NIDISWeeklyClimate,WaterandDroughtAssessmentSummary

UpperColoradoRiverBasinJuly6,2011

PrecipitaFonandSnowpack

ForthemonthofJune,muchofthenorthernporFonsoftheUpperColoradoRiverBasin(UCRB)receivedbetween100%to200%oftheiraverageprecipitaFon(Fig.1).TheFourCornerswasthedriestregionofthebasinforthemonth,receivinglessthan30%ofaverage.TheSanLuisValleywasalsoverydryforthemonth,onlyseeingabout10%ofitsaverageprecipitaFon.MuchofeasternColoradoreceivedbetween50%and100%ofaverageprecipitaFonforthemonth,withpartsofsoutheasternCOseeingover100%ofaveragefromjustacoupleofstorms.

Lastweek,theheaviestamountsofprecipitaFonfellovernortheastUtahandsouthwestWyomingwithamountstotallingbetweenhalfaninchtoover2inchesinsomespots(Fig.2).ThemountainsofnorthernCOandnortheastCOreceivedbetweenaquarterinchtoaninchofmoisturefortheweek.ThedroughtstrickenareasinthesouthernporFonoftheUCRBandinsouthernCOremaineddry,seeinglessthanatenthofaninchovertheweek.

Fig.1:JuneprecipitaFonasapercentofaverage. Fig.2:June26–July2precipitaFonininches.

Fig.3:SNOTELWYTDprecipitaFonpercenFles(50%ismedian,21‐30%isDroughtMonitor’sD0category).

ThemajorityoftheSNOTELsitesintheUCRBareshowingveryhigh(andinmanycases,recordhigh)percenFlerankingsforwater‐year‐to‐date(WYTD)precipitaFon(Fig.3).TheRioGrandeandSanJuanbasinsinsouthernCOarethedriest,thoughthehigherelevaFonsoftheSanJuanbasinhaveimprovedsomewhatfromtheearlierpartofthewateryear.SeveralsitesintheSangredeCristosshowpercenFlesworthyofD1–D2.

A_eranearrecordseasonhighforsnowpackintheUCRB,themajorityoftheSNOTELsiteshavenowcompletelymeltedtheiraccumulatedsnowpackfortheseason(Fig.4–whitesquaresindicatesitesthathavecompletelymeltedout).OnlyafewhigherelevaFonsiteshaveremainingsnowpackle_onthem–theTowersiteintheYampaRiverbasinsFllhasover30inchesofsnowwaterequivalent.

Fig.4:SNOTELWYTDaccumulatedsnowwaterequivalentasapercentofaverage.

StreamflowAsofJuly4th,about95%oftheUSGSstreamgagesintheUCRBrecordednormal(25th–75thpercenFle)orabovenormal7‐dayaveragestreamflowswithover70%ofthegagesrecordingflowsabovethe75thpercenFle(Fig.5).AsofJuly5th,1gagewassFllexceedingtheNaFonalWeatherServicefloodstage—theGreenRiveratGreenRiver,UTsite.ManyofthegagesinthenorthernpartoftheUCRBaresFllrecordingreal‐Fmeflowsatorabovethe99thpercenFle,whileflowsinthesouthernpartofthebasinhavereceded.

KeygagesontheColoradoRiverneartheCO‐UTstatelineandtheGreenRiveratGreenRiver,UThaveabovenormal7‐dayaveragestreamflowatthe93rdand96thpercenFles,respecFvely(Fig.6).StreamflowontheSanJuanRivernearBluff,UTisatthe47thpercenFle.FlowsontheSanJuanhaddecreasedasaresponsetothedecreasedreleasesfromNavajocombinedwiththelowersnowpacknowbeingcompletelymeltedout.

Fig.5:7‐dayaveragedischargecomparedtohistoricaldischargeforJuly4th.

Fig.6:USGS7‐dayaveragedischargeoverFmeattheCO‐UTstateline(top),GreenRiver,UT(middle)andBluff,UT(bohom).

WaterSupplyandDemandLastweek,aboveaveragetemperatureswereseenacrossmostoftheUCRBandeasternplainsofCO.Muchwarmertemperatures(6°to8°aboveaverage)wereobservedovertheFourCornersandsoutheasternCO.SoilmoisturecondiFonsremainpoorfortheSanLuisValley.SoilmoistureisaboveaveragealongtheWasatchrangeinUT,inthenorthernCOmountains,andinnortheastCO(Fig.7).SoilmoisturemodelsindicateimprovedcondiFonsoversoutheastCOasaresponsetotheonestormtwoweeksago—thesemodelsarelikelyerroneouslyoveresFmaFngmoisturethatisnotactuallybeingobservedintheregion.

AllofthemajorreservoirsintheUCRBhaveexperiencedrapidstorageincreasesinJune.DailyinflowsintoFlamingGorge,BlueMesa,andLakePowellareallwellabovetheiraveragesforthisFmeofyear.InflowsintoNavajohavedippedbelowtheiraverageforthisFmeofyear.LakePowellhasseenlargeincreasesinvolumeandisnowat83%ofaverage.ItisprojectedthatLakePowell’selevaFonwillconFnuetorisethroughlateJuly—projectedelevaFonlevelswouldbethehighestthey’vebeensinceOctober2001.

PrecipitaFonForecastSincethe3rdofJuly,apahernshi_hasresultedintheinfluxofsubtropicalmoistureintotheUCRBandsurroundingareas.ThisweherpahernwillconFnuethroughThursday,bringingscaheredshowersandthunderstormsthroughouttheregionwithwidespreadtotalsbetweenatenthandaquarterofaninch.Locallyheavieramountsandpossibleflashfloodinginafewspotscanbeexpected.AsanupperlowmovesintothePacificNorthwestonFriday,thesubtropicalmoistureplumeintheUCRBwillshi_tothesouthandeast.BySunday,thewesternedgeofthesubtropicalmoisturewillextendfromneartheFourCornersupthroughsouth‐centralWY.Areaswestofthislinewillseeasignificantdryingtrend,withonlyafewlate‐daythunderstormspossible.AnothertroughwillmoveintothePacificNorthwestearlynextweekandwillbringdriersouthwesterlyflowintotheUCRB.SignificantmoisturewillsFllbepersistentforfareasternCO.

Fig.7:NLDAStotalcolumnsoilmoisturepercenFlesforJune30th.

Fig.8:June27thVegDRImap,basedonsatellite‐derivedobservaFonsofvegetaFon.

DroughtandWaterDiscussion

IntheUCRB,thecurrentU.S.DroughtMonitor(USDM)authorexpandedtheD0intheFourCornersregion,coveringmoreofSanJuanCounty,UTtobehermatchthecurrentVegDRIcondiFonswhichshowdroughtcondiFonsthroughoutthesouthernporFonofthebasin(Fig.8).

StatusquoisrecommendedfortheremainderoftheUCRBforthecurrentUSDMmap(Fig.9).

AD4introducFonisbeingrecommendedforAlamosaCountyintheSanLuisValley.SPIsareverynegaFveonmanyFmescalesandlocalexpertsindicatethatD4wouldbejusFfiedbasedonimpacts.IntheArkansasbasin,anadjustmentofthegradientinCheyenneCountyisrecommended,movingtheD0andD1linestothenorthtobeherdepictthedrynessobservedthere.

DroughtcategoriesandtheirassociatedpercenFles

Fig.9:June28threleaseofU.S.DroughtMonitorfortheUCRB