Table Of Content

Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. Basin Outlook Reports and Federal - State - Private Cooperative Snow Surveys For more watersupply and resource management information, contact: Local Soil Conservation Service Field Office or william weiier Water Supply Specialist Soil Conservation Service W. 316 Boone Ave; Suite 450 Spokane, WA 99201 (509) 353-2341 How forecasts are made Most of the annual streamflow in the Western United States originates as snowfall that has accumulated high in the mountains during winter and early spring. As the snowpack accumulates, hydrologists estimate the runoff that will occur when it melts. Predictions are based on careful measurements of snow water equivalent at selected index points. Precipitation, temperature, soil moisture and antecedent streamflow data are combined with snowpack data to prepare runoff forecasts. Streamflow forecasts are coordinated by Soil Conservation Service and National Weather Service hydrologists. This report presents a comprehensive picture of water supply conditions for areas dependent upon surface runoff. It includes selected streamflow forecasts, summarized snowpack and precipitation data, reservoir storage data, and narratives describing current conditions. Snowpack data are obtained by using a combination of manual and automated SNOTEL measurement methods. Manual readings of snow depth and water equivalent are taken at locations called snow courses on a monthy or semi-monthly schedule during the winter. In addition, snow water equivalent, precipitation and temperature are monitored on a daily basis and transmitted via meteor burst telemetry to central data collection facilities. Both monthy and daily data are used to project snowmelt runoff. Forecast uncertainty originates from two sources: (1) uncertainty of future hydrologic and climatic conditions, and (2) error in the forecasting procedure. To express the uncertainty in the most probable forecast, four additional forecasts are provided. The actual streamflow can be expected to exceed the most probable forecast 50% of the time. Similarly, the actual streamflow volume can be expected to exceed the 90% forecast volume 90% of the time. The same is true for the 70%, 30%, and 10% forecasts. Generally, the 90% and 70% forecasts reflect drier than normal hydrologic and climatic conditions; the 30% and 10% forecasts reflect wetter than normal conditions. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty will become known and the additional forecasts will move closer to the most probable forecast. All programs and services ofthe USDA Soil Conservation Service are offered on a nondiscriminatory basis, without regard to race, color, national origin, religion, sex, age, marital status, or handicap. 3TlIASil3S C!K sayo33a "iviyys iNsyyno Ayyyaii ^inoiy^v ivNoiiyH 3ynimo;i:a3y 30 u.d3ci *s 0801-1.0366 VM‘0ue>|ods 09C UJOou M episjOAiu 036 eo|Ajes uo|}eAjesuo3 nos Vi ejn^nouSv i )o )UdLuyedeQ S0}b;S poiiufl sijoddu >|oouno ujseg In addition to basin outlook r#>orts, aWater Supply Forecast forthe Western United States is published bythe Soil Conservation Serviceand National Weather Service monthly, Januarythrough May. Reports may be obtained fromthe Soil Conservatiorj Service, Vj/est NationalTechnical CenAter,'511 Northwest Broadway, Room 248, Portland, OR — 9720-9-3489. ^ '' Issuedby Released by William (Bill) Richards Lynn A. Brown Chief State Conservationist Soil Conservation Service Soil Conservation Service U.S. Department of Agriculture Spokane, Washington TURN OVER FOR MAILING ADDRESS — Using the forecasts an example Using the MostProbable Forecast. Using the example forecasts shown below, users can reasonably