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Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. a I i: U^A United States Department of Idaho Agriculture Natural Resources Conservation Basin Outlook Service March 2001 1, AN'mNNA SNOW DEPTH SENSOR SOLAR PANEL [MPERATURE SEN PRECii Crater Meadows SNOTEL Site, North Fork Clearwater River Basin, Idaho Basin Outlook Reports and Federal - State - Private Snow Cooperative Surveys For more water supply and resource management information, or to subscribe to this publication Contact - - Your local Natural Resources Conservation Service Office or Natural Resources Conservation Service Internet Web Address Snow Surveys http://idsnow.id.nrcs.usda.gov/ 9173 West Barnes Drive, Suite C Boise, Idaho 83709-1574 (208) 378-5740 How forecasts are made j Most ofthe annual streamflow inthe western United States originates as snowfallthathas accumulated in the mountains during the winter and early spring. As the snowpack accumulates, hydrologists estimate the runoffthat will occur when it melts. Measurements ofsnow water equivalentat selectedmanual snow courses and automated SNOTEL sites, along with precipitation, antecedent streamflow, and indices ofthe ElNino / Southern Oscillation are used in computerized statistical and simulationmodels to prepare runoffforecasts. These forecasts are coordinatedbetweenhydrologists intheNatural Resources Conservation Service andtheNationalWeather Service. Unless otherwise specified, all forecasts are for flows < that would occurnaturallywithout anyupstreaminfluences. Forecasts ofanykind, ofcourse, are notperfect. Streamflow forecastuncertainty arises ifromthree primary sources: (1) uncertainknowledge offuture weather conditions, (2) uncertainty inthe forecasting procedure, and (3) errors inthe data. The forecast, therefore, mustbe interpretednotas a single valuebutratheras a range ofvalues with specific probabilities ofoccurrence. The middle ofthe range is expressed bythe 50% exceedance probability forecast, forwhichthere is a 50% chancethatthe actual flow will be above, and a 50% chancethatthe actual flow will be below, this value. To describe the expected range aroundthis 50%value, four other forecasts are provided, two smallervalues (90% and 70% exceedance probabihty) andtwo largervalues (30%, and 10% exceedance probabihty). For example, there is a 90% chance thatthe actual flow will be morethanthe 90% exceedance probabihtyforecast. The others can be interpreted similarly. The widerthe spread amongthese values, the more uncertainthe forecast. As the season progresses, forecasts become more accurate, primarilybecause a greaterportion ofthe future weather conditions become known; this is reflected by a narrowing ofthe range aroundthe 50% exceedance probabihtyforecast. Users shouldtakethis uncertainty into consideration whenmaking operational decisions by selecting forecasts correspondingtothe level ofrisk they are wiUing to assume aboutthe amount ofwaterto be expected. Ifusers anticipate receiving a lesser supply ofwater, or ifthey wishto increase their chances ofhaving an adequate supply ofwater fortheir operations, they may wantto base their decisions on the 90% or 70% exceedance probabihty forecasts, or something in between. Onthe otherhand, ifusers are concerned about receiving too much water (for example, threat offlooding), theymaywantto basetheir decisions on the 30% or 10% exceedance probabihty forecasts, or something inbetween. Regardless ofthe forecast value users choose for operations, they shouldbepreparedto deal with eithermore or less water. (Users should rememberthat even ifthe 90% exceedance probabihty forecast