadiabatic process curve of rising. cloud parcels.
It combines the moisture and temperature character-
istics of the air mass approaching the mountain barrier
into a single parameter. Table IV shows the distribu-
tion of seeding effects as a functi01 of the 700 mb
equivalent potential temperature.

16