WMOD00444

• Title: Evaluation of Idaho's 1992-1993 Winter Cloud Seeding Program
• Date: 10/1/1993
• Weather Modification - Doc Type: Report

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Although seeding continued into mid- or late April in the three projects, the seasonal
snowpack is known to reach its maximum on or soon after April 1 in most years. Using
measurements after April 1 will result in lower correlation coefficients between many
snowpack measurement locations because ofthe added variability ("variance") caused by snow
melt at some sites during some years. Consequently, April 1 observations were mainly used
in the target-control evaluations.

Any sites lower than 6000 feet elevation (all elevations are above mean sea level) were
excluded because of the possibility of melting significantly affecting the measurements. Some
of these sites had frequent zero SWE readings by April 1. Finally, three sites that were
aerial markers were excluded. Such sites have only depth readings. Their SWE is estimated
by using density observations from snow courses in the vicinity. SWE observations from the
three aerial marker sites were not highly associated with nearby snow course or pillow
observations. A final list of 76 acceptable sites was prepared of all snowpack measurement
sites that met the stated criteria for April 1 observations, as given in appendix A.

6. EVALUATION OF THE BOISE TARGET AREA

6.1 Control Sites

Table 1 lists the available sites for the Boise projeet in the following order: target sites,
control sites west or northwest of the target, control sites southwest of the target, and sites
within 25 miles east (generally downwind) of the target. The SCS site name and
identification number is given for each location along with its elevation (feet), latitude
(degrees-minutes) and longitude (degrees-minutes). The number to the left of the site name
is the alphabetical rank out of all 76 sites used in analysis of all three projects, with the
Idaho sites listed first, followed by Montana and Wyoming sites. The last four sites are Idaho
control sites that were added late in the analysis process. Sites will be referred to by the
number left of their name.

Figure 2 shows the locations of the SWE measurement sites listed in table 1. Each SWE
measurement site is shown by a star with a number next to it corresponding to table 1 and
appendix A. The boundary of the target area and thE! locations of the 19 AgI generators are
shown as provided by NAWC. The 7000-foot contour is shown within the target area where
the terrain elevation generally increases eastward.

Some of the snow measurement sites require clarification. Site 8 lies immediately west of
the NAWC designated target area and might be sub~ect to contamination by seeding with
some wind directions. Similarly, site 3 lies due north of the center of the target area and
might be affected by seeding with southerly flow. However, this potential problem may be
minimal. According to the NA WC seeding logs, the HI available AgI generators for the Boise
project were never all used during a single storm. An average of 8.4 generators were

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