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Last modified
7/28/2009 2:28:42 PM
Creation date
10/1/2006 2:16:21 PM
Metadata
Fields
Template:
Weather Modification
Applicant
North American Weather Consultants
Sponsor Name
Upper Colorado River Commission
Project Name
The Potential Use of Winter Cloud Seeding Programs to Augment the Flow of the Colorado River
Title
The Potential Use of Winter Cloud Seeding Programs to Augment the Flow of the Colorado River
Prepared For
Upper Colorado River Commission
Prepared By
Don Griffith, NAWC
Date
3/1/2006
Weather Modification - Doc Type
Report
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<br />Orographic clouds in the mountainous western states are often associated with passing <br />storm systems. Wind flow over a mountain barrier causes the orographic lift to either produce <br />the cloud or enhance cloud developmcnt associatcd with a migratory feature sllch as a cold <br />frontal system. In silu and remote observations of SL W in orographic clouds (Reynolds. 1988) <br />have indicated significant periods of the occurrence of SL W with passing winter storms. These <br />studies have indicated that the preferred location for the formation of zones of SL W is over the <br />windward slopes of the mountain barriers at relatively low elevations (typically reaching only the <br />approximate height of the mountain barrier). Super. 1990. reporting on measurements ofSL \\' <br />observed in \vintcr research programs in the \'.:estern U.S. states that. "There is remarkable <br />similarity among rcsearch results from the various mountain ranges. In general. SLW is available <br />during at least portions of many storms. It is usually concentrated in the lower layers and <br />especially in shallow clouds with wann tops." Another quote from Super (1990) says: "The <br />tcndency for greatest SLW content near the wind\\:ard slopes ofa barrier is clearly shown by <br />Hobbs (1975) from a composite of22 aircraft missions over the Cascade Mountains. and by Hill <br />(1986) based upon 57 vibrating wire sondes over the Wasatch Mountains of Utah. 110lroyd and <br />Super (1984) examined data from many aircralt passes over the flat-topped Grand ~tcsa of <br />Colorado and showed that SL W was concentrated over the windv.'ard slope and barrier top. with <br />higher water contents nearer the surface." <br /> <br />The basic consideration in the development of the design ofa \\inter orographic cloud <br />seeding project is to develop a seeding methodology that will tap this reservoir of SL W to <br />convert water droplets into snowflakes that otherwise would be lost through evaporation ovcr the <br />downwind side of the barrier. In other words. \"..e wish to improve the efficiency of the natural <br />storm system in producing precipitation that reaches the ground. <br /> <br />"If SL W clouds upwind of and over mountain barriers are routinely seeded to produce <br />appropriate concentrations of seeding ice crystals. exceeding 10 to 20 pcr liter of cloudy air. <br />snowfall increases can be anticipated in the presencc or absence of natural snowfall. It has been <br />repcatedly demonstrated with physical observations that sulTiciently high concentrations of seeding <br />agent. effective at prevailing SLW cloud temperatures. will produce snowfall \vhen natural <br />snowfall rates are negligible. Seeded snowfall rates arc usually light. on the order of I mm/hr or <br />less. consistent with median natural snowfall rates in the intermountain West (Super and Holroyd. <br />1997):. <br /> <br />Figure 1 provides a schematic of how cloud seeding using ground generators on a <br />mountainous winter time program is thought to \\'ork. <br />
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