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<br />Warburton ct aI. (1995a) reported on short-tcrm (15-30 min) silver-in-snO\\ observations for two <br />central Sierra Nevada projects. Their observed concentrations ranged from 2~()() ppt. most being <br />less than 100 ppt. Since these were short-term \-alul.'S. they cannot ~ directly extrapola((.-d into <br />seasonal concentrations. .\1on.'Over. thl.'SC two operational projects had in1n:qucm proper targeting. <br />l.'Stimall.-d to be only 10-20 pt..'TCenl of ~ tim:. so any SC3.-"0nal valucs would nOI rcpn.'SCnt wcll- <br />=000 larget areas. <br /> <br />Warburton et al. (I QQ5a) also preSt.'OIed calculations of silver concentrations v.hich. might <br />be eXpt..'Clt.-d in the two watersheds by assuming ~ach Agl generator producl.-d 20 icc partic.:les per <br />liter. effective at _lOoe. Concentrations less than 10 per liter have bt.--cn sho.....n to result in <br />negligible snov.faIl ratcs. Further a...suming each icc particle had a 100 micron radius with an AgI <br />particle attacht-d \\ith mass in the rangc shown b~ Warburton el. aL (1995b). calculated silver <br />concentrations in the seeded snov.melt were between 80-ICXJO ppt. However. 100\er values would <br />be cxpt..'Cted because of additional accrck-d water capture by .seeded crystals. and by dilution <br />because of natura] snowHakes. Therefore. the 80-1000 ppt range can be considered the highest <br />....alues expt.."Cted bringing the calculations in Iinc with the obscrvations discussl.>d in this St.'Clion. <br /> <br />Silvcr-in-snow analyses were u.<;t.-d to e\aluate targeting elTl."Ctivcncss of the Upper San <br />Joaquin Waten;hed in the- Sierra Nevada as discussed in an internal report by Stone (1997). Vertical <br />profiles of the 1993/94 seasonal snowpack \\ere- sampled at 2 cm depth I\.'SOlution at six primary <br />target locations. The- per~location fn."queoc)' of ab<)\-c background silver Icvels ranged from 39-100 <br />percent" and averaged 59 percent. indicating good to excelle-nt targcting. St."t.-ding silver <br />concentrations in the 632 samples. each 2 cm thick. ranged from 13 to 121 ppt in the primary target. <br />Seither the me-m nor the mt-dian was reportoo. Both the frequency of seeding silve-r and its <br />concentrations were slated to be higher than those pre..-ious1y measured by DRI in other Sierra <br />:\"cvada seeding programs. Il should be noted that ground-~d S(,.'\..>ding was supplemented by <br />aircraft seeding v.hich may explain somc of the improved targeting v.ith this project. Targeting <br />succes.... was likely also enhanced by having snow-sampling sites located at canyon heads oriented <br />along lhe pn.-dominant v.ind How patt(.~ during SI..'\..-dable slonns. Canyons would be expected to <br />funnel the Agl over mountain barrien;. Tht'refore. the snow sampl~ were eollccted at admittt.-dly <br />"preferred sites." unlikely to be typica} o I' the overall target area.. <br /> <br />Warburton et aI. (l995b) reported on results from a seeding e-xperiment on 20 IA.'Cember <br />1984 in the Lake Almanor projt:et area which employed 10 high altitude ground-based Agl <br />generators. Silver concentrations were sho\\n for 2 cm snow depth samples from a station near the <br />target area cente-r. which appeared to be well targeled. Several samples had gn:ater than 10 ppt. a <br />number had betwt.~n 2~O ppt and the ma.ximum wa.... 8... ppt. The nearest generators We're 12-15 <br />miles upv.ind. <br /> <br />Chai ct al. (1993) presented results from a 5eries of l.ake Almanor storms. which had 2-cm <br />snow depth samples \\ith detinite evidcnce of both seeding silver and a co-released traCt..~ aerosol. <br />That is. these snow samples were certain!>' targeted by the AgI. Silver concentrations from the' 19 <br />samples ranged. from 5 to 207 ppt v.ith a median of 33 ppt. Five of the samples exceeded 100 ppt <br />but only onc \\as greater than 117 ppt. Five samples W\."re in the 5-15 ppt rdJ'1gc. About halfthc <br />samples were betv.-een 20-100 ppt. <br /> <br />u <br />