natural resources conservation service idaho water supply outlook report february 1, 2017 ·...

Natural Resources Conservation Service

Idaho Water Supply Outlook Report February 1, 2017

How many tons of snow are on your roof? An estimated 228 tons of snow water was on this onion storage barn in Weiser, Idaho. These pictures were taken January 28 and 29 while clearing the snow off Vaughn Youngberg’s family barn. The snow depth on the windblown side of the roof was measured at 30 inches deep with 9 inches of snow water. The natural snow measured on the ground on the east and west sides of Weiser on January 25 was 25 inches deep with 7.5 inches of snow water. The flat roof on the left was cleared twice with a snow blower and had an estimated 88 tons of snow on it. Most of the snow on the right side of the roof was cleared with shovels and had an estimated 70 tons of snow. The middle section, with another 70 tons of snow has not been cleared. If you know the inches of water in the snowpack and multiply by 5.2 (the conversion factor as explained on this Snow Load Info page) you will know the pounds per square foot of snow on your roof. Hopefully, this barn was saved from collapsing, but there have been a number of roof failures in southwest Idaho and southeast Oregon and more storms forecast in early February.

https://www.nrcs.usda.gov/wps/portal/nrcs/detail/id/snow/products/?cid=nrcs144p2_046673

For more water supply and resource management information:

Contact: Your local county Natural Resources Conservation Service Office Internet Web Address: http://www.id.nrcs.usda.gov/snow/ Natural Resources Conservation Service Snow Surveys 9173 West Barnes Drive, Suite C Boise, Idaho 83709-1574 (208) 378-5700 ext. 5

To join a free email subscription list contact us by email at: [email protected]

Water Supply Outlook Report Federal - State – Private Cooperative Snow Surveys

How forecasts are made Most of the annual streamflow in the western United States originates as snowfall that has accumulated in the mountains during the winter and early spring. As the snowpack accumulates, hydrologists estimate the runoff that will occur when the snow melts. Measurements of snow water equivalent at selected manual snow courses and automated SNOTEL sites, along with precipitation, antecedent streamflow, and indices of the El Niño / Southern Oscillation are used in computerized statistical and simulation models to produce runoff forecasts. Unless otherwise specified, all forecasts are for flows that would occur naturally without any upstream influences. Forecasts of any kind, of course, are not perfect. Streamflow forecast uncertainty arises from three primary sources: (1) uncertain knowledge of future weather conditions, (2) uncertainty in the forecasting procedure, and (3) errors in the data. The forecast, therefore, must be interpreted not as a single value but rather as a range of values with specific probabilities of occurrence. The middle of the range is expressed by the 50% exceedance probability forecast, for which there is a 50% chance that the actual flow will be above, and a 50% chance that the actual flow will be below, this value. To describe the expected range around this 50% value, four other forecasts are provided, two smaller values (90% and 70% exceedance probability) and two larger values (30%, and 10% exceedance probability). For example, there is a 90% chance that the actual flow will be more than the 90% exceedance probability forecast. The others can be interpreted similarly. The wider the spread among these values, the more uncertainty is in the forecast. As the season progresses, forecasts become more accurate, primarily because a greater portion of the future weather conditions become known; this is reflected by a narrowing of the range around the 50% exceedance probability forecast. Users should take this uncertainty into consideration when making operational decisions by selecting forecasts corresponding to the level of risk they are willing to assume about the amount of water to be expected. If users anticipate receiving a lesser supply of water, or if they wish to increase their chances of having an adequate supply of water for their operations, they may want to base their decisions on the 90% or 70% exceedance probability forecasts, or something in between. On the other hand, if users are concerned about receiving too much water (for example, threat of flooding), they may want to base their decisions on the 30% or 10% exceedance probability forecasts, or something in between. Regardless of the forecast value users choose for operations, they should be prepared to deal with either more or less water. (Users should remember that even if the 90% exceedance probability forecast is used, there is still a 10% chance of receiving less than this amount.) By using the exceedance probability information, users can easily determine the chances of receiving more or less water.

