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Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. ^ £ TD-J-J.Y ANRCS Idaho Water Supply UnitedStatesDepartmentofAjiculture ^ NaturalResourcesConservation Service ^ ^ |j"^ | February 2003 1 o , Magic Reservoir in the Big Wood basin, January 2003 10% of capacity, 22% of average Basin Outlook Reports and Federal - State - Private Snow Cooperative Surveys Formore watersupply and resource management information, orto subscribe to this publication Contact - - Your local Natural Resources Conservation Service Office or Natural Resources Conservation Service Internet Web Address Snow Surveys http://www.id.nrcs.usda.gov/snow 9173 West Barnes Drive, Suite C Boise, Idaho 83709-1574 (208) 378-5740 Water supply forecasts are produced in cooperation and coordination with the National Weather Service, NOAA How forecasts are made Most ofthe annual streamflow in the western United States originates as snowfall that has accumulated inthe mountains during the winterand early spring. As the snowpack accumulates, hydrologists estimatethe runoffthatwill occurwhen it melts. Measurements ofsnowwater equivalent at selected manual snow courses and automated SNOTEL sites, along with precipitation, antecedent streamflow, and indices ofthe El Nino / Southern Oscillation are used in computerized statistical and simulation models to prepare runoffforecasts. These forecasts are coordinated between hydrologists in theNatural Resources Conservation Service andtheNational Weather Service. Unless otherwise specified, all forecasts are forflows that would occurnaturally withoutany upstream influences. Forecasts ofanykind, ofcourse, arenotperfect. Streamflow forecastuncertainty arises fromthreeprimary sources: (1) uncertain knowledge offuture weatherconditions, (2) uncertainty in the forecasting procedure, and (3) errors inthe data. The forecast, therefore, must be interpretednot as a single value but rather as a range ofvalues with specific probabilities ofoccurrence. The middle ofthe range is expressed by the 50% exceedance probability forecast, forwhichthere is a 50% chance that the actual flow will be above, and a 50% chancethatthe actual flow will be below, this value. To describethe expected range aroundthis 50%value, four other forecasts are provided, two smallervalues (90% and 70%exceedance probability) andtwo larger values (30%, and 10% exceedance probability). Forexample, there is a 90% chancethatthe actual flowwill be morethanthe 90% exceedance probability forecast. The others can be interpreted similarly. The widerthe spread among these values, the more uncertainthe forecast. As the seasonprogresses, forecasts become more accurate, primarily because agreaterportion ofthe future weather conditions becomeknown; this is reflected by a narrowing ofthe range around the 50%exceedance probability forecast. Users shouldtakethis uncertainty into consideration when making operational decisions by selecting forecasts correspondingtothe level ofriskthey arewilling to assume aboutthe amount ofwaterto be expected. Ifusers anticipate receiving a lesser supply ofwater, oriftheywishto increasetheir chances ofhaving an adequate supply ofwater fortheiroperations, they maywantto basetheir decisions on the 90% or 70%exceedance probability forecasts, or something in between. Onthe otherhand, ifusers are concerned about receivingtoo much water (for example, threat offlooding), they maywantto basetheirdecisions on the 30%or 10% exceedance probability forecasts, or something inbetween. Regardless ofthe forecastvalue users choose foroperations, they should be preparedto deal with eithermore or less water. (Users should rememberthat even ifthe 90% exceedance probability forecast is used, there is still a 10%chance ofreceiving less thanthis amount.) Byusingthe exceedance probability information, users can easily determinethe chances ofreceivingmore orless