is used, there is stih a 10% chance ofreceiving less thanthis amount.) By using the exceedance probability information, users can easily determine the chances ofreceiving more or less water. The United States DepartmentofAgriculture (USDA) prohibitsdiscrimination inall Itsprogramsandactivitiesonthe basisofrace, color, nationalorigin, gender, religion, age, disability, political beliefs, sexualorientation, ormaritalorfamilialstatus. (Notall prohibited basesapplytoall programs.) Personswith disabilitieswhorequirealternative meansforcommunicationofprogram information (Braille, largeprint, audiotape, etc.) shouldcontact USDA'sTARGET Centerat202-720-2600(voiceandTDD). Tofileacomplaintofdiscrimination,write USDA, Director, OfficeofCivil Rights, Room326-W,Whitten Building, 14th and IndependenceAvenue, SW, Washington, D.C.,20250-9410, orcall (202)720-5964(voiceandTDD). USDAisan equalemploymentopportunityproviderandemployer. IDAHO WATER SUPPLY OUTLOOKREPORT March 2001 1, SUMMARY Idahowaterusers shouldprepareforwellbelownormalrunoffvolumesthis summer. Water supplies willbe marginal atbest. Thekeyishowtousethis limitedandvaluableresource inthebestmanner. Muchless hydropowerwillbeproducedas aresultofnearrecordlow snowlevels inthePacificNorthwest. Electricity buybackoffers are currentlybeingdiscussedbyhydropowercompanies andirrigatorsto save havingtopay higherelectricrates. Conservationwillbethekeythis summerto stretchthemarginal water supplies. With less thenamonthofthe snow seasonleft, hereiswhatweknow: Monthlyprecipitationacrossthe statewaswellbelownormalforthe 2nd consecutive monthat only 35-70%of average. Snowpacks arethe 2ndlowestsince 1961 fromthePayettebasinnorth and inYellowstoneNational Park. Streamflowforecasts decreasedfiromlastFebruaryandnowrangefrom40-70%ofaverage across the state. Reservoirs are notexpectedtofillthisyear, withthe exceptionofAmericanFalls andBrownlee reservoirs, andwillbe drafted earherthannormal as aresultofdismal inflows. Mostwillbe drainedby summer's end. Irrigators inthePayette, Boise, Upper Snake andBearRivermayhavejust an adequate irrigationsupply. Irrigationshortages are expectedinthe central and southcentral Idahobasins. Natural streamflowirrigatorswill seewellbelownormal levels and shouldpreparefor shortages. MotherNature hasthe lasttwo cardstoplayto completethisyear'swater supplypicture - springprecipitation and summerprecipitation. Acoolwetspringwill delaythe snowmeltandinitial irrigation demand. Adiy springand summer, likelastyear, willtaxthe systemevenmore andpossibly setthe stageforanotherbadfire season. In eitherscenario, waterusers shouldbepreparedforextremelylow streamvolumes as well as minimum streamflowlevelsto occurbymidto late summer. SNOWPACK Don'tletthevalleysnowintownfoolyou. There's notmuchsnowinthe mountains. ThePayette, Salmon, ClearwaterandPanhandleRegion snowpacks are 45-55%ofaverage andthe 2ndlowest since at least 1961. Only 1977 hadless snowwaterthanthisyear. SimilarlyinYellowstoneNationalPark, fourcombined long- term snow measuringstations arethe 2ndlowest since 1938; only 1977 hadless snowthanthisyear! In 1977, theMarch 1 snowpackwas only 10-40%ofaverage. Overallthe snowpackinthe SnakeRiverabove Palisades Reservoiris 60%ofaverage, the 3rd lowest since 1961. TheHeniysFork, BigLost, BigWood andBoise snowpacks areabout 57%ofaverage andthe 3rdor4thlowest since 1961. Thebest snowpacks are across southernIdahofromthe OwyheebasintotheBearRiverbasinandrangefrom65-80% ofaverage. Coldtemperaturesthisyearhavekept snow onthe groundinthevalleys longerthenusual. Spokane Airportin Washingtonjust setanewrecord of117 consecutive days withatleast 1 inchofsnowon