expect 36,000 acre-feet to flow past the gaging station on the Mary’s River near Deeth between March 1 and July 31. Using the HigherExceedance Forecasts. Ifusers anticipate a somewhat drier trend in the future (monthly,and seasonal weatheroutlooks are available from the National Weather Service every two weeks), or if they are operating at a level where an unexpected shortage ofwatercould cause problems, they might want to plan on receivingonly 20,(XX) acre-feet (from the 70 percent chance ofexceeding forecast). In seven out often years with similarconditions, streamflow volumes will exceed the 20,(X)0 acre-foot forecast. Ifusers anticipate extremely dry conditions forthe remainderofthe season, orifthey determine therisk of using the70 percentchance ofexceeding forecast is too great, then they might plan on receiving only 5000 acre-feet (from the 90 percentchance ofexceeding forecast). Nine outoften years with similarconditions, streamflow volumes will exceed the 5000 acre-foot forecast. Using theLowerExceedanceForecasts. Ifusers expect wetterfuture conditions, or ifthe chance that five out ofevery ten years with similarconditions wouldproduce streamflow volumes greaterthan 36,000 acre-feet was more than they would like torisk, they mightplan on receiving 52,000 acre-feet (from the 30 percent chance of exceeding forecast) to minimize potential flooding problems. Three outoften years with similarconditions, streamflows will exceed the 52,000 acre-foot forecast. In years when users expect extremely wet conditions forthe remainderofthe season and the threat ofsevere flooding anddownstream damage exists, they might choose to use the 76,000 acre-foot (10 percent chance of exceeding) forecastfortheir water management operations. Streamflow volumes will exceed this level only one yearout often. UPPERHUMBOLDTRIVERBASIN STREAMFLOWFORECASTS < DRIER FUTURECONDITIONS WETTER > I I I I FORECASTPOINT FORECAST ChanceofExceeding I 1 PERIOD 90% 70% 50%(MostProbable) 30% 10% 25 YR. I I I I (lOOOAF) (lOOOAF)l(lOOOAF) (%AVG.)I (lOOOAF) (lOOOAF)! (lOOOAF) I MARY’S RIVERnrDeeth MAR-IUL 5.0 20.0 36 77 52 76 47 1 1 APR-lUL 8.0 17.0 31 74 45 67 42 1 1 11 11 LAMOILLECREEKnrLamoille MAR-IUL 6.0 16.0 24 79 32 43 31 1 1 APR-IUL 4.0 15.0 22 75 30 41 30 1 1 11 I1 NFHUMBOLDTRIVER atDevilsGate MAR-IUL 6.0 12.0 1 43 73 1 74 121 59 Formore information concerning streamflowforecasting askyourlocal SCSfieldofficefora copy of"A Field Office GuideforInterpreting SteamflowForecasts". 2 Interpreting Streamflow Forecasts Introduction Each month, five forecasts are issued foreach forecast point and each forecast period. Unless otherwise specified, all streamflow forecasts are for streamflow volumes that would occur naturally without any upstream influences. Water users need to know what the different forecasts represent ifthey are to use the information correctly when making operational decisions. The following is an explanation ofeach ofthe forecasts. MostProbable (50 PercentChance ofExceeding) Forecast This forecast is the best estimate ofstreamflow volume that can beproduced given currentconditions and basedon the outcome ofsimilarpast situations. There is a 50 percent chance that the streamflow volume will exceed this forecast value. There is a 50 percent chance that the streamflow volume will be less than this forecast value. The most probable forecast will rarely be exactly right, due to errors resulting from future weather conditions and the forecast equation itself. This does not mean that users should not use the most probable forecast; it means that they need to evaluate existing circumstances and determine the amount ofrisk they are willing to take by accepting this forecast value. To Decrease