water. The United StatesDepartmentofAgriculture(USDA)prohibitsdiscriminationinallitsprogramsandactivitiesonthebasisofrace,color,nationalorigin, gender, religion, age,disability, politicalbeliefs, sexualorientation,ormaritalorfamilialstatus. (Notallprohibitedbasesapplytoallprograms.) Personswith disabilitieswhorequirealternativemeansforcommunicationofprograminformation(Braille, largeprint,audiotape,etc.)shouldcontactUSDA'sTARGET Centerat202-720-2600(voiceandTDD). Tofileacomplaintofdiscrimination,writeUSDA, Director, OfficeofCivil Rights, Room326-W,Whitten Building, 14thand IndependenceAvenue,SW, Washington, DC,20250-9410, orcall (202)720-5964(voiceandTDD). USDAisanequalemploymentopportunityproviderandemployer. IDAHO WA TER SUPPL V OUTLOOK REPORT February 2003 1, SUMMARY Warm January temperatures resulted in rain falling at elevations over7,000 feet and getting much needed moisture back into the hydrologic cycle. But much more is needed. The lowest snowpacks are halfofnormal in the Spokane and Oakley basins. The lowest streamflow forecasts are in the high desert streams south ofthe Snake Riverand the Bear Riverat 30-50%ofaverage. The highest snowpacks are near normal with projected near normal streamflows in the Big Lost Riverbasin. With lessthan halfthe winter still to come, water users who rely on Idaho's snowfall remain optimistic still hoping forthe possibility ofmore winterstorms. But the odds of recovering to nearnormal or better levels by April 1 are slim based on historic data. Snow indices forseveral basins across the state illustrate that when February 1 snowpack was below average, the snow returned to near normal orbetterby April 1 only about 4 out of25 years. Only 1 ofthese 4 years, 1983, was an El Nino year like this year. Irrigation watershortages are expected across most ofsouthern and central Idaho especially with below normal future precipitation. SNOWPACK Rain above 7,000 feet melted some ofthe lower elevation snowpacks. Highersnow measuringstations retained some ofthe rainfall in the snow, and some drained out ofthe snowpack. The rainfall was a mixed blessing — it provided much needed moisture to Idaho, but would have helped the summer's water supply picture more ifit had all fell as snow. Currently, the lowest snowpacks in the state are about halfofnormal in the Coeurd'Alene, St. Joe, and Oakley basins. Next lowestare 55-65% ofaverage in the Bear River, Raft, Portneuf, Salmon Falls, Bruneau, Owyhee and North Fork Clearwaterbasins. Snowpacks in the 70-95%ofaverage include Pend Oreille, Clearwater, Salmon, Payette, Boise, Big Wood and upperSnake. The highest snowpacks remain in the Little Wood and Big Lost basins at 105%ofaverage. Snowpacks range from 40-65% oftheirApril 1 seasonal snow watercontent peaks with only40% ofthe winterstill to come. Warm January temperatures were the hot talk last month. ManyNWS valley and SNOTEL mountainous weather stations recorded nearorrecord high average monthly temperatures. New records set depends on length ofdata collected at each station. Jan. Avg. 2003 Jan. Avg. Station Basin Temp. Temp. Rank Lost Lake Clearwater 23 F 30 F T' warmestof 13 years Vienna Mine Salmon 17 25 T' warmest of 14 years Deadwood Summit Salmon 17 27 1st warmest of 14 years Mores Creek Sum Boise 32 23 l51warmest of 19 years Boise NWS Boise 30.2 38.7 5lh warmest of 139 years PocatelloNWS Snake 24.4 34.2 2nd warmest of 104 years Lewis Lake Div Yellowstone NP 17 25 1“warmest of 19 years Magic Mountain Salmon Falls 23 30 1” warmest of 13 years Emigrant Summit Bear 19 30 1“warmest of 13 years As a result ofthe rain and warm temperatures, some low elevation snow measuring sites are at or near record low values. From north to south: - Lookout SNOTEL site, located at 5,140 feet nearthe ski area, is the 3rd lowest since 1945. Only 1977 and 1981 had less. - Sherwin SNOTEL site, 3,200 feet, in the headwaters ofthe St. Maries/Potlatch rivers is 21% ofaverage