Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. aTD224.I2I33 Idaho Water Supply >55^ M \'v- I I Outlook Report UnitedStatesDepartmentofAgriculture Natural Resources ConservationService June 2011 1, Emigrant Summit SNOTEL (elevation 7390ft) Snow Water Equivalent Emigrant SNOTEL site has had above average snow water equivalent (SWE) all year long and the Bear River basin has some of the highest snowpacks on record. Since unseasonably cool temperatures caused snowpacks to linger unusually late in the season, the terminology in this report switches from “percent of average” to “percent of peak”. By switching the terminology, water users can compare the current snowpack to how much snow is present in an average winter. Once the 30 year average drops in the low numbers such as shown above, the percent of average results in numbers topping out in the thousands state wide, which can be confusing. At Emigrant SNOTEL, the SWE is “97% of the average peak” SWE, indicating that a typical winter’s worth of snowmelt is yet to come. At this point, how the snow melts is more of a concern than the amount. Consecutive hot days or rain on the melting high snowpack will cause higher waters in already swollen creeks and rivers. The best case scenario would be moderate temperatures to slowly melt the snowpack and no more precipitation so farmers can finally plant. Basin Outlook Reports and Federal - State - Private Snow Cooperative Surveys Formorewatersupplyandresoureemanagementinformation, orto subscribetothispublication Contact - - Your local county Natural Resources Conservation Service Office or Natural Resources Conservation Service Internet Web Address Snow Surveys http://www.id.nrcs.usda.aov/snow/ 9173 West Barnes Drive, Suite C Boise, Idaho 83709-1574 (208) 378-5740 To join a free email subscription list contact us by email at: [email protected] How forecasts are made Most ofthe annual streamflow inthe westernUnited States originates as snowfall thathas accumulatedin the mountains duringthe winterand early spring. As the snowpackaccumulates, hydrologists estimate the runoffthat will occurwhen itmelts. Measurements ofsnow water 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 preparerunoffforecasts. Unless otherwise specified, all forecasts are forflows that would occurnaturallywithout anyupstreaminfluences. Forecasts ofanykind, ofcourse, are notperfect. Streamflowforecast uncertainty arises fromthreeprimary sources: (1) uncertainknowledge offuture weather conditions, (2) uncertainty inthe forecastingprocedure, and (3) errors in the data. The forecast, therefore, mustbe interpretednot as a single value but rather as a range ofvalues with specificprobabilities ofoccurrence. The middle ofthe range is expressedbythe 50% exceedance probability forecast, forwhich there is a 50% chance thatthe actual flowwill be above, and a 50% chance thatthe actual flow willbe below, this value. To describe the expectedrange aroundthis 50% value, four otherforecasts are provided, two smallervalues (90% and 70% exceedance probability) andtwo largervalues (30%, and 10% exceedanceprobability). For example, there is a 90% chance that the actual flowwill be more than the 90% exceedance probabilityforecast. The others canbe interpreted similarly. The widerthe spread amongthese values, the more imcertain the forecast. As the season progresses, forecasts become more accurate, primarilybecause a greaterportion ofthe future weatherconditions become known; this is reflectedby a narrowing ofthe range around the 50% exceedance probability forecast. Users shouldtake this uncertainty into considerationwhen making operational decisions by selecting forecasts correspondingto the level ofrisktheyare willing to assume about the amount ofwaterto be expected. Ifusers anticipate receiving a lesser supply ofwater, or iftheywish to increase theirchances ofhaving an adequate supply ofwater fortheiroperations, theymaywant to base their decisions on the 90% or 70% exceedance probability forecasts, or something inbetween. Onthe otherhand, ifusers are concerned aboutreceiving too much water (for example, threat offlooding), theymaywant to base their decisions onthe 30% or 10% exceedance probability forecasts, or something inbetween. Regardless ofthe forecastvalue users choose for operations, they shouldbe 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 than this amount.) Byusingthe exceedance probability information, users can easily determine the chances ofreceiving more or less water. The U.S. DepartmentofAgriculture (USDA) prohibitsdiscrimination inall its programsandactivitiesonthe