the ground. Some low to mid-elevation snowmeasuringstations havemore snowwaterthanhigherelevation sites intheBoise and Clearwaterbasins. Inalow snowyearlikethisyear, this isnot a good signbecausethe highelevation snowpackprovidesthatmidto late summer streamflow. PRECIPITATION Februaryprecipitationrangedfromalowofabout40%ofaverageinthe Salmon, west-central, central and southwestcomerofthe stateto 65%inthe Clearwater, Upper Snake andBearriverbasins. Actual amounts were inthe 0.5 - 6.0 inchrange; normalFebruaryamoimts shouldbe inthe 2-9 inchrange. Wateryearto date precipitationrangesfrom47%ofaverageinthePanhandleRegionto 68%acrossthe southernIdahoborder. Withonlyonemonthleftinthe snow season, little hoperemainsto improvethe snowwatercontentlevels to a much higherlevel. Acoolwet spring, April-May-June, woulddelaythe onsetofsnowmelt, initial irrigation demand, andprovide additional soil moisture duringtheplantingseason. RESERVOIRS Reservoir storage remainsfairlysteadyfrommonthto monththisyearas aresultofthe lack ofwinterrains and no draftingforfloodcontrol. The lackofwinterrains has also resultedinbelow normal streamflows whichis notallowingreservoirstorageto increase asittypicallydoes duringthewinter. Reservoirs orreservoir systems that are 53-63%offullinclude: Dworshak, Payette, Boise, Little Wood, andBearLake. The 8 majorUpper Snakereservoirshave acombined storageof69%full, however. Palisades is onlyhalffiill. SalmonFalls Reservoirand Coeurd'AleneLake are only 11%ofcapacity. OakleyReservoiris 34%fiiU; and Owyhee Reservoiris 41%full. BrownleeReservoirremains at 92%ofcapacity, buttheprojectedinflow toHell's Canyon Damis only41%ofaverage. None ofthe majorreservoirs orreservoir systems are expectedto fill thisyear. Draftingwill occurearlieras aresult ofthelack ofstreamflow. Manyreservoirswillbe neartheirminimum levelsby summer's end. Note: NRCS reportsreservoirinformationinterms ofusablevolumes, whichincludesbothactive, inactive and in some cases dead storage. Otheroperatorsmayreportreservoircontents in differentterms. Foradditional information, seethereservoirdefinitions inthis report. STREAMFLOW The lackofFebruarymoistureresultedin streamflowforecasts droppinganother 5-10 percentagepointsfi’om thepreviousmonth. Streamflowforecasts nowrangefrom40-70%acrossthe state. The lowestforecasts callfor 40-50%ofaverageinthePendOreille, Weiser, Payette, Boise, BigWood, Blackfoot, AmericanFalls, andHells Canyondrainages. Thelackofmoisturethiswinterhas also resultedinsomenaturalflowing streams neartheir minimumforthistime ofyear. November-January streamflowvolumes asprovidedbytheUSGS are about25% ofaverageinthe Coeurd'Alene, St. Joe andWeiserrivers, and45%forDworshakReservoirinflow. Elsewhere, November-Januaryvolumeswere 55-75%ofaveragewiththe exceptionoftheBigWood andLittle Wood rivers whichwere nearnormal dueto Octoberprecipitationat250%ofaverage. Irrigation shortages are expectedinthe central and southcentralIdahobasins as indicatedbythe Surface Water SupplyIndex (SWSI) andforuserswho divertdirectlyfromthe stream. Userswill see streamflowlevels returntobaseflow levels earlierthan normal andpotential minimum streamflowlevels occurringinmidto late summer. Irrigators who relyon storagewaterintheBoise, Payette, Upper Snake andBearLakewiU have amarginal supply atbest. Wateruserswhorelyonsmallreservoirs orinstreamwaterwill experience shortages. RECREATION Coldtemperatures acrossthe state arekeepingthe snowpackfirmandprovidingexcellent skiingopportunities atIdaho ski resorts evenwiththelackofsnowfallthisyear. However, backcounty skiers and snowmobilers are findingathin andunconsolidated snowpackwhichis makingtravel