the Chance ofHaving Too Little Water Ifusers want to make sure there is enough water available for theiroperations, they might determine that a 50 percentchance ofthe streamflow volume being lower than the most probable forecast is too much risk to take. Toreduce the risk ofnot having enough water available during the forecast period, users can base their operational decisions on one ofthe forecasts with a greaterchance ofbeing exceeded (orpossibly some point in-between). These include: 70PercentChance ofExceedingForecast There is a 70 percent chance that the streamflow volume will exceed this forecast value. There is a 30 percent chance the streamflow volume will be less than this forecast value. 90PercentChance ofExceedingForecast There is a90 percent chance that the streamflow volume will exceed this forecast value. There is a 10 percentchance the streamflow volume will be less than this forecast value. To Decrease the Chance ofHaving Too Much Water Ifusers want to make sure they don’t have too much water, they might determine that a 50percent chance ofthe streamflow being higher than the mostprobable forecast is too much ofa risk to take. Toreduce the risk of having too much water available during the forecast period, users can base theiroperational decisions on one of the forecasts with a smallerchance ofbeing exceeded. These include: 30PercentChance ofExceedingForecast There is a 30 percent chance that the streamflow volume will exceed this forecast value. There is a 70 percent chance the streamflow volume will be less than this forecast value. 10PercentChance ofExceedingForecast There is a 10 percent chance that the streamflow volume will exceed this forecast value. There is a 90 percentchance the streamflow volume will be less than this forecast value. 1 —— ———— 5 5 9 DATA CURRENT AS OF! 1/ 8/91 ?:26:A7 8ASIN SUMMARY OF SNOW COURSE DATA JANUARY 1991 SNOU COURSE ELEVATION DATE SNOW WATER LAST AVERAGE SNOW COURSE ELEVATION DATE SNOW WATER LAST AVERAGE DEPTH CONTENT YEAR 1961-83 DEPTH CONTENT YEAR 1961-83 PEND OREILLE RIVER YAKIMA RIVER DENTON MEADOW 2370 12/27/90 —e 1.3 .3 3.0 AHTANUM R.S. 3100 1/02/91 —7 1.3 .0 3.6 BENTON SPRING 4920 12/27/90 —24 5.5 2.3 8.6 BIG BOULDER CREEK 3200 12/28/90 40 8.0 2.4 7.2 BUNCHCRASS MEADOWS 5000 1/01/91 14.5E 8.0 14.6 BLEWETT PASS#2PILL0W 4270 1/01/91 6.4S .8 11.5 BUNCHCRASS MOWPILLOW 5000 1/01/91 — 14.7 8.—5 13.2 BUMPING LAKE 3450 12/28/90 —12 3.0 .0 6.5 HEART LAKE TRAIL 4800 1/01/91 —- 12.9E — 9,2 BUMPING LAKE <NEW) 3400 12/28/90 —15 3.6 .0 8.0 HOODOO BASIN 6050 1/01/91 31.9E — 21.3 BUMPING RIDGE PILLOW 4600 1/01/91 8.6S .3 11.0 HOODOO CREEK 5900 1/01/91 — 26.9E 19.1 CORRAL PASS PILLOW 6000 1/01/91 — 16.2S 4.7 15.5 LOOKOUT 5140 12/27/90 57 12.8 7.3 14.3 FISH LAKE 3370 12/28/90 —54 12.0 2.5 12.4 SCHWEITZER RIDGE 6200 1/01/91 20.7E 10.6 21.3 FISH LAKE PILLOW 3370 1/01/91 — 13.4S 4.5 15.1 GREEN LAKE PILLOW 6000 1/01/91 7.5S .3 8.7 KETTLE RIVER CROUSE CAMP PILLOW 5380 1/01/91 — 5.OS 3.1 9.0 LAKE CLE ELUM 2200 12/27/90 —12 3.1 .0 4.2 BARNES CREEK CAN. 5300 1/04/91 54 14.3 8.7 MORSE LAKE PILLOW 5400 1/01/91 — 17,3S 7.1 22.0 BIG WHITE MTN CAN. 5510 12/31/90 45 10.9 6.6 7.2 OLALLIE E.S. PILLOW 3960 1/01/91 — 20.1S 4.2 28.7 MFOANRARSOHNEE PASS CCAANN.. 44500000 121//0341//9910 2348 59..43 1.8 69..2 SSTAASSMEPEDREIDGPEASS PPIILLLLOOWW 43826000 11//0011//9911 — 1180..3SSS 76..16 1185..34 1UNNEL AVENUE 2450 12/27/90 25 6.3 1.0 8.7 COLVILLE RIVER WHITE PASS ES PILLOW 4500 1/01/91 9.IS .0 10.4 AHTANUM CREEK OMAK LAKE* THIN LAKES — AHTANUM R.S. 3100 1/02/91 7 1.3 .0 3.6 GREEN LAKE PILLOW 6000 1/01/91 7.5S .5 8.7 SPOKANE RIVER MILL CREEK — ABOVE BURKE 41CC 1/01/91 10.0£ 3.0 8.4 — FOURTH OF JULY SUM 3200 12/27/90 —18 3.0 .0 3.7 HIGH RIDGE PILLOW 4980 1/01/91 6.9S 12.2 LLOOSOTKOULTAKE 56111400 121//0217//9910 ——57 3132..87E 137..33 2154..25 LEWIS - COWLITZ RIVERS MSSSMUUOHONNSESSSQRQEEUWUTTIIITNTOO RIDGEPPIILLLLOOWW 53555552224400000000 11111/////0000011311/////9999911111 ——**2 211106736.....94442EE 158901.....4469 111145677.....17016 PJLPIUOAGNNRTEEAADIILPLSAIEKNEPEEPAAKRK PPPPIIIILLLLLLLLOOOOWWWW 5533958200000000 1111////00001111////99991111 ———-- 22310830....69IISSSS 1501...