basisofrace, color, national origin, age, disability, andwhereapplicable, sex, marital status, familial status, parental status, religion, sexualorientation, geneticinformation, political beliefs, reprisal, orbecauseall ora partofan individual's incomeisderivedfrom anypublicassistanceprogram. (Notall prohibited basesapplytoall programs.) Personswith disabilitieswhorequirealternative meansforcommunicationofprogram information (Braille, large print, audiotape, etc.) should contactUSDA'sTARGETCenterat(202)720-2600 (voiceand TDD). Tofileacomplaintofdiscriminationwriteto USDA, Director, OfficeofCivil Rights, 1400 independenceAvenue, S.W., Washington, D.C. 20250-9410or call (800)795-3272 (voice)or(202)720-6382 (TDD). USDAisanequalopportunityproviderand employer.". IDAHO WATER SUPPLY OUTLOOK REPORT June 2011 1, SUMMARY The strong La Nina weather pattern that dominated our weather all winter has brought unseasonably cool temperatures this spring and added another month ortwo of snowfall to Idaho's mountains and slowed snowmelt in May. The result is one ofthe deepestJune 1 snowpacks ever measured in Idaho. The situation has provided more than enough waterfor all and created a potentially threatening runoff season. High damaging flows can still occur across most ofthe state since deep snowpacks are still present. The greatest concerns are in the Upper Snake and Bear River basins where flooding is occurring and will continue to occur as the high elevation snow melts. Late peaking snowpacks are an anomaly and it's important to understand how it impacts Idaho's water supply and runoff picture. In an average year up to about two-thirds ofthe snowpack melts during April and May. In fact that's the reason streamflow forecasts throughout the winter reference the April-July and April-September runoff period. This year April's streamflow was only halfofaverage in the headwater streams because cool temperatures prevented snowmelt. Despite continued cool temperatures in May, streamflows were above average but the peaks on most rivers are still to come. Looking forward not only do we have more snow than normal, but it will melt and run off in a shorter time period. The streamflow forecasts in this month's report are for the June-July and June-September periods and represent the residual runoff amounts left in the snowpack. Streamflowforecasts increased from last month and range from a low of 120-130% of average in the Salmon, Payette, Boise, Camas, Little Wood, Big Lost drainages to near 200% ofaverage in the Teton, Salt, Owyhee, Salmon Falls and NF Coeur d'Alene drainages, and a high of 318% for the Bear River below Stewart Dam. More water in less time means volumes will be much greaterthan normal. From this point, Idaho needs the right combination offuture weatherto relieve the pressure when the remaining higher elevation snow melts. The best case scenario would be for continued coolerthan normal temperatures, not record breaking heat, combined with dry weather for the rest ofJune. Moderate temperatures would allow the snow to continue melting at less than an inch a day; if melt rates increase to 1-2 inches a day the streams will also increase accordingly until more snow melts in the higher elevations. SNOWPACK On June 1, about 80 SNOTEL sites in Idaho and the watersheds that drain into the state were at or near record high June 1 snow water content levels. Another 30 sites were either melted out or at non- records forJune 1. A few snow measuring stations are actuallyjust reaching their peak snow water content amounts for the season; these include Two Ocean Plateau and Grand Targhee SNOTEL sites in the Snake River headwaters. June 1 snowpack percentages are high and should be used with caution as explained on the cover ofthis report. Snow indexes based on 10 sites in the Bear River show the snowpack is nearly twice the previous record high June 1 level that was measured in 1983. Similarly, the Teton basin snowpack records start in 1981, and this year's snow is higher than the previous maximum that occurred in 1983. The 18 station snow index in the Salmon River is the 2nd highest; only 1982, which is the yearthe records begin, had more snow water on June 1. Salmon Falls snowpack is also the 2nd highest; only 1984 had more snow on June 1. All June 1 snow indexes are available at this link for comparison to past years: http://www.id.nrcs.usda.gOv/snow/data/historic.html#snoindex PRECIPITATION May's weather pattern continued the trend of March and April by pumping above average precipitation amounts across most of Idaho. This has been the pattern forthe past