August 16th, 2011

-Assessment of current water conditions

- Precipitation Forecast

- Recommendations for Drought Monitor

Temperature Departure from Normal08/8/2011 – 08/14/2011

VIC Soil Moisture Percentiles14 August 2011

eMODIS VegDRI – 08/07/2011

Cortez Reference ET – SW CO

Center Reference ET - SLV

Avondale Reference ET – AR Basin

NIDISWeeklyClimate,WaterandDroughtAssessmentSummary

UpperColoradoRiverBasinAugust16,2011

PrecipitaEonandSnowpack

Water‐year‐to‐date(WYTD),mostoftheUpperColoradoRiverBasin(UCRB)receivednearoraboveaverageprecipitaEon.TheUpperandLowerGreenRiverbasinshavereceivedover200%oftheiraverageWYTDprecipitaEoninmanyspots.ThesouthernporEonoftheUCRBhasbeendrier,seeingaround70to100%ofaverage.Fig.1showsthataccumulatedprecipitaEonto‐dateforAlamosaintheSanLuisValleyhasbeenmuchbelownormalsinceApril.AttheendofAugust,Alamosanormallyreceivesjustover6inches,butthisWYTD,theyhaveonlyreceivedjustover2inchesandcouldbeseeingtheirdriestwateryearonrecord.

ForthemonthofAugustsofar,precipitaEonhasfavoredColoradoeastoftheUCRB—muchoftheplainsandFrontRangehavereceivedbetween0.5to3.5inchesofraininthelasttwoweeks.Lastweek,thunderstormswerespoYythroughouttheUCRBandeasternplainsofCO(Fig.2).IsolatedareasinsoutheastandnortheastCOreceivedaroundaquarterinchtonearly2inchesofprecipitaEonfortheweek,whilemostoftheFrontRangewasdry.MostoftheUCRBandSanLuisValleyreceivedlessthanaquarterinchfortheweek.

Fig.1:Water‐year‐to‐dateaccumulatedprecipitaEonatAlamosa,CO. Fig.2:August7–13precipitaEonininches.

StreamflowandWaterSupplyAsofAugust14th,about92%oftheUSGSstreamgagesintheUCRBrecordednormal(25th–75thpercenEle)orabovenormal7‐dayaveragestreamflowswith60%ofthegagesrecordingflowsabovethe75thpercenEle(Fig.3).KeygagesontheColoradoRiverneartheCO‐UTstatelineandtheGreenRiveratGreenRiver,UThaveabovenormal7‐dayaveragestreamflowatthe84thand89thpercenEles,respecEvely(Fig.4).StreamflowontheSanJuanRivernearBluff,UTisatthe25thpercenEle.

AferlargestoragevolumeincreasesthroughouttheUCRBforthemonthofJuly,allofthemajorreservoirs’storagevolumesarenowdecreasing,withFlamingGorge,LakeGranby,andLakeDillonseeingonlyminordecreases.AllofthemajorreservoirsaboveLakePowellarecurrentlyabovetheiraverageAugustlevels.ThisApril–Julyperiodwasthe3rdweYestwithregardtoinflowsintoLakePowellsinceoperaEonsatGlenCanyonDambeganin1963.Powell’scurrentlevelisthehighestAugustlevelit’sbeensince2001.

Fig.3:7‐dayaveragedischargecomparedtohistoricaldischargeforAugust14th.

Fig.4:USGS7‐dayaveragedischargeoverEmeattheCO‐UTstateline(top),GreenRiver,UT(middle)andBluff,UT(boYom).

WaterDemandLastweek,thenorthernporEonoftheUCRBexperiencednearaveragetemperatureswhiletheFourCornersareaconEnuedtoseeaboveaveragetemperatures.TheFrontRangeandsoutheastCOwerealsowarmerthanaveragefortheweek.ThewarmertemperatureshavecontributedtohigherreferenceevapotranspiraEon(refET)indroughtstrickenareas.IntheFourCorners,refETiscurrentlyjustaboveaverage,ontrackwiththedrieryears.IntheSanLuisValleyrefETiscurrentlytrackingabovethehighestrefETyear,duringthedroughtof2002—soprecipitaEonfallingtherecouldbequicklylosttotheatmosphereagain.VeryhighrefETratesarealsoseenintheArkansasRiverbasin,thoughimprovementshavebeenseenoverthepastcoupleofweeks(Fig.5).

SoilmoisturecondiEonsremainpoorfortheSanLuisValleyandsoutheastCO.SoilmoistureisaboveaverageformuchofnorthernUTandthenorthernmountainsofCOwhilesoilshavebeguntodryoutinnortheastCO.SatelliteimageryofvegetaEoncondiEonsshowverydryvegetaEonwithliYlegrowthintheSanLuisValleyandsoutheastCO(Fig.6).VegetaEonscondiEonsaremoistforthenorthernporEonoftheUCRB,slightlydryintheFourCornersarea,andarenearaverage,butgejngdrier,fornortheastCO.

PrecipitaEonForecastAweakupperleveldisturbancewillmoveacrosstheUCRBearlyTuesdayandsparkisolatedshowersandthunderstormsoverhigherelevaEons.Moisturewillbeonthedecline,sothethreatofheavyrainwillremainlowthroughouttheday.ThisdryingtrendwillconEnuethroughoutWednesdayandtherestoftheweek.Bythisweekendmonsoonalmoisturewillagaintrytoworknorthward,butitdoesnotappearasthoughitwillmakeitveryfar.ScaYeredthunderstormswillbemostnumerousinthesouthernareasofthebasinaroundtheFourCornersareaandintheSanJuanmountains.ThisacEvitywillbeonthedecreasebyearlynextweekasaPacifictroughsweepsthroughandsupressesmonsoonalmoisturebacktothesouth.

Fig.5:ReferenceevapotranspiraEonsinceApril1statAvondale,COintheArkansasRiverbasin.

Fig.6:August14thVegDRImap,basedonsatellite‐derivedobservaEonsofvegetaEon.

DroughtandWaterDiscussion

NochangesarerecommendedintheUCRBforthecurrentU.S.DroughtMonitor(USDM)map(Fig.7).VeryliYlechangeshavebeenseenaroundtheFourCornersarea,sotheD0/D1thereissElljusEfied.

StatusquoisalsorecommendedforsoutheastCO.ThoughprecipitaEonmapsshowsomeaccumulaEonsaroundfarsoutheastCO,someoftheseobservaEonsseemquesEonableandtheregionsEllremainsverydry.

OneareatowatchinthecomingweeksaheadisnortheastCO—aroundMorgan,Washington,andYumacounEes.SomeslightprecipitaEondeficitsareshowingupintheareawithSPIslessthan‐1onthe60dayandwateryearEmeperiods.VegDRIandtheVICsoilmoistureproductarealsoshowingsomedryvegetaEonandsoilsintheregion.StatusquoisrecommendedatthisEme,butanintroducEonofD0couldbewarrantedinthenearfuture.

DroughtcategoriesandtheirassociatedpercenEles

Fig.7:August9threleaseofU.S.DroughtMonitorfortheUCRB