USDA is an equal opportunity provider and employer. To file a complaint of discrimination, write: USDA, Office of the Assistant Secretary for Civil Rights, Office of Adjudication, 1400 Independence Ave., SW, Washington, DC 20250-9410 or call (866) 632-9992 (Toll-free Customer Service), (800) 877-8339 (Local or Federal relay), (866) 377-8642 (Relay voice users).

http://www.id.nrcs.usda.gov/snow/

mailto:[email protected]

IDAHO WATER SUPPLY OUTLOOK REPORT

February 1, 2017

SUMMARY

The stage is set, and more winter weather is about to roll into Idaho the first full weekend in February. We’ll tell you what we know; including the variability of conditions across Idaho and how important it is to understand the fall and current hydro-climate information that created the current conditions in your basin. The abundant snowfall in many valley locations across the state combined with cold temperatures has resulted in minimal valley snowmelt between storms. Resulting, there’s increased concern regarding valley snowmelt with the approaching weather systems.

Statewide February 1 summary: • Panhandle Region – record high fall rains, normal low elevation snow and below normal high

elevation snow, which is approaching record low levels at a few site. • The Salmon River is the dividing line with below normal snow to the north and average or

greater to the south. • Weiser & Payette basins – well above average valley snow, below normal mountain snow.• Boise to Big Lost basins – above average low elevation snow while higher elevations are

average or greater.• Owyhee to Oakley/Raft basins – above average valley and high elevation snow.• Eastern Idaho, Snake above Palisades and Bear River – well above average low elevation

snow with above to well above average in the Bear River.• Henrys Fork – near normal snow in the south decreasing to below normal snow amounts to the

north towards Montana and Mud Lake area.

As mentioned last month, it is important to watch snow totals in your basin, freezing level (which may approach 7,000 feet in the Boise Mountains the first full week of February, storm intensity and precipitation phase (rain vs snow) which reveals where precipitation falls and if it adds to our mountain snowpack.

SNOWPACK

This year’s snowpack looks excellent, especially if you are at home looking out your windows. But don’t be fooled by thinking our mountain snowpack numbers reflect the valley snow outside your partially buried house. Abundant snowfall in the valley this year and cold temperatures across the state has largely prevented valley snowpacks from melting between storms. This has allowed nearly the whole state of Idaho to be covered by snow at the end of January. People are asking how the valleys can have so much snow and the mountains are only near normal in the Weiser and Payette basins. Those old snow surveyors who placed many of the snow measuring sites that are still used today were on a mission to find the state’s key snow accumulation zones. Those are the zones that represent the key areas that store winter snowpack and produces our annual streamflow. As a result of that early mission, there are very few locations that measure snow water content in the valleys.

Idaho residents have reported valley snow depth and we've made a few measurements of the valley snowpack across the state that are interesting to share. There was about a foot and half of snow in Spokane that has settled but has not melted yet; similar to the snow and ice reported in Bonners Ferry. Two miles north of Coeur d’Alene

14 inches of snow was measured with 3 inches of liquid water content. The McCall snow site has 37 inches of depth with 9.0 inches of water. On January 25, snow was measured on the east and west side of Weiser which had 25 inches of snow depth with 7.4 inches of water. Boise has had 1 inch of snow on the ground for over 50 days. This is tied for the 5th longest consecutive day stretch with an inch or more of snow on the ground. The record is 63 days set in 1986, snowfall records start in 1942. The February 1 measurement at the Ketchum Ranger Station showed the snow is 34 inches deep with 8.3 inches of water. On February 2, Pocatello had 10 inches of snow depth with a water content of 5 inches, and Montpelier had 23 inches snow on the ground.

Below is an excellent example of the manual and automated snow measurements for February 1, 2017, in the Weiser basin illustrating the extremely high snow water content levels in the lower, but not higher elevations.