with 1.8 inches ofsnow water; 2nd lowest since records started in 1960. - Pierce Ranger Station snow course in the Clearwaterbasin has 1.8 inches ofsnow water, average is 7.8 inches; 2nd lowest since 1951. - Bad Bear, 4,940 feet,just above Idaho City, and Bogus Basin Road, 5,540 feet, both in the Boise basin are the 4th and 5th lowest since records started in early 1960s. PRECIPITATION January precipitation wasthe greatest in the Clearwaterbasin at 135%ofaverage, normal in thewest central mountains, and 70-90%across central and eastern Idaho. Southern Idaho missed outon thestormsthattracked across central andnorthern Idaho. January precipitation was about45% ofaverage in the basinsstretching from the Owyhee basin tothe BearRiver. The lowestamountswereabout20%ofaverage in southern Idaho and headwaters ofthe BearRiverin Utah. These southern Idaho basins also hostthe lowestwateryearto date precipitation in the state at67% ofaverage. The highestwateryearto date precipitation is in the Salmon andwest central mountains at90% ofaverage. RESERVOIRS Reservoirstoragegota littleboast in January from the rain falling above 7,000 feet in elevation. Warm temperatures and rain melted some ofthe low andmid-elevation snowpacks and broughtstreams up across the western edge and parts ofcentral Idaho. Coeurd'Alene Lake increased from 33%to 60%ofits summercapacity during January. Dworshak Reservoirincreased from 63%to 68%ofcapacity and is now 109%ofaverage. The Payette reservoirsystem storage increased from 56%to 59%ofcapacity. All reservoirs and lakes from Cascade Reservoirnorth arenow storing average orabove storage levels. The Boise reservoirsystem increased from 33% to 38%ofcapacity and is now the same as ayearago. The Owyhee Reservoircame up from 16%to20%of capacity. Elsewherereservoirs in the state are 25-65% ofaverage. The increase in January streamflow from rain and some snowmeltinghelpedthe watersupply picture by getting much needed moistureback into thehydrologic picture— soil moisture, streamflow and reservoirstorage. In adry yearlike this, we'll take whateverwecan get. Ideally, it would be better ifall the precipitation fell as snow and remained in the mountainsto melt inthe springand summer, keepingthestreams higher in the summerwhen the consumptive use ofwaterand demand is greatest. Consumptive useofwater is least in winterwhenthe majority of Idaho's annual precipitation falls, andthe highest in summerwhen monthly precipitation amounts arethe least. In addition, havingthatJanuary precipitation fall as snowwouldhave provided much needed economic help for Idaho's winterrecreation. Note: NRCS reportsreservoir information in terms ofusablevolumes, which includesboth active, inactive and in some cases dead storage. Otheroperators may reportreservoircontents in differentterms. Foradditional information, seethe reservoirdefinitions in this report. STREAMFLOW Most streamflow forecasts decreased from a month ago. The highest forecasts call fornearnormal runoffinthe Big Lost Riverbasin. The lowestforecasts are in the BearRiverbasin at 32% ofaverage. Elsewhere across southern Idaho, streams are forecast for40-50% ofaverage forOakley Reservoir, Salmon Falls andOwyhee. The Bruneau Riverfairs slightly betterat57%. Upper Snake streams are forecastat60-80%ofaverage. Big Wood, Boise and Payette basins are forecastat 80-90%ofaverage. The Salmon is forecastat 86%ofaverage. Dworshak Reservoir inflow andthe St. Joe are forecastat 55-65%ofaverage. Pend Orielle Lake inflow is forecastat65% of average, while the northern Panhandletributaries are forecastare 85%ofaverage. To reducethe risk ofnothavingenough water, managers should considerusingthe 90% or 70% Chance Exceedance ProbabilityForecasts because ofthe dry soils, inefficiency ofthe snowpackto produce streamflow following dry years, belownormal snow levels and assumption ofnormal future precipitation inthe forecast equations. Based on the