Laserfiche WebLink
<br />~ <br />t'- <br />c <br />C"". <br /> <br />Bydrometeor01ogieal Conditions <br />Leading to Uke Powell Inflow Forecasts <br /> <br />,~'',.i~ <br />~'& <br /> <br />David A. Westnedge <br />Deputy Hydrologist 1n Charge <br />NIlS, ec.1ol:'ado ~.in liver l!oreCllst CenUr <br />Salt Lake .city, Utah <br />June 14, 1983 <br /> <br />It appe.e.'t'8 that the April-Jl,lly inflow to Lake Powell v1111>e cloae to 14.6 <br />million Aere-fN1:, 210% of normal aDd the higbest :inflow smee 1920. <br /> <br />Streamfl,", forecasts increased rapidly, durins: the nut thne weeks of .tune <br />when observed bflow and t:l,lrren1: conditions of weather and SDovpaclt :U1dicated <br />that a revision of tbe forecasts w.. nece..ary. <br /> <br />to review the sit....U.on it Is best to look at"'the eondit1<>D8 (seasonal pre- <br />c:f.p1tatlou ud snowpack) ad the foreUllt8 beginniDS as of JanU4ry 1. The drain- <br />age ar.... above Lake PC'Nell consl.tIl prilllarUy of three tributaries: the GneD <br />River, the Sara JU811 lU"irer. - ad tbe Colorado River u.i:PsteD,. v.1tb the three' 1"l-..r. <br />c:ontl:'lbut1ng to the vollllll! 1D .. ratio of 2:1:2 respectively. Snovp.ack ud basm <br />averages are .pplied to each :lDdiv1d....lly. <br /> <br />OIl J.n....ry 1 tbe infloW foreean to Lake Powell _s 7.8 lIIf.1l1on acre-feet, <br />112% of. average (6.952 1I11l:l.on A.P.). 'lbe snovpaek in the I,lpper Colorado River <br />vall 120% of nomal. Greea - 142% and tbe San Jwm basin 127%. Basin-vide precip- <br />ltation, October through December, was .enerally near normal but rll4ged frOll 65% <br />to 135%. I'D eady Jazwary mereased releases were started frOlll Hoover baaed on <br />tbe higher than nomal fotee&lltls. <br /> <br />On February 1 tbe forecast decrealled to 7.1 million acre-feet, 102% of aver- <br />age. J8mlBl')' prec:lpUa1:ion vas leas thaD 50% 1D the beadwaters, but aome areas <br />of eastern Utah had 150% of nomal. The DOUIltam BDowpack decl'used _rkedly <br />dUr1ng a UlIl.Ially heavy deposition period; upper Coloz:ado - 89%. upper Green _ <br />81%. and the Sail Juan 120%. Witb tbe drop in the flow forecast, releases trOll <br />Hoover vere auspended... , <br /> <br />On l'larcb 1 the forecast continued to decline to 6." 1I1l11on acre-feet, 96% <br />of average. Fe1>rua'ty preeipj,tation "as generally near normal but r...g.d fr_ <br />80% in the upper Gr_1I River basin to 150% in the lower basins ill the ViCin1ty <br />of Lake Povell. The total Bnowpack chaneed only slightly: upper Colorado River <br />88%, the I,lpper Green River !lasin 80%, and tbe San Juan drainage . 114%. <br /> <br />On April 1 the forecast increased to 7.9 llI1lU.on A. F.. 114% of nOrllial, rs- <br />flec1:ing a vet Harch weatber regime. !'larch precipitation was generally 140 to <br />200% of averaee vith seasonal precipitation near lIermal in the beadvater areas <br />to nearly 200% 1D lower reaches. The 8IO.mtam snowpack improved to 114% of <br />Iovel'age :Ln tbe upper Colorado basin, the Green River 83%,...d the San Juan <br />121% of normal; <br /> <br />APPENDIX B <br />