Snowpacks vary across Idaho, so check your basin closely. The lowest snowpacks in our region are 65-70% of median in the Kootenai, Priest, Coeur d’Alene, and Spokane basins. The highest snowpacks are 155-170% of median in the Bear, Smiths Fork, Malad, Hoback, Portneuf, Bruneau and Owyhee basins. Elsewhere across the state, snowpacks vary with elevation, so consider individual sites and their elevations to better understand what may happen when the snow melts. You should also note how the October rains may have impacted your basin and may influence the runoff and in the spring. For example, the rain increased soil moisture throughout the state. In northern Idaho, the rain may have already left the basin while in the Big Lost basin the increase in baseflows is still noticeable.

PRECIPITATION

Idaho’s Salmon River was the dividing point for January’s jet stream and general storm track that brought well below normal precipitation to the north and up to twice normal January amounts south of the river. January precipitation was the lowest – at only 31% to 39% of average – in the Lochsa, Kootenai and Coeur d’Alene basins, respectively. The highest monthly percentages were 200% to 250% of average in the Bear River, Malad, Portneuf, Bruneau, Jarbidge and Camas Creek basins. January precipitation was 130% to 185% of average in the Boise, Big Wood, Little Wood, Big Lost, Hoback, Greys, Willow, Blackfoot, Goose, Salmon Falls and Owyhee basins. Mountain precipitation in January in the Weiser and Payette basins was 110% and 116% of average, respectively. Bear in mind, these SNOTEL sites are measurements of the mountain precipitation typically above 5,000 feet in elevation. The populated valleys across the state have received unusually high snowfall amounts and cold temperatures have kept the snow on the valley floor and ice in some rivers. Concerns are

mounting if a rapid melt or a rain on snow event occurs. Weather modeling shows that situation is approaching the first full week in February. Even with below normal precipitation for three consecutive months, amazingly, the water year to date precipitation is still above average at 113% in the Panhandle Region. This illustrates how much precipitation fell in October 2016 to start the water year. Only the Clearwater basin is now hosting below normal water year to date precipitation at 95% of average. The higher water year to date precipitation totals are 150% to 160% of average in the Bruneau. Bear and parts of central and eastern Idaho; these high water year to date precipitation totals are equivalent to about two-thirds of the annual precipitation that normally falls in 12 months. This means these basins received a lot of precipitation the first four months of this water year. The abundant October precipitation likely saturated soils across most of the state, and soils are still frozen in some areas due to cold temperatures. This may reduce soil moisture infiltration capacity if a sudden warm spell or rain on snow event occurs. Come spring, less water may be needed to fill the soil moisture profile and will likely increase overland flow increasing streamflow. RESERVOIRS Reservoirs are in good shape across Idaho and ready to catch the snow when it melts. Most reservoirs increased slightly in storage from a month ago which is typical during the winter. Major changes include Brownlee Reservoir, which was drafted during January due to cold temperatures and high power loads. It is now in good shape to reach their anticipated flood control targets. Mackay Reservoir, which may still be feeling the impacts from the fall precipitation, increased during January from 34,000 acre-feet to 38,400 acre-feet and is currently 148% of average, 86% of capacity. Little Wood Reservoir also increased from 67% of capacity to 79% by month’s end and is starting to release water. It is important to remember most of these large reservoirs are designed and operate to catch and store runoff from the mid- and higher-elevations in their watershed. People have asked what happens to all the low elevation snow when it melts. With minimum storage facilities in the lower elevations, this snow has the potential to melt and runoff rapidly across most of the state that is below 5,000 feet in elevation. The likelihood for rain that is forecast in early February increases these concerns for rapid runoff. This is why it is important keep drains and culverts open to help the water drain away from homes, and flow to the nearest street gutter or drain and on to the next tributary. STREAMFLOW Current streamflow forecasts mirror the snowpack across the state with the usual variability. The lowest forecasts are in the NF Coeur d’ Alene basin at 56% of average and increase to 65% for the Spokane River at Long Lake. In contrast, the highest ones are more than 200% of average in the Owyhee and Bear basins. Streams forecast in the 140% to 175% of average range include the Big Wood, Little Wood, Willow Creek, Portneuf, Salmon Fall, Bruneau and the Snake River near Heise along with a few upper Snake River tributaries. Forecasts in the West-Central Mountains call for 122% of average for the Boise River, 101% for the Payette River and 80% for the Weiser River. Please note, most of these streamflow target periods are for the April through July period and do not include the lower elevation runoff before April 1.