three months, March, April and May. The pattern also featured a slight precipitation hole centered in Idaho's central mountains; where precipitation was less than other basins in January, April and May. This hole has actually turned into good news as it will provide a bit of high water reliefforthe Wood and Lost basins as the remaining snow melts. May precipitation amounts were 90-100% of average in the Big Lost and Little Wood basins, while the highest amounts were 170-180% of average in Salmon Falls, Goose Creek and Owyhee basins. The Bear River, Bruneau, eastern Idaho and Upper Snake in Wyoming, Boise and Weiser basins received 150-160%. Amounts were 115-140% ofaverage in the Panhandle, Clearwater, Salmon, Payette, Big Wood and Little Lost basins. Normal May precipitation amounts range from 2 to 5 inches across the state with the higher amounts in northern Idaho. With four months still to go this water year, 14 of Idaho's 21 major basins have already received their normal annual precipitation amounts since the start ofthe water year on October 1, 2010. The lowest amounts are in the headwaters streams in Idaho's central mountains at 85-95% oftheir normal annual totals while Idaho's southern basins have received the most at 115-140% oftheir annual amounts. RESERVOIRS Reservoir operators are managing the delicate balance between high inflows and safe outflows. They must ensure flood storage space is maintained until the peak runoff is past and that the impacts to downstream communities are minimized. Operators must also consider hydropower production and levees in their decision making process. Dworshak and Palisades reservoirs were nearly drained in anticipation ofthe high runoff. This year Bear Lake saw its second greatest November-May increase in storage since records begin in 1922, and could fill by fall. Bear Lake gained 400,000 acre-feet, second only to 1945-1946 when it increased 420,000 acre-feet between November and May. The lingering drought effects in the Bear basin may finally be over. Salmon Falls Reservoir is storing 133,700 acre- feet, capacity is 182,600 acre-feet and could still come close to filling ifthe 10% Chance Exceedance Forecast of 57,000 acre-feet forthe June-July period occurs. Oakley Reservoir is in a similar situation with 25,000 acre-feet left to fill and a 10% Chance of Exceedance Forecast of 20,000 acre-feet; keep in mind the simple calculations to not include releases for irrigation demand during the June-July period. Magic and Little Wood reservoirs are 90-95% full, while Mackay is 59% full. Owyhee is full and passing inflow. Coeur d'Alene and Priest lakes are 176% and 129% oftheir summer capacities respectively and are passing inflows until the snowmelt streamflow peaks occur. One additional note, the NRCS will be assisting the Army Corps of Engineers and Bureau of Reclamation in June on snowline reconnaissance flights to determine the final fill of Dworshak, as well as, reservoirs in the Boise and Upper Snake projects. Note: NRCS reports reservoir information in terms ofusable volumes, which includes both active, inactive and in some cases, dead storage. Other operators may report reservoir contents in different terms. Foradditional information, see the reservoir definitions in this report. STREAMFLOW Streamflow forecasts reflect the unusually high June 1 snowpacks and call for near record high June- September volumes in parts ofthe Upper Snake, Bear and Spokane rivers. The Teton River near Driggs is forecast at 285,000 acre-feet, 186% of average, same as 1997's runoff; the Snake River near Heise is forecast at 171% of average, just 200,000 acre-feet less than the 1997 volume. The Bear River below Stewart Dam is forecast at 430,000 acre-feet, 312% of average forJune-September, which is the same record high volume amount that occurred in 1983; records start in 1927. The Spokane River near Post Falls is forecast at 1,750,000 acre-feet, 226% of average, the third highest since 1914 and only exceeded by 1974 and 1916. Idaho's southern streams are forecast at 175-210% of average, these include: Goose, Salmon Falls, Bruneau and Owyhee. The lowest June-September forecasts are 115- 125% of average in the Little Wood and Big Lost basins. June -September residual runoff is forecast at 135-155% of average forthe Boise, Payette, Salmon and Clearwater streams. The Kootenai River and Pend Oreille Lake inflow are forecast at 145% and 177% of average, respectively. Users need to understand these regression forecasts rely on a limited number ofyears with such large June 1 snowpacks. Even so the equations are generally