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Last modified
7/28/2009 2:29:05 PM
Creation date
2/27/2007 9:01:05 AM
Metadata
Fields
Template:
Weather Modification
Applicant
Arlin B. Super and James A. Heimbach Jr.
Sponsor Name
Colorado Water Conservation Board and US Bureau of Reclamation
Project Name
Literature Review/Scientific Study
Title
Feasibility of Snowpack Enhancement from Colorado Winter Mountain Clouds: Emphasis on Supercooled Liquid Water and Seeding with Silver Iodide and Propane
Prepared For
Coloado Water Conservatoin Board
Prepared By
USBR
Date
9/30/2005
State
CO
Weather Modification - Doc Type
Scientific Study
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<br />Hindman et at. (1994) cited a typical cloud base value for the windward slope of the Park Range <br />as 9200 ft. Since detailed statistics on Park Range cloud base altitudes have apparently not been <br />published, the lead author spoke with the two scientists believed to be most experienced with Park <br />Range surface observations at the Stonn Peak Laboratory (SPL). One estimated that cloud bases <br />were usually in the range 9100 to 9700 ft (Ed "Ward" Hindman, personal communication, July <br />1999). The other, who currently directs the SPL, believes that cloud base descends as low as 8300 <br />to 8500 ft infrequently, but often enough to be considered (Randy Borys, personal communication, <br />July 1999). However, he estimated that "typical" cloud bases were between 9000 and 9500 ft. He <br />also noted that cloud base is above crest line only 10 percent of the time when snow is falling at the <br />SPL. Borys also stated that cloud bases were rarely warmer than OOC from December 1 through <br />April!. In that case, propane seeding would almost always produce ice crystals as long as the <br />dispenser was in-cloud or not far below cloud base. <br /> <br />Based on the infonnation presented, it appears reasonable to assume most seedable winter <br />orographic cloud bases over the Park Range will be in the range 8500 to 10,500 ft. In order to <br />locate propane dispensers to usually be within SL W cloud, or at least at ice saturation, they should <br />be sited no lower than about 9000 ft which would provide about 1400 ft of vertical lift before <br />passing the mountain crest. Cloud base infonnation for other Colorado mountain ranges is not as <br />readily available as at the Park Range where considerable research has been conducted over <br />decades. But this infonnationjust stated can be used as a guide for other locations. Local ski area <br />personnel could be contacted for cloud base infonnation at their particular locations, but <br />accomplishing that is beyond the scope of this study. <br /> <br />As a matter of interest concerning ice saturation, the levels of ice and water saturation are <br />identical at OOC. For the altitudes and pressures relevant to this study, it has been calculated that the <br />ice saturation level would be about 240 ft below the water saturation level (liquid cloud base) at- <br />50C, and about 460 ft below it at -I ooe. Consequently, propane dispensers will often be ineffective <br />if sited more than a few hundred feet below liquid cloud base. Since visual cloud base may be <br />related to both liquid droplets and falling ice crystals and snowflakes, it will sometimes be <br />significantly lower than liquid cloud base. <br /> <br />5. Characteristics of Supercooled Liquid Water Cloud <br /> <br />This section reviews published infonnation concerning the availability and variability of SL W <br />cloud over mountain barriers, elaborating on the infonnation of Sec. 2. While the primary area of <br />interest is Colorado, the available data set was significantly enhanced by inclusion of Utah <br />measurements. Numerous observations have been made in both states. Utah orographic clouds <br />are believed similar to those in Colorado as the mountains are at similar latitudes in the adjoining <br />states. Cloud observations from further-removed states like Arizona and California are unlikely <br />to be very representative of Colorado conditions, and are generally ignored herein. <br /> <br />In order for winter orographic cloud seeding to succeed, SL W cloud droplets must exist in <br />excess of those naturally converted to snowfall. Tiny cloud droplets can, and often do, exist at <br />temperatures below OOC, the freezing point of bulk water. While natural ice crystals typically <br />form in abundance when SL W cloud temperatures are lower than about -15 to - 20oC, cloud <br />seeding can initiate the precipitation process at wanner temperatures, even slightly below OOC for <br />some types of seeding. It will be shown that primary SL W zones in orographic clouds in <br />Colorado and Utah usually have temperatures wanner than -150C, and often wanner than -1 ooe. <br />Thus, cloud seeding presents an opportunity to enhance snowfall from warmer SL W clouds when <br /> <br />11 <br />
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