Surface WaterSupply Index (SWSI), irrigation watersupplieswill be adequate in the Boise basin ifthe 50% Exceedance Forecastoccurs. Shortages are likely acrosstherestofcentral, southern and eastern Idaho especially iffutureprecipitation is below normal. Magnitude ofshortages depends on yourwater right and watersource orsources. Waterusers should stay in contactwiththeirirrigation district formore specific information. RECREATION Warm temperatures andwinterprecipitation falling as rain inthe mountain is not helpingthewinterrecreation, but below freezingtemperatures in Idaho's centralmountainshas keptmostofthe precipitation falling as snow. The Big Wood, Little Wood and Big Lostbasinshostsome ofthebestsnow in the West. Summerwhitewateractivities in Idaho remains promisingas below normal snow levels often result in a shorterhigh waterseason and can extend the floating season on the lowerrivers. Headwaterstreamsmay run low again as aresult ofthe low snow. More snow and spring rains are needed in the Owyhee and Bruneau high desert streams. IDAHOSURFACE WATERSUPPLYINDEX(SWSI) As of February 1, 2003 The Surface Water Supply Index (SWSI) is a predictive indicatorofsurface wateravailability within a watershed for the spring and summer water use season. The index is calculated by combining pre-runoffreservoirstorage (carryover) with forecasts ofspring and summerstreamflow. SWSI values are scaled from +4. (abundant supply) 1 to -4. (extremely dry), with a value ofzero indicating a median watersupply as compared to historical 1 occurrences. SWSI values are published January through May and provide a more comprehensive outlook ofwateravailability than either streamflow forecasts orreservoirstorage figures alone. The SWSI index allows comparison ofwater availability between basins fordrought or flood severity analysis. Threshold SWSI values have been established for most basins to indicate the potential for agricultural watershortages. The following agencies and cooperators provide assistance in the preparation ofthe Surface Water Supply Index for Idaho: US National Weather Service US Army Corps ofEngineers US Bureau ofReclamation Idaho Dept, ofWater Resources Idaho Water Users Association PacifiCorp Agricultural Water MostRecent Year With SupplyShortageMay SWSI SimilarSWSI Value Occur WhenSWSIis BASINorREGION Value Less Than PANHANDLE NA -3.3 1987/94 CLEARWATER NA -2.2 1988 SALMON NA -0.8 1995 WEISER -1.4 2000 NA PAYETTE -1.0 2000 NA BOISE -2.0 1989 -2.6 WOOD BIG -1.2 2000 -1.4 LITTLE WOOD -0.5 1985 -2.6 BIG LOST -0.7 1985 -0.8 LITTLE LOST -2.5 2000 0.0 HENRYS FORK -2.0 1990/91 -3.3 SNAKE (HEISE) -2.9 1988 -2.3 OAKLEY -2.2 1988 0.0 SALMON FALLS -2.6 1990/91 0.0 BRUNEAU NA -1.9 1991 BEAR RIVER -3.9 2002 -3.8 SWSISCALE, PERCENTCHANCEOFEXCEEDANCE,AND INTERPRETATION -4 -3 -2 -1 0 1 2 3 4 _ 991% 871% 751% 63%1 501% 371% 251% 13%1 11% Much Below Near Normal Above Much IBelow | Normal 1 Water Supply | Normal | Above 1 I | 1 | | 1 Note: The Percent Chance ofExceedance is an indicatorofhow often a range ofSWSI values might be expected to occur. Each SWSI unit represents about 12% ofthe historical occurrences. As an example ofinterpreting the above scale, the SWSI can be expected to be greaterthan -3.0, 87% ofthe time and less than -3.0, 13%ofthe time. Halfthe time, the SWSI will be below and halfthe time above a value ofzero. The interval between -1.5 and +1.5 described as "Near Normal Water Supply," represents three SWSI units and would be expected to occurabout one-third (36%) ofthe time. Middle Fork Salmon River Basin Snow Index for Years 1963-2003 Banner, Deadwood & Morgan Creek SNOTEL Sites Water Snow of Inches 69 74 71 97 66 Boise Basin Snow index for Years 1 961 - 2003 Atlanta, Dollarhide, Graham Guard Station, Jackson Peak, Mores Creek, Trinity M ountain V ienna Mine , GSrnaosswy ILnakdee,xLfeowrisSnLaakkee, SRniavkeer RBiavseirnStaabtioovn,eTJhaucmkbsoDniviLdae,kea,ndWTywoforOcYeeaanrsSN1O9T6E1L-2s0i0te3s