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<br />1. Introduction <br /> <br />This technical report is an investigation into the feasibility of using artificial ice nucleation, <br />commonly called cloud seeding, in winter clouds over the mountains of Colorado for the purpose <br />of enhancing the seasonal snowpack. Snowpack enhancement results in increased spring and <br />summer stream flows, important for many water resources purposes including irrigation, power <br />generation, recreational, municipal and industrial uses, and improving the environment. Many <br />cloud seeding projects since the 1950s to the present have claimed seasonal snowpack increases <br />which are generally in the 5-15% range. However, these claims are not universally accepted, <br />especially by the scientific community. That is in large part because of the complexities of <br />demonstrating a relatively small snowpack increase when the seasonal snowpack is known to <br />naturally vary by many times the claimed increase. Most of the claims are based on statistical <br />analyses, often using the historical target-control regression method well known to have serious <br />potential flaws (e.g. Dennis 1980). The most recent weather modification policy statement of the <br />American Meteorological Society (AMS 1998) states that, "Whereas a statistical evaluation is <br />required to establish that a significant change resulted from a given seeding activity, it must be <br />accompanied by a physical evaluation (emphasis added) to confirm that the statistically observed <br />change was due to the seeding." Surprisingly few winter cloud seeding experiments or operations <br />have met that test over the years, in part because of the lack oflong-term commitments to <br />research funding. Federal research support has been very limited during the past several years, so <br />progress has been slow. Although there have been some notable successes with winter <br />orographic cloud seeding experiments, the field remains controversial. <br /> <br />The extent of the controversy can be demonstrated by two recent reports. First, the National <br />Research Council published a report in October 2003 (NRC 2003), the conclusions of which was <br />given considerable coverage by the national media. The report concluded that, "--- there is still <br />no convincing scientific proof of the efficacy of intentional weather modification efforts. In some <br />instances there are strong indications of induced changes, but this evidence has not been subject <br />to tests of significance and reproducibility." However, it is also noted that, "There are strong <br />suggestions of positive seeding effects in winter orographic glaciogenic systems (i.e., cloud <br />systems occurring over mountainous terrain." But suggestions fall short of proof in the sense that <br />term is used by scientists and statisticians. <br /> <br />Second, a review panel of the Weather Modification Association (WMA), with significant <br />input from the membership, replied to many of the NRC findings in Boe et al. (2004). The WMA <br />article correctly pointed out that, "--- the NRC panel members collectively had very limited <br />experience or knowledge in weather modification operations, especially in recent years." The <br />two authors of this report consider the NRC panel members to be especially lacking in expertise <br />in recent winter orographic cloud seeding research as well as operations. Boe et al. (ibid.) <br />provided a lengthy rebuttal to many of the NRC findings. This report will not comment further <br />on the NRC and WMA findings, and only cite the respective reports as evidence that weather <br />modification in general, and winter orographic cloud seeding in particular, are still controversial <br />with a wide range of existing viewpoints. <br /> <br />The goal of this report is to address three general topics related to assessment of winter <br />orographic (mountain-induced) cloud seeding feasibility in Colorado. Two topics are <br />fundamental. First is the examination of supercooled liquid water (SL W) cloud over mountains. <br />Unless excess SL W is relatively abundant there can be no realistic hope of seeding potential for <br />snowfall augmentation. It will be shown that SL W availability and amounts do not present a <br />serious limitation to cloud seeding potential in Colorado. <br /> <br />1 <br />