WMOD00034

• Contract/Permit #: #94-6
• Applicant: North American Weather
• Project Name: Willow Creek Basin
• Date: 11/1/1994
• Weather Modification - Doc Type: Report

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The linear regression equation developed from the historical relationship between
the control and target groups is as follows:

yc= ,97 + .53Xo

(4)

where y c is the calculated average target precipitation (inches) and Xo is the five

station control average observed precipitation (inches) for the December through April
period.

5.3.4 Evaluation Results (PreciDitation)

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When the observed average control precipitation (18.75 inches) for the December
1994 through April, 1995 period was inserted in equation (4), the most probable average
target area precipitation was calculated to be 10.82 inches. The actual observed average
precipitation for the two gauges in the target group was 12.85 inches. This is an average
of 2.03 inches more precipitation observed in the target area than predicted, and
compares to the .79 inch excess indicated for the April 1 snow water content in the
snowpack evaluation. From equation (2) the ratio of target area observed to calculated
precipitation for 1995 is 1.188 or from (3) 18.8 percent more than predicted by the
regression equation.

The precipitation regression was based on a 32 year historical record, from 1961
through 1992. During this period the control sites have averaged 17.18 inches during
each December through April period, while the target area sites have averaged 10.00
inches during the same periods. From December 1994 through April 1995 the control
sites received 18.75 inches (l09 percent of the 32 year nonnal), while the target area
gauges averaged 129 percent of nonnal. This is similar to the April 1, 1994 snowpack
averages, which were 131 percent of the average in the control, and U8 percent of
nonnal in the target.

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