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<br />S~R RAI~STORM TYPES &~D ASSOCIATED RAINFALL CHJL~CTERISTICS I~ EASTERN MONT&~A
<br />
<br />Joey Boatmanl" Arlin Super and Edmond Holroyd, 1112
<br />
<br />IMontana Department of Natural Resources and Conservation
<br />Miles City, ~ontana
<br />
<br />2Bureau of Reclamation
<br />Mlles City. Montana
<br />
<br />1.
<br />
<br />INTRODUCTION
<br />
<br />An important consideration in designing
<br />'Taitffa:l~ augmen'ta1:ion exp~rimen't.~is.. 'the na:~lJ~e.of
<br />the storms that produce significant rain in the
<br />r~glon of interest.
<br />
<br />The High Plains Cooperative Program
<br />(HIP LEX) is endeavoring to develop a scientifically
<br />sound and socially acceptable technology for summer
<br />rainfall augmentation at three experimental sites:
<br />Miles City, Montana. Colby-Coodland, Kansas, and
<br />Big Spring-Snyder, Texas. The atmospheric phenomena'
<br />responsible for the nat-ural precipitation at these
<br />sites have both similarities and important differ-
<br />ences. Gabriel (1967), Huff (1969) and Ackerman
<br />et ale (1976) strt!ss the ne~d for measuring natural
<br />precipltution chanlctcristics ::luch as storm types,
<br />frequency of occurrence, duratIon, amount, ar~a.!.
<br />coverage and diurnal timing in any region of
<br />interest for cloud seeding. This wor~ discusses
<br />these meteorological. conditions as observed near
<br />Miles City, Montana, during Hay through July, 1976.
<br />
<br />Ie is also of incerest to invesrigate ho'",
<br />modifying the various storm types might afft:ct the
<br />seasonal rainfall. '!.'oward this t:nc..!, t!\t~ hypo-
<br />clletical seeding moduls of Huff and Chungnon (1972)
<br />wt=re applied to the ~tiles C.lty rai.nfall scat1sc:lc::i
<br />for the 1976 season.
<br />
<br />2.
<br />
<br />DATA SO~RC!~S
<br />
<br />Miles City, Xontana, is located in the
<br />semi-rugged terrain of southeastern Nontana. Its
<br />average annual precipitation is only J30 mm,. but
<br />Miles City .receives about 200 mm of the total
<br />during Hay through July. Fig. i depicts the
<br />Hiles City research area, the C-band.weathe=r radars
<br />at ~11es City and Baker, and the rain gage network
<br />near Terry.
<br />
<br />The rain gage network, centered 55 km
<br />northeast of Miles Clty. consisted 2f 109 sites
<br />in a circular array 2f area 1700 km resulting in
<br />a density of 15.5 km pe r gage. Belfort weighing
<br />rain gages we're used to coll~cc daca throughout
<br />the May through July f!.eld l:H::U::iOn. The rainfall
<br />data were extracted into l5-minute totals for tlte
<br />daily periOd of radar opcrution (1130-0200 MDT),
<br />and into 3 hour totals for the remainder of each
<br />day. These data were cOIIlblnt:.d lnto SCOLtIl. total
<br />
<br />precipitation amounts using the storm definition In
<br />M'Sect:1an 3. Areal "'C'.a'i"ftt-all "escima.te-s- .averngel over.
<br />several hours, typical of many of ,the observed storm
<br />durations, are expected to be within about 5% of I:he
<br />true valoes (Iluff, 1970; Eddy, I9~5, 1976),
<br />
<br />. , "-::1-; :~';,': ;,1
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<br />~ RAOM & RAWlNSONOE SITE
<br />---RAOf,R Of,T,\ COLLECTION AR!:A
<br />~ R,\IN GrlGE NETWORK
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<br />SmUTl ~{m
<br />f,i1LES
<br />
<br />Figure 1
<br />
<br />~lJ.es City. Moncana. rHsearch area and
<br />faclliti<:s.
<br />
<br />GOES satellite imagery "ith 2.km resoln'; "
<br />tion were also available throughout the field season,
<br />They we~~ usee to determine acarml origins and to
<br />assisc in identifying the 9yn.OptJ.~ and. TTtC$O-scale ,
<br />phenomena responsible for the 8CO;rm::l observed. '!'he
<br />imagery was especially useful In ~dentifying and
<br />cracking mountaln-generat~d thunder9torm~.
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