•7481 23111061....2906 POTATO HILL PILLOW 4500 1/01/91 — 9.5S 3.0 12.6 NEWMAN LAKE — SSHPEEENPCERCANMYOWON PPIILLLLOOWW 34400500 11//0011//9911 199..4OSS 11..57 1181..17 QUARTZ PEAK PILLOW 4700 1/01/91 7.1 4.0 -- SSPUIRRPIRTISELAKLEKS PPIILLLLOOWW 34120500 11//0011//9911 -— 183..96SS 5.•80 213..96 OKANOGAN RIVER WHITE PASS ES PILLOW 4500 1/01/91 9.IS •0 10.4 BRENDA MINE CAN. 4800 1/02/91 35 6.6 2.3 6.5 WHITE RIVER HHEGAANRRMOETIEYSLRBTBAOYCPNKASSHRIELSL PILCCCLAAANNNO...W 6654582109020000 111221////03031211////99991100 -593190 2312927....030SS 114822....8232 217838-...4126 CMCOOORRRSRREAALLLAPPKAAESSSS PPIILLLLOOWW 656040000000 111///000112///999111 ——58 111768,..732SS 74..17 2I2S.*05 IMSCICNUTLOLKOCHLAKE CCAANN.. 54520000 121//2028//9910 2256 54..06 2..09 33..52 GREEN RIVER WSSMMSMHTIUAIO.ILMLSNTVMMSAEEEOSIKRRNHO0LENR8EAOAMSNCUOTCOKWARPSSREAERSEKSMMSTTNNPICLCCCCCAAAAALANNNNNNO......W 4646455050295800000000000000 111221111///////02030002181034///////99999991111100 —624532112780 118959333...,...164843S 11402011....—..868279 116314867.......4635920 LSCGLSTYTHRAEOINAAWSUNNMSMTGPSIEAELRCRLDLAAMEMKCOMPERRTUNIEPN.DEATGKSAESINPPII4L2LLLOOWW 4342343817091260000000000000 1111111///////00000002212221///////99999991111111 —3344163022 11116490370.......88008S4SS 7321.....•.8798005 1116570489.......1348366 METHOW RIVER — CEDAR RIVER — HARTS PASS PILLOW 6500 1/01/91 32.5S 14.8 27.2 SALMON MOWS PILLOW 4500 1/01/91 3.3S 1.9 7.0 SNOOUALMIE RIVER CHELAN LAKE BASIN — 21BS6 IS NOT ON FILE LYMAN LAKE PILLOW 5900 1/01/91 —— 52.IS 18.4 28—.3 OLALLIE E.S. PILLOW 3960 1/01/91 20.IS 4.2 28,7 PMAIRNKERSCKRIRDIGDEGEPPIILLLLOOWW 64260000 11//0011//9911 — 4238..94SS 185..39 20.6 SKYKOMISH RIVER RAINY PASS PILLOW 4780 1/01/91 28.9S 9.8 23.2 — STAMPEDE PASS PILLOW 3860 1/01/91 16.SS 7.8 18.3 ENTIAT RIVER STEVENS PASS PILLOW 4070 1/01/91 20.9S 6.9 18.9 STEVENS PASS SAND SO 3700 12/28/90 56 12.6 6.7 19.3 POPE RIDGE PILLOW 3540 1/01/92 ... 7.5S 2.9 7,4 SKAGIT RIVER WENATCHEE RIVER HARTS PASS PILLOW 6500 1/01/91 — 32.SS 14.8 27.2 BCLHEIWWEATUTKUMPASG.SSt.2PILL0W 42520700 112//0218//9910 ——22 62..84S 1..28 151..05 LRYAMIANNY LPAAKSES PPIILLLLOOWW 54970800 11//0011//9911 - 2582..19SS 198..48 2283..32 FISH LAKE PILLOW 3370 1/01/91 13.4S 4.5 15.1 LYMAN LAKE PILLOW 5900 1/01/91 — 52.IS 18.4 28,3 BAKER RIVER MERRITT 2140 12/28/90 25 4.8 1.5 “.5 SUSTPTTRPEEOEVVUREECNNMSSWH«2EPPEAASSLSSERSPPPANIIIDLLLLLLOOOSWWWO 3544473000170000 12111////20008111.///99991110 ——56 210421....6479SSS 66...700 115889..,.1093 MDEJMTOAAA.CSRSKYTPEBENLRPBUAUMSTLPSTAAKESES AAAAAHMMMM 55353486820000000000 11111/////0000022222/////9999911111 111116206428086 5543423659.....00000 ————-- 3222315869.....64686 SQUILCHUCK CREEK ROCKY CREEK AM 2100 1/02/91 78 23.0 12.2 SCHREIBERS MOW AM 3400 1/02/91 87 28.0 — 22.8 SF THUNDER CK AM 2200 1/02/91 30 10.0 — 4.8 STEMILT CREEK — WATSON LAKES AM 4500 1/02/91 102 33.0 25.1 UPPER WHEELER PILLOW 4400 1/01/91 4.4S .0 8.0 QUILCENE RIVER — - COLOCKUM CREEK — MOUNT CRAG PILLOW 4050 1/01/91 6.2S 1.0 TROUGH »2 PILLOW 5310 1/01/91 1.7S .0 5.1 HYNOOCHEE RIVER CARROL PASS 3650 1/01/91 36 9.6 .0 11.0 U.S. DEPARTMENT OF WATERSHED AGRICULTURE BOUNDARY SOIL CONSERVATION 0>3 om> X U) SERVICE fOOs'j PRECIPITATION: State wide, December precipitation from National