Because of the variable conditions across Idaho this year, streamflow forecast uncertainty, and with 40 percent of the winter still to come, water users should review and consider the impacts from all 5 exceedance streamflow forecasts. Specifically, if the dry trend continues in northern Idaho, those users should consider using the drier forecasts, while southern Idaho users should consider using the wetter forecasts if the current wet trend continues. Based on Idaho’s Surface Water Supply Index (SWSI), shortages are not expected at this time. Reservoir releases may be required depending upon how much moisture falls as rain or snow and how much of the low elevation snow melts from early February storms. Note: The volumes referenced in these narratives are the 50% Chance of Exceeding Forecast, unless otherwise noted. Users may wish to use a different forecast to reduce their risk of having too much or too little water. RECREATION For the winter recreationists, check your local avalanche conditions before heading to the backcountry. Remember, the goal is to return home to ski or ride another day. For the river runners, Idaho’s snowpacks and January 1 streamflow forecasts range from below normal in northern Idaho, normal in the Salmon to well above normal in Idaho’s southern corner basins – the Owyhee and Bear rivers. Stay tuned, keep those skis and sleds tuned, and get those boats ready if you are an early season boater. Joint Meeting of the Western Snow Conference & Weather Modification Association Registration and call for papers is open. Please join us on April 17-20, 2017 for a joint meeting of the 85th Annual Western Snow Conference and the Weather Modification Association in Boise, Idaho. The conference venue offers the opportunity to interact with other professionals while enjoying one of the most vibrant cities in the Intermountain West. http://www.westernsnowconference.org/ This first ever combined conference with the Weather Modification Association will kick off with a Monday afternoon short course entitled "Tracing the Effects of Cloud Seeding through the Hydrologic Cycle". Tuesday will begin with a joint plenary session, followed by concurrent sessions of oral and poster presentations. On Thursday, a technical tour will include a visit to the Dry Creek Experimental Watershed, a NRCS SNOTEL site, and a collaborative weather station for youth education.

https://www.nrcs.usda.gov/wps/portal/nrcs/detail/id/snow/waterproducts/?cid=stelprdb1240689

https://www.nrcs.usda.gov/wps/portal/nrcs/detail/id/snow/waterproducts/?cid=stelprdb1240689

http://www.avalanche.org/

http://www.westernsnowconference.org/

IDAHO SURFACE WATER SUPPLY INDEX (SWSI) February 1, 2017 The Surface Water Supply Index (SWSI) is a predictive indicator of surface water availability within a watershed for the spring and summer water use season. The index is calculated by combining pre-runoff reservoir storage (carryover) with forecasts of spring and summer streamflow. SWSI values are scaled from +4.0 (abundant supply) to -4.0 (extremely dry), with a value of zero indicating a median water supply as compared to historical occurrences. The SWSI analysis period is from 1981 to present. SWSI values provide a more comprehensive outlook of water availability by combining streamflow forecasts and reservoir storage where appropriate. The SWSI index allows comparison of water availability between basins for drought or flood severity analysis. Threshold SWSI values have been determined for some basins to indicate the potential for agricultural irrigation water shortages.