difficultand hazardous to equipment. Our Snow Surveysnowcatcouldbarelymakeitthroughthe dryfluffy snowinthe Weiserbasinthe end ofFebruary, norhavewetakenour snowmachines outthisyear. Reports are cominginofsnowmobilersbreakingtheir machines onrocks and stumpsthat arebarelycovered. Be careful outthere! Riverrunners shouldbe makingplanstoputontheriverearlierthisyear. Thehighwater seasonwillbe nearly non-existentas a resultofthe low snow, howeverthiswill alsoprovide alongboating season onthe main SalmonRiverthisyear. Streamswillreturntobaseflowlevels muchearlierthan normal, especially on the tributariesbymid summer. Boaters ontheMiddleFork SalmonRiver should expecttofly into Indian Creek Guard Stationbymid summer, orhave arockyridefromBoundary Creekput-in. Reservoir storage waterwill help extendthe riverrunningseason onthePayetteRiverandprovide more consistent levels. Powerboaters andrecreationists atreservoirswill experience earlierdrawdowns dueto dismal inflows. 1 IDAHOSURFACE WATERSUPPLYINDEX(SWSI) As of March 1, 2001 The Surface Water SupplyIndex(SWSI) is apredictiveindicatorofsurfacewateravailabilitywithin a watershedforthe springand summerwateruse season. Theindexis calculatedbycombiningpre-runoff reservoir storage (carryover)withforecasts ofspringand summer streamflow. SWSIvalues are scaledfrom +4. (abundant supply) to -4.1 (extremelydry), withavalue ofzero indicatingamedianwater supply as comparedto historical occurrences. SWSIvalues arepublishedJanuarythroughMayandprovidea more comprehensive outlook ofwater availabilitythaneither streamflowforecasts orreservoir storagefigures alone. The SWSIindex allows comparisonofwateravailabilitybetweenbasinsfordroughtorflood severityanalysis. Threshold SWSIvalues havebeenestablishedformostbasinsto indicatethepotentialforagriculturalwater shortages. Thefollowingagencies and cooperatorsprovide assistance inthepreparationofthe Surface Water SupplyIndex forIdaho: US National Weather Service US Army Corps ofEngineers US Bureau ofReclamation IdahoDept, ofWaterResources Idaho WaterUsers Association PacifiCorp Agricultural Water MostRecent Year With SupplyShortageMay SWSI SimilarSWSI Value Occur When SWSIis BASINorREGION Value Less Than PANHANDLE NA -3.3 1987/94 CLEARWATER NA -2.9 1987/92 SALMON NA -3.1 1988 WEISER -3.3 1994/88 NA PAYETTE -2.9 1991/88 NA BOISE -3.2 1987/91 -2.6 BIGWOOD -2.8 1990 -1.4 LITTLE WOOD -2.2 1990 -2.1 BIGLOST -2.4 1990/91 -0.8 LITTLELOST -2.5 1977 0.0 HENRYSFORK -2.3 1987/90 -3.3 SNAKE (AMERICANFALLS) -2.5 1987/94 -2.0 OAKLEY -1.0 1987 0.0 SALMONFALLS -2.0 1994 0.0 BRUNEAU NA -1.9 1991 OWYHEE NA -1.1 1994 BEARRIVER -1.6 1978 -3.8 -4-3-2-101234 SWSISCALE, PERCENTCHANCEOFEXCEEDANCE, ANDINTERPRETATION I I I I I I I I I 99% 87% 75% 63% 50% 37% 25% 13% 1% Much Below Near Normal Above Much IBelow I Normal | Water Supply | Normal | Above I I I | | | | Note; ThePercent Chance ofExceedanceis anindicatorofhow oftenarange ofSWSIvalues mightbe expectedto occur. Each SWSIunitrepresents about 12%ofthe historical occurrences. As anexample ofinterpretingthe above scale, the SWSIcanbe expectedtobe greaterthan -3.0, 87%ofthetime andlessthan -3.0, 13%ofthetime. Halfthe time, the SWSIwillbebelowandhalfthetime above avalue ofzero. The intervalbetween -1.5 and +1.5 described as "NearNormalWater Supply," representsthree SWSIunits andwouldbe expectedto occurabout one-third (36%) ofthe time. Park Divide National Thumb & Yellowstone River Snake 1938-2001, Lake, Year Lewis Index Snow 1 Camp, Base March j9)eM Mous - soqoui PANHANDLE REGION MARCH 2001 1, Mountain Snowpack (inches) Mountain Precipitation PANHANDLE REGION PANHANDLE REGION Monthly ElYear-to-date 60 50 0) CO 40 