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<br />e <br /> <br />e <br /> <br />snowfall during some phases but very inefficient during other phases (e.g., Super and <br />Holroyd, 1989) <br /> <br />Frequency of snow storms might provide a crude indication of frequency of seedable <br />events. In general, it can be stated that the frequency of storms passages increases from <br />south to north across the Basin. However, the few m~or snowstorms per winter are more <br />common in the southern Basin. Estimated average snowfall per winter was presented by <br />Weisbecker (1972) for the Upper Colorado River Basin. All the m~or mountain barriers <br />across the Basin all were in the range 20-30 inches water equivalent. To the extent <br />seasonal snowfall is related to seedable conditions, the larger, higher barriers would offer <br />more frequent seeding opportunities. However, the range is not great for the barriers <br />above 9000 ft. <br /> <br />The various rating factors are expanded upon in the following: <br /> <br />1. Practical low-level aircraft sampling <br /> <br />Practical low-level aircraft sampling was estimated as either "yes" or "no" depending <br />upon whether an aircraft could realistically be operated at of below 600 m above the <br />average terrain in the higher portions of the target area. It was assumed that in all <br />potential areas, it would be possible to obtain a FAA waiver allowing IFR operations to be <br />conducted to within 300 m above the highest terrain within 5 nm of the flight path. Map <br />inspections were. made to establish the average terrain height near the most probable <br />instrument sites in each target area, and evaluations made concerning the minimum <br />aircraft sampling heights possible given terrain features. Judgements were also made on <br />the potential for terrain-induced turbulence which would preclude safe flight operations. <br />A summary rating form was developed and completed for each potential area. <br /> <br />2. Airspace conflicts <br /> <br />Airspace conflicts were evaluated based on aeronautical chart data coupled with <br />information obtained from FAA Air Route Traffic Control Centers during past programs. <br />Serious airspace conflicts were rare in the areas under consideration, primarily due to <br />their remoteness. Military operating areas potentially restrict operations near the White <br />Mountains of Arizona, as do high traffic areas near the Denver and Aspen areas of <br />Colorado. <br /> <br />3. Winter road access <br /> <br />Winter road access to and around the barrier top refers to existence of an all-weather road <br />to the higher elevations of a potential experimental area. Two areas were rated excellent <br />in Table 2 because highways not only reached the top of the barrier, but crosse'd a m~or <br />portion of its higher elevations. Other ratings ranged from "none" to '''poor" to "fair" to <br />"good". The latter three subjective ratings were primarily based on map evaluation of <br />how well existing all-weather roads provided access to the higher elevation and center <br />portions of each potential experimental area. <br /> <br />8 <br />