Year PANHANDLE REGION FEBRUARY 2003 1, Mountain Snowpack (inches) Mountain Precipitation PANHANDLE REGION PANHANDLE REGION WATER SUPPLY OUTLOOK January precipitation was 1 12% ofaverage. As a result, water year to date precipitation rose to 80%. The lowest snowpacks are only halfofaverage in the Coeur d'Alene, St. Joe and Spokane river basins. The Moyie and Priest basins fair better at 75% and 91% ofaverage, respectively. The lowest snowpack percentages are in the lower elevations south ofCoeur d'Alene Lake with some site near record low levels. Sherwin SNOTEL site, 3,200 feet, in the headwaters ofthe St. Maries/Potlatch rivers is 21% ofaverage with 1.8 inches ofsnow water; 2nd lowest since records start in 1960; only 1981 had less snow. Lookout SNOTEL site, located at 5,140 feet near the ski area, is the 3rd lowest since 1945. Only 1977 and 1981 had less. Overall, the Panhandle Region snowpack is 63% of average,just over halfoflast year's. The Pend Oreille river basin snowpack is 70% ofaverage, based on 70 snow measuring sites. Storage in the reservoirs and lakes got a boost last month with the winter rains in January. Current storage is above average for water storage facilities in Idaho and Montana. Lost Lake SNOTEL site at 6,1 10 feet along the St. Joe and North Fork Clearwater river basin divide, recorded its warmest average monthly January temperature for its 14 year data record. Streamflow forecasts decreased from last month and now range from 55-85% ofaverage. Water users should plan for and expect below normal runoffvolumes this summer PANHANDLE REGION Streamflow Forecasts - February 1, 2003 «=== Drier ====== Future Conditions ======= Wetter » Forecast Point Forecast Period 90% 70% 50% (Most Probable) 30% 10% 30-Yr Avg. (1000AF) (1000AF) (1000AF) (% AVG.) (1000AF) (1000AF) (1000AF) KOOTENAI at Leonia (1,2) APR-JUL 4030 4880 5270 75 5660 6510 7035 APR-SEP 5880 6020 6080 75 6140 6280 8125 MOYIE RIVER at Eastport APR-JUL 291 323 345 86 367 399 403 APR-SEP 304 337 360 86 383 416 418 SMITH CREEK APR-JUL 76 91 102 83 113 128 123 APR-SEP 77 94 106 82 118 135 129 BOUNDARY CREEK APR-JUL 82 97 107 87 117 132 123 APR-SEP 87 102 112 87 122 137 129 CLARK FK at Whitehorse Rpds (1,2) APR-JUL 3850 6220 7290 65 8360 10730 11280 APR-SEP 4230 6830 8010 64 9190 11790 12460 PEND OREILLE Lake Inflow (2) APR-JUL 5350 7110 8300 65 9490 11250 12700 APR-SEP 5830 7750 9060 65 10370 12290 13900 PRIEST near Priest River (1,2) APR-JUL 500 610 660 81 710 820 814 APR-SEP 415 615 705 81 795 1000 868 COEUR D'ALENE at Enaville APR-JUL 240 355 430 58 505 620 739 APR-SEP 260 375 455 59 535 650 778 ST. JOE at Calder APR-JUL 430 565 655 58 745 880 1136 APR-SEP 460 595 690 57 785 920 1205 SPOKANE near Post Falls (2) APR-JUL 790 1130 1370 54 1610 1950 2552 APR-SEP 825 1180 1420 54 1660 2020 2650 SPOKANE at Long Lake (2) APR-JUL 950 1350 1620 57 1890 2290 2851 APR-SEP 1080 1500 1780 58 2060 2480 3072 PANHANDLE REGION PANHANDLE REGION Reservoir Storage (1000 AF) - End of January Watershed Snowpack Analysis - February 1, 2003 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 2427.0 2503.0 2214.7 Kootenai ab Bonners Ferry 18 66 69 FLATHEAD LAKE 1791.0 1218.0 1181.0 971.2 Moyie River 7 78 75 NOXON RAPIDS 335.0 329.5 320.3 310.9 Priest River 4 77 91 PEND OREILLE 1561.3 943.5 577.0 749.3 Pend Oreille River 70 73 70 COEUR D'ALENE 238.5 142.5 115.0 115.6 Rathdrun Creek 4 36 59 PRIEST LAKE 119.3 64.0 63.7 55.5 Hayden Lake 0 0 0 Coeur d'Alene River 6 42 48 St. Joe River 3 46 54 Spokane River 12 39 50 Palouse River 1 15 21 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual volume will exceed the volumes in the table. The average is computed for the 1971-2000 base period. (1) - The values listed under the 10% and 90% Chance of Exceeding are actually 5% and 95% exceedance levels (2) - The value is natural volume - actual volume may be affected by upstream water management.