still reliable when the regression lines are extrapolated beyond the bulk ofthe observed data. Since the cool and wet trend is still present users should consider using the 30% and 10% Chance of Exceedance Forecast volumes to base their decisions on if it is not too late. Water decision makers should also be aware ofthe Daily Water Supply Forecast equations on this page: http://www.id.nrcs.usda.gov/snow/watersupply/daily guidance.html These daily forecasts track the changing water supply conditions and are performing very well. These graphs display all five chance of exceedance Forecasts. The "User Info" graphs also display cumulative flow to help users compare forecasted values with observed runoff. Note: Forecasts published in this report are NRCS forecasts. Jointly coordinated published forecasts bythe USDA NRCS and the NOAA NWS are available from thejointwest-wide WaterSupply Outlook forthe Western US at http://www.wcc.nrcs.usda.gov/wsf/westwide.html .The volumes referenced in these narratives are the 50% Chance of Exceeding Forecast, unless otherwise noted. Users may wish to use a different forecastto reduce their risk of havingtoo much ortoo little water. RECREATION River runners waiting for peak flows to pass will have to wait a little longer. Above normal precipitation has continued adding to the already huge snowpacks while cool temperatures slowed the melt. Fligher elevation snow measuring sites in the Upper Snake in Wyoming are just now reaching their peak snow water content. Here is what we know so far... Snow melt driven streamflow peaks have occurred in the Owyhee, Weiser and Camas Creek near Fairfield and most other lower elevation drainages across the state. Based on analysis of snowmelt driven peak flows and the amount of remaining snow, peak flows will not occur until the latter halfofJune for the Teton River and other tributaries fed from high elevation basins. With over 50 inches of snow water at several sites in the Bear River, those peak flows have not occurred yet. Streams with their headwaters in Idaho's central mountains (Big Wood, Big Lost, SF Boise, MF Salmon and SF Salmon) and other rivers across the state will see another increase from the remaining snow. Numerous factors will determine ifthe next peaks exceed the previous peaks. The potential for extreme flows can't be overstated because ofthe enormous June 1 snowpacks and the continued wet weather pattern. Cooler than normal temperatures, without more precipitation, are needed for another four weeks to gradually melt the snow and keep rivers relatively well behaved. Hot temperatures or rain during this critical time period when the snow is receding and soils are saturated, will send a flush ofwater down many streams and generate big flows. For current information on these snowmelt streamflow relationship analyses, view the snow-stream graphs and streamflow graphs on this page: http://www.id.nrcs.usda.gov/snow/watersupply/peakflow.html Ifyou can wait until after the peak flows have occurred, there will be an extended river running season that will provide family friendly floating levels well into the summer months. IDAHO SURFACE WATER SUPPLY INDEX (SWSI) June 1 2011 , The Surface WaterSupply Index (SWSI) is a predictive indicator ofsurface wateravailability within a watershed for the spring and summerwater use season. The index is calculated by combining pre-runoff reservoirstorage (carryover) with forecasts ofspring and summerstreamflow. SWSI values are scaled from +4.0 (abundant supply) to - 4.0 (extremely dry), with a value ofzero indicating a median water supply as compared to historical occurrences. The SWSI analysis period is from 1971 to present. SWSI values provide a more comprehensive outlook ofwater availability by combining streamflowforecasts and reservoir storage where appropriate. The SWSI index allows comparison ofwater availability between basins for drought orflood severity analysis. Threshold SWSI values have been determined forsome basins to indicatethe potential foragricultural irrigation water shortages. Agricultural Water MostRecent Year SupplyShortageMay SWSI WithSimilarSWSI Occur WhenSWSIis BASINorREGION Value Value Less Than Northern Panhandle 3.7 1999 NA Spokane 3.7 2008 NA Clearwater 2.4 1976 NA Salmon 2.4 1983 NA Weiser 2.0 1993 NA Payette 2.4 1997 NA Boise 1.6 1986 -2.4 Big Wood 2.3 1984 -1.0 Little Wood 1.0 2009 -2.2 Big Lost 1.5 2009 -0.2 Little Lost 3.0 1982 0.4 Teton 4.0 1997 NA Henrys Fork 4.0 1997 -3.4 Snake (Heise) 3.7 1997 -1.6 Oakley 2.6 2006 -0.8 Salmon Falls 3.5 1971/1972 -1.6 Bruneau 3.5 1971 NA Owyhee 3.3 1998 -3.0 