Weather Service stations was 68% of average. December precipitation varied from 106% of average in the Olympic Basin, to 60% in the Okanogan Basin. The year-to-date precipitation varied from 166% of normal in the North Puget Basin to 71% in the Colville-Pend Oreille Basin. SNOTEL sites in Washington showed the high elevation year-to-date precipitation values to be 131% of average. Maximum year-to-date precipitation was at the Olallie Meadows SNOTEL site near Snoqualmie Pass with 84.4 inches since October 1,1990, normal for this site would be 46.9 inches. RESERVOIRS: Above normal precipitation for the year-to-date has many of the states reservoirs spilling water for flood control. Reservoir storage is good and varies with reservoirs in the Cascade Mountains above average for Januai7 1 and those on the east side ofthe state below , average. Reservoir storage in the Yakima Basin was 764,900 acre feet, 129% of normal. Storage at other reservoirs include Roosevelt at 94% of average and the Okanogan reservoirs contain 133% of January 1 normal. The power reservoirs contain the following: Coeur d'Alene % Lake, 167,200 acre feet, or 81 of normal, and spilling; Chelan Lake, 591,200 acre feet at 156% of average and 87% of capacity, and Ross Lake at 161% of average, and spilling for the past two months. STREAMFLOW: December streamflows were generally above average in Washington. Streamflows were the following percent of normal, the Cowlitz River, 84%, the Walla Walla River, 72%; the Spokane River, 130%; the Columbia at the Canadian border, 131%. The Ckanogan River with 231% and the Methow with 206% had the largest percent of normal. Streamflow forecasts varie from 159% of average for the Smilkameen River to 71% of normal on Mill Creek in the Walla Walla River basin. January forecasts for some west side streams include: Cedar River, 103%; Skagit River, 122%; and the Dungeness River, 102%. Some east side streams include the Yakima River at Parker 116%; the Wenatchee River at Peshastin 138% and the Ckanogan River, 152%. . JANUARY 1991 GENERAL OUTLOOK SUMMARY: DECEMBER TEMPERATURES WERE BELOW NORMAL AND VARIED FROM 12 DEGREES BELOW IN THE OKANOGAN BASIN TO 4 DEGREE BELOW AVERAGE IN THE WALLA WALLA BASIN. THE SNOWPACK IS NEAR NORMAL STATE WIDE BUT VARIES FROM 63% IN THE WALLA WALLA BASIN TO 152% IN THE CHELAN BASIN. DECEMBER PRECIPITATION WAS 68% OF NORMAL STATE WIDE, AND VARIED FROM 60% OF AVERAGE IN THE OKANOGAN BASIN TO 106% IN THE OLYMPIC BASIN. YEAR TO DATE PRECIPITATION VARIES FROM 71% IN THE COLVILLE TO 166% IN THE NORTH PUGET. WASHINGTON'S SNOTEL SITES ARE AVERAGING 99% OF NORMAL SNOWPACK ON JANUARY (BY JANUARY 1 8. THE STATEWIDE AVERAGE WAS 96%). JANUARY 1 RESERVOIR STORAGE IS GENERALLY GOOD THROUGHOUT THE STATE, WITH RESERVOIRS IN THE YAKIMA BASIN AT 131% OF AVERAGE AND 72% OF CAPACITY. DECEMBER STREAMFLOWS VARIED FROM 231% OF NORMAL ON THE OKANOGAN RIVER TO 71% ON THE YAKIMA RIVER AT MARTIN. FORECASTS FOR 1991 RUNOFF VARY FROM 159% OF AVERAGE FOR SMILKAMEEN RIVER TO 71% ON MILL CREEK IN THE WALLA WALLA BASIN. SNOWPACK: SNOTEL sites in Washington are showing snowpack that is 99% of average for January 1 state wide. Snowpack varies over the state from 152% of normal i,n the Chelan Basin to 63% in the Walla Walla River Basin. The Yakima Basin is now at 79%. Snowpack in other basins along the west slopes of the Cascade Mountains are the Green with 97% and the Cowlitz Basin with 101%. The eastern slopes of the Cascade Mountains show the Wenatchee Basin at 108% of normal, and the Spokane at 102%. Maximum snow cover is at the Lyman Lake SNOTEL, in the Chelan Basin, with 52.1 inches of water content. This site would normally have 28.3 inches of water content on January 1