WMOD00071

• Applicant: Western Weather Consultants
• Project Name: Vail Pass
• Date: 11/1/1984
• Weather Modification - Doc Type: Application

Appendix to Question No. 11

F"r~U'''''

"t('f! P~<!{l4c<;;
C",...,...S.-; b,

Lf "Tt.o::. r...../'~.h (..{ S"........ E.....l...,.c~,..,_-.-..;...
L~<- L.;. ,-.)~;~Le.:.K.~r 19"7-Y

The comput~tions of increas~s due to seeding ~ere examined
to see if the augmented amount tended to be reratively laq,c when the
natural snowlal1 was large, or conversely, This set of data is sho~n 1n
Figure 14(a). Although lil1l1ted in size, the s311lple indicates that there
1, a positive relationshlp. The natural snowfall snd amounts produced by
.~edLnC bave a linear cor(relation of 0.6. The increases were also cQlllputed
.5 a percentage of the natural snowfall. Flgure 14(b) shows that this pcr-
centa&e'1s not dependent on natural snowfall. Therefore. the same percent-
.~e 500_ au~entation may be used in both low and hi~h years of natural
ano....ta 11 ,

We may SUllunarize the discussion of snowfall augmentation

as follows:

(1) The IIlOst probable increase in snowfall at elevations
above 8000 it that Can be realized by sccding is in
the range from IlpproxilllOl.tely 20 to 25 percent, as
an average figure for the basin OVer a period of at
least several years, In our judgment the chance
that subsequent, long.term data will sbow that this
figure is less than 10 percent or greater 'than 3S
percent Is less than one in ten. This assumes that
state of the art cloud seeding 15 done in an optlaal
aanner. If it is not done optimally then the percent
increase in snowfall will be less.

(2) The increases are produced ~inly by changing hours
in which little snowfall 'QuId have occurred
naturally into hours of slgnilic:lnt snowfall. As
a result, the days with relatively lar~e amounts or
snow (e.g., amounts greater than One half inch of
water equivalent) w111 be olle and a h3.1f to twice as
frequent (see Figure 11).

(3) The proportional increase in snowfall produced by
$eedin~ ~ill be the same whether the season 1s wet
or dry.

(4) The kernel of the effect of seeding is that it will
make the Snowfall amounts of the target area simiiar
to the natural snowfall that exists at elevations
500 to 1000 It higher in the mountains.

As a simple but reasonably accurate rule for computlng
!ugmented seasonal sno_fall, one may apply percentage increases to the
~~~.~nal snowhll overages. HO\loever. the percentage inCreOlses that
should be applied to the different localities are not well known at this
time. In the light of dlscussions with Professor Grant and our computa-
tions given earlier, we selected the percentage increases shown in
Fii;ure i5 liS the IllOst prObable esltmates. These percentage Increases
Were then applled to the seasonal snowfall of FIgure 7 to obtain the
average snowfall (water equivalent) that would be produced by seeding
methods that can be implemented within the next five YC8rs (F'lgure 16).
This map. and the two that follow, were used cxtcnslvely in the study to
estimate hydrologi.c confH t10ns and the et'fects on ecological, social, and
econOmiC systems; theretore. they arc c;"ttrcllIely important.