Bear River 1.1 1973 -3.7 SI/I/S/SCALE, PERCENTCHANCEOFEXCEEDANCE,ANDINTERPRETATION —— — -4 -3 -2 -1 0 1 2 3 4 --- -1 -1 -1 1 1 1 , 1 1 99% 87% 75% 63% 50% 37% 25% 13% 1% Much Below Near Normal Above Much 1 1 1 1 1 1 Below Normal Water Supply Normal Above 1 1 1 1 1 1 NA = NotApplicable, Note; The PercentChance 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 exampleofinterpretingthe above scale,the SWSI can be expectedto be greaterthan -3.0, 87% ofthetime and less than -3.0, 13% ofthetime. Halfthetime,the SWSI will be belowand halfthetime above a value ofzero. The interval between -1.5 and +1.5 described as "Near Normal Water Supply," representsthree SWSI units and would be expectedto occurabout one-third (36%) ofthetime. PANHANDLE REGION JUNE 1 2011 , Mountain Precipitation PANHANDLE REGiON 0) D) ni o c ua> i_ (i> Q. Oct Nov Dec Jan Feb Mar Apr May It depends on which basin you look at in Idaho, who you talk to or which report you are referring to as to whether or not it is a record snowpack year. For example, 1997 had a higher peak snow amount than this year. 1997's snow melted faster than this year which means this year's June 1 snowpack has broken the late season snow record since measurements start in the early 1980s. There is still as much snow today as their usually is at the peak of a normal winter in mid-April. This year's long-lasting, deep snowpack is posing a threat for more flooding and extended high streamflows this summer. Heavy rains in late May increased the monthly precipitation amount to 138% ofaverage. The saturated conditions and full creeks have led to numerous flood warnings for the St. Joe, Spokane and St. Marie's rivers and the threat is not over as 7 feet or more of snow is left in the high country. The ideal situation would be cooler temperatures to slowly melt the snowpack, gradually decreasing the risk offlooding. Streamflow forecasts for the July-September period range from 145% of average for the Kootenai River and up to 210% for the St. Joe River. | PANHANDLE REGION * Streamflow Forecasts - June 1, 2011 „ . Future Cr-oiid1r'L-.•X iS 1 — Forecast Point Forecast 1 L.Ilance 01 Exceeding Period 90% 70% 50% 30% 10% 30-Yr Avg. 1 1 1 1 (lOOOAF) (lOOOAF) (lOOOAI") (% AVG.) (lOOOAF) (lOOOAF) (lOOOAF) 1 1 1 1 .... ..... Kootenai R at Leonia (1,2) JUN-JUL 5127 5720 1 5990 153 1 6260 6853 3920 1 1 JUN-SEP 6209 6932 7260 145 7588 8311 5000 1 1 1 1 Moyie River at Eastport JUN“iJUXj 221 247 265 183 283 309 145 1 1 JUN-SEP 237 266 285 178 304 333 160 1 1 1 1 Smith Ck nr Porthill JUN“JUXi 85 96 104 208 112 124 50 1 1 JUN-SEP 89 104 114 204 124 139 56 1 1 1 1 Boundary Ck nr Porthill 65 74 80 174 86 95 46 1 1 JUN-SEP 71 81 88 169 95 105 52 1 1 1 1 Clark Fork at Whitehorse Rpds (1,2) JUN~iJUXj 9212 9960 10300 183 10640 11388 5620 1 1 JUN-SEP 10604 11495 11900 176 12305 13196 6750 1 1 1 1 Pend Oreille Lake Inflow (2) JUN-JUL 10225 10806 11200 183 11594 12175 6120 1 1 JUN-SEP 11728 12426 12900 177 13374 14072 7280 1 1 Priest R nr Priest River (1,2) JUN-JUL 425 495 1 525 181 555 625 290 1 1 JUN-SEP 470 550 590 171 630 710 345 1 1 NF Coeur d'Alene R at Enaville JUN~JUXi 312 337 1 355 223 1 373 398 159 1 1 JUN-SEP 349 380 400 202 420 451 198 1 1 St. Joe R at Calder JUN-JUL 748 812 1 855 225 1 898 962 380 1 1 JUN-SEP 833 900 945 210 990 1057 450 1 1 Spokane R nr Post Falls (2) JUN“JUXj 1446 1532 1 1590 236 1 1648 1734 675 1 1 JUN-SEP 1556 1672 1750 226 1828 1944 775 1 1 Spokane R at Long Lake (2) JUN“JUXj 1660 1755 1 1820 217 1 1885 1980 840 1 1 JUN-SEP 1907 2040 2130 201 2220 2353 1060 1 1 1 1 PANHANDLE REGION PANHANDLE REGION 1 Reservoir Storage (1000 AF) - End of May Watershed Snowpack Analysis - June 1, 2011 1 Usable *** Usable Storage *** Number This Year as % of Reservoir Capacity| This Last 1 Watershed of 1 Year Year Avg Data Sites Last Yr Average 1 1 HUNGRY HORSE 3451.0 1749.0 2999.0 2588.0-1 Kootenai ab Bonners Ferry 8 257 231 1 FLATHEAD LAKE 1791.0 1506.0 1531.0 1499.2 1 Moyie River 1 291 227 1 I NOXON RAPIDS 335.0 326.8 323.7 313.6 Priest River 2 246 224 1 1 PEND OREILLE 1561.3 588.2 1243.9 1333.1 Pend Oreille River 44 227 226 1 1 COEUR D'ALENE 238.5 418.8 229.0 270.4 Rathdrum Creek 1 0 0 1 1 PRIEST LAKE 119.3 153.6 126.4 138.5 Hayden Lake 0 0 0 1 1 Coeur d'Alene River 4 686 304 1 1 St. Joe River 4 333 203 1 1 Spokane River 9 454 253 1 1 Palouse River 1 0 0 1 1 * 90%, 70%, 50%, 30%, and 10% chances of exceeding are the probabilities that the actual volume will exceed the volumes in the table. The average is cortputed 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. (3) - Median value used in place of average.