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<br />::::> <br />...... <br />t::) <br /> <br />c:..J:~.IATE <br /> <br />. , <br />~ <br /> <br />The climate of the U?per Colo"ado River Basin is due principally <br />to the influence of ~o~~t~in rfiL~ez on the ~ove~e~t of ~ir ~aS3es. The <br />high moc:::-.te.ins are c0:::!?ara~.ively -,.et a:id coel, ....hile th~ plateaas and <br />lo,:er r;o'..ffitains t'.Ye dr:,'0T a~d ~ubj'::ct to .!ici{: ran;:es of tE:,:"erature. <br />Tt:~ intedor valleys :.it the lo....er elevati~!"!s t..re hot a::.d dry in ~ULJ::1er <br />aJ;-' cold in .....inter. <br /> <br />,,1a:;ses of :noist Pacific :'!.ir '..,:.ich approach frDt.! t::e -"rest co~;only <br />nave entirely :.;:r055 the basir.. Dry polar air from the nartl: and moist <br />tropical air fron the south p;:>netrate tLe basin at tir::l':O's. bt:1: r.::.rel:1 <br />all the lIay across. All these types of air rr,aS.3es are obstructed d..'1d <br />ceflectc!J. bj' the encircling mountains so t::at ....ithin th,! basin their <br />effects are wea~er a~l ~ore erratic than i~ ~05t ether ?~rts c~ the <br />Ur.ited St:>.tes. <br /> <br />l.~ost of the I:!Oistu!'e for precipi tatio;J. on the :.lppe!"' t~3i~ is <br />derived fro:n the Pacific Ocean C:.r:d t:;.i') G'.uf of !':exico, .....hose nearest <br />coast~ nre 600 ar;d I,COO !tiles :1..":(", re;;,::;'~ctively. The Paci~ic source <br />predo:ninates fenerally fro~ &~out Octorer th~oUfh April; the Gulf <br />source, during the late =;:,!'ing r'Ild e3.,l~r s~er. <br /> <br />figure 3 shows monthl:" precipitation a:;d ave:-'l,;:"e- !!',onthly tetrtTlera- <br />ture at 11 woather stntic~s in the urper ba~in. Except in the southern <br />part of the basin, the ~onthly precipitati~n is [reater in ~~ntcr. The <br />e.lti tude, as ...ell an the l.'l.ti tau.:" of tl1e cli,natolo.:;ic ..>tation, :1otlce- <br />ebl:." in~l'lences the a'lera~e yef'.rly teL'";:-~ratcre. <br /> <br />~11e eV~ra~e y~arly precipi~tio~ ranges from le~3 than 6 inches on <br />certaiii lo.....land are~s to more t~",-'1 uO i~.;~;(:s in part;:; cf the l.'ind River <br />F~n["e and 5a:! Jusn t.lou:1tains. {,.re:!.l d::.:::.ritu+ic:l of t.!";.is yearlY aver- <br />ace (caIendp.r yp.<::.rz 1921-1950) i~ ;ell':!.,,!:! by Tll'::1le 1; t~is tal-Ie ir.d::.- <br />cates t~at the :Ilean ~'~arly precipi"Cf!.ti('f or, t:.e upper bf.3in is 15.9.' <br />inches. For the \{9.ter years 191}~-I'.)57, a rericd 'J~ich t:,is state:'!lent <br />te.Y.es as 8. sta:1card, the :!e<l.~ :{'2<:or:y ~rec:-ita.ticn is cc'::-,~ut..:"c "to h~ve <br />bC:€n 15.83 inches, f!"ecl?itatior of "th.. h.tter ano'.U,t 0:: the 109,500 <br />s~uare ~ile3 in the cnper basi;: ~culd be ~1uiv~le::t to 92,74Q,000 acre- <br />f",et of -."ater. Averaee ye"l.rl:r evaror.J.tion fro:::; la~"e.s o.:-.J. other open- <br />vlc-ter .3u:-i'ace3 in the u:;r;:er r.psin rar:::~5 nbout frc:J. 28 to ECl inches; <br />tLe yerirl:i vol1.ll!'e is about 575,000 a.c~'e-feet (Table 2). <br /> <br />7 <br /> <br />