BASIN or REGION

SWSI Value

Most Recent Year With Similar SWSI

Value

Agricultural Water Supply Shortage May Occur When

SWSI is Less Than

Spokane -2.9

2005 NA Clearwater -1.1 2013 NA

Salmon 0.5 2010

NA Weiser -0.7

2016 NA Payette 0.7

2010 NA Boise 1.6

2012 -1.5

Big Wood 2.0

1996 0.8 Little Wood 2.5 1998

-1.2

Big Lost 2.5 2006 0.8

Little Lost 1.8 2011 1.5 Teton 2.0 1999 -3.9

Henrys Fork 2.3

2008 -1.7 Snake (Heise) 2.3

1998 -1.7 Oakley 1.6 2007 0.6

Salmon Falls 2.0 2006 -0.8 Bruneau 3.4 2006 NA Owyhee 2.9 2011

-2.6 Bear River 0.9

1988 -3.7

SWSI SCALE, PERCENT CHANCE OF EXCEEDANCE, AND INTERPRETATION

-4 -3 -2 -1 0 1 2 3 4 |------|------|------|------|------|------|------|------|

99% 87% 75% 63% 50% 37% 25% 13% 1% ------------------------------------------------------------------------ |Much | Below | Near Normal | Above | Much | |Below | Normal | Water Supply | Normal | Above | ---------------------------------------------------------------------- NA=Not Available / Not Applicable; Note: The Percent Chance of Exceedance is an indicator of how often a range of SWSI values might be expected to occur. Each SWSI unit represents about 12% of the historical occurrences. As an example of interpreting the above scale, the SWSI can be expected to be greater than -3.0, 87% of the time and less than -3.0, 13% of the time. Half the time, the SWSI will be below and half the time above a value of zero. The interval between -1.5 and +1.5 described as "Near Normal Water Supply," represents three SWSI units and would be expected to occur about one-third (36%) of the time.

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SALMON RIVERBASINS

SOUTHSIDE SNAKERIVER BASINS

PANHANDLE REGION

CLEARWATER BASIN

BEAR RIVER BASIN

UPPER SNAKE RIVER BASIN

WEST CENTRAL

BASINS

WOOD & LOST BASINS

Copyright:© 2014 Esri

0 50 100 150 20025Miles

¯

This map is prepared by the USDA-NRCS Idaho Snow Survey Office. http://www.nrcs.usda.gov/wps/portal/nrcs/main/id/snow/