o>> < •g 30 <D E 20 0) Q. 10 Oct Nov Dec Jan Feb Mar Apr May WATER SUPPLY OUTLOOK February precipitationwas once again below normal at 57% ofaverage. Monthly precipitation has beenwell below for the past 10 months with the exception ofSeptember 2000. Precipitation, since October 1, is the lowest in the state at a dismal 47% ofaverage. Low elevation snowpacks, such as HaydenLake, are better at 76% ofaverage while the higher elevation snowpacks which provide the bulk ofthe snowmelt runoffare in the 35-45% ofaverage for individual snow measuring sites. Overall, the Panhandle Region snowpack is 47% ofaverage. This is the second lowest since 1969, only 1977 had less snowwater. OnMarch 1977, the snowpack was a meager 38% ofaverage. 1, Coeur d'Alene Lake is only 11% ofits normal summer level, basically at its natural level. Pend Oreille and Priest lakes are about 45% oftheir summer level. Currently, natural streamflow levels are near record low as a result ofthe unusually drywinter. Streamflow forecasts decreased from last month and now range fi'om 50-60% ofaverage. Water users should prepare for much below normal streamflow levels for the rest ofthe water year and earlier return to low flow conditions this summer. - PANHANDLE REGION Streamflow Forecasts - March 1, 2001 «==-— Drier — Future Conditions ——=— Wetter - » 1 Forecast Point Forecast Period 90% 70% 50% (Most Probable) 30% 10% 30-Yr Avg. (1000AF) (1000AF) (1000AF) (%AVG.) (1000AF) (1000AF) 1 (1000AF) 1 KOOTENAI at Leonia (1,2) APR-JUL 2709 3439 3770 52 4101 4831 7199 APR-SEP 3200 3977 4330 52 4683 5460 8275 MOVIE RIVER at Eastport APR-JUL 168 199 220 53 241 272 415 APR-SEP 176 209 231 54 253 286 430 SMITH CREEK APR-JUL 48 62 72 60 82 96 120 APR-SEP 49 65 76 60 87 103 126 BOUNDARY CREEK APR-JUL 46 60 70 59 80 94 119 APR-SEP 48 63 73 58 83 98 125 CLARK FK at Whitehorse Rpds (1,2) APR-JUL 3405 5375 6270 54 7165 9135 11730 APR-SEP 3747 5915 6900 53 7885 10053 12910 PEND OREILLE Lake Inflow (2) APR-JUL 4246 5660 6620 50 7580 8994 13150 APR-SEP 3935 5903 7240 50 8577 10545 14370 PRIEST near Priest River (1,2) APR-JUL 276 372 415 51 458 554 812 APR-SEP 276 382 430 50 478 584 865 COEUR D'ALENE at Enaville APR-JUL 280 383 454 59 525 628 769 APR-SEP 290 397 470 58 543 650 809 ST. JOE at Calder APR-JUL 458 582 666 57 750 874 1169 APR-SEP 485 613 700 57 787 915 1237 SPOKANE near Post Falls (2) APR-JUL 1014 1348 1575 60 1802 2136 2627 APR-SEP 1000 1345 1580 58 1815 2160 2720 SPOKANE at Long Lake (2) APR-JUL 1095 1482 1745 60 2008 2395 2905 APR-SEP 1188 1597 1875 60 2153 2562 3128 PANHANDLE REGION PANHANDLE REGION | Reservoir Storage (1000 AF) - End of February Watershed Snowpack Analysis - March 1, 2001 j Usable *** Usable Storage *** Number This Year as % of Reservoir Capacity This Last Watershed of Year Year Avg Data Sites Last Yr Average HUNGRY HORSE 3451.0 2168.0 2428.0 2205.0 Kootenai ab Bonners Ferry 32 56 49 FLATHEAD LAKE 1791.0 844.0 712.0 881.0 Moyie River 12 59 51 NCXON RAPIDS 335.0 305.9 326.1 298.1 Priest River 4 48 48 PEND OREILLE 1561.3 734.4 711.5 798.0 Pend Oreille River 97 64 59 COEUR D'ALENE 238.5 26.3 124.5 149.1 Rathdrum Creek 5 62 81 PRIEST LAKE 119.3 53.0 50.0 54.6 Hayden Lake 2 64 76 Coeur d'Alene River 8 59 62 St. Joe River 3 51 47 Spokane River 17 59 65 1 1 Palouse River 2 69 79 1111 II * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual flow will exceed the volunes in the table. The average is confuted for the 1961-1990 base period. (1) - The values listed uxler the 10% and 90% Chance of Exceeding are actually 5% and 95% exceedance levels. (2) - The value is natural flow - actual flow may be affected by upstream water management.