Water Supply Forecast February 1, 2017

Forecasted April to July Flow as a Percentage of the 1981 to 2010 Average

Provisional Data - Subject to Revision

#* > 180%#* 150 - 179%#* 130 - 149%#* 110 - 129%") 90 - 109%

#*70 - 89%#*

50 - 69%#*

25 - 49%#*

0 - 24%( No Data

AverageForecast

Above Average

BelowAverage

SALMON RIVERBASINS


PANHANDLE REGION

CLEARWATER BASIN

BEAR RIVER BASIN


WEST CENTRAL

BASINS

WOOD & LOST BASINS

163

162

118

68

76

154

100

81

74

63

127

86

105

123

125

119

155

79

161

164

133

67

10587

108

119

123

132

110111

132

123

70

83

113

158129

126126

89

134

101

73


0 50 100 150 20025Miles

¯


Percent of Median SnowpackFebruary 1, 2017

Basin-wide Snow Water Equivilant as a Percentage of the 1981 to 2010 Median

MedianSnowpack

Above

Below


>= 150%130 - 149%110 - 129%90 - 109%70 - 89%50 -69%0 - 49%No Data

SALMON RIVERBASINS


PANHANDLE REGION

CLEARWATER BASIN

BEAR RIVER BASIN


WEST CENTRAL

BASINS

WOOD & LOST BASINS

186

215

145

36

39

199

118

54

52

39

166

111

112

98

11096

173

35

168

171

209

161

52

93

104

152

105

182

118

155

155

132

49

89

164

53

203166

173128

73

184

38


0 50 100 150 20025Miles

¯


Monthly Precipitation January 2017 Monthly Precipitation as a

Percentage of the 1981 to 2010 Average


>= 150%130 - 149%110 - 129%90 - 109%70 - 89%50 -69%0 - 49%No Data

AveragePrecipitation

Above

Below

SALMON RIVERBASINS


PANHANDLE REGION

CLEARWATER BASIN

BEAR RIVER BASIN


WEST CENTRAL

BASINS

WOOD & LOST BASINS

137

160

138

93

113

152

112

95

136

103

100

97

138

141

101

171

91

152

149

162

124

12197

149

129

144

154

115

147

148

138

116

96

123

156 150

122154

105

152

106

124

126


0 50 100 150 20025Miles

¯


Water Year to Date Precipitation February 1, 2017

Basin-wide Water Year Precipitation as a Percentage of the 1981 to 2010 Average


>= 150%130 - 149%110 - 129%90 - 109%70 - 89%50 -69%0 - 49%No Data

AveragePrecipitation

Above

Below

Panhandle Region February 1, 2017

WATER SUPPLY OUTLOOK

Precipitation and Snowpack

January precipitation was much below average in the Panhandle, ranging from 36% of average in the Kootenai River drainage to 52% of average in the St. Joe. Even after below average precipitation for the third consecutive month, water year to date precipitation is still above average at about 110%. Unfortunately, the current snowpack numbers reveal that most of the water year precipitation came in October and as rain instead of snow. Snowpack is below normal throughout the Panhandle Region at about 70% of median, except for the Palouse River drainage, which is 101% of median.

Storage and Streamflow Forecasts

Lake Coeur d’Alene is 48% of average, while Lake Pend Oreille and Priest Lake are 78% and 80% of average, respectively. Streamflow forecasts have decreased and call for below normal to near normal volumes ranging from 55-90% of average in these northern Idaho basins. Water supplies should still be adequate based on these February 1 streamflow forecasts, but if the dry trend continues, water users should monitor the changing water supply forecasts.

Priest Lake 45.6 54.2 56.7 119.3Lake Coeur d' Alene 46.3 114.1 96.3 238.5

Noxon Rapids Reservoir 321.0 324.5 315.0 335.0Lake Pend Oreille 589.1 629.3 753.9 1561.3

Hungry Horse Lake 3021.5 2523.5 2375.0 3451.0Flathead Lake 925.5 990.7 955.6 1791.0

Kootenai ab Bonners Ferry 14 68% 89%

Reservoir Storage (KAF): End of January

Reservoir Name Current (KAF) Last YR Average

(KAF)Capacity

(KAF)

Spokane River 14 70% 87%Palouse River 2 101% 104%

Coeur d' Alene River 6 63% 74%St. Joe River 4 74% 89%

Priest River 5 67% 100%Rathdrum Creek 4 76% 109%

Basin Name # of Sites

% of Median2017 2016

Moyie River 5 73% 99%

2540 2850Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions

Watershed Snowpack Analysis: February 1, 2017

1960 2360 2620APR-SEP 1160 1570 1850 65% 2130

Spokane R at Long Lake APR-JUL 995 1400 1680 64%

2390APR-SEP 905 1270 1520 61% 1770 2140 2480

1090 1120Spokane R nr Post Falls 2 APR-JUL 845 1210 1460 61% 1710 2080

885 1020 1050APR-SEP 645 775 865 77% 955

St. Joe R at Calder 2 APR-JUL 585 715 800 76%

700APR-SEP 200 330 415 56% 505 635 740

920 830NF Coeur dAlene R at Enaville APR-JUL 172 300 390 56% 475 605

765 865 780APR-SEP 560 665 740 89% 815

Priest R nr Priest River 2 APR-JUL 535 635 700 90%

11800APR-SEP 9400 10700 11600 91% 12500 13800 12800

13100 11500Pend Oreille Lake Inflow 2 APR-JUL 8520 9760 10600 90% 11400 12700

10200 11900 10500APR-SEP 7800 9620 10400 90% 11300

Clark Fork R at Whitehorse Rapids 1 & 2 APR-JUL 6950 8660 9440 90%

117APR-SEP 63 78 88 72% 98 112 123

8090 7590Boundary Ck nr Porthill APR-JUL 61 75 84 72% 94 108

6430 7270 6600APR-SEP 5750 6550 6920 91% 7290

Kootenai R at Leonia 1 & 2 APR-JUL 4830 5670 6050 92%

375APR-SEP 245 300 335 87% 370 425 385

10%(KAF)

30yr Avg(KAF)

Moyie R at Eastport APR-JUL 235 285 325 87% 360 410

Panhandle Region Streamflow Forecasts - February 1, 2017Forecast Exceedance Probabilities for Risk Assessment

<--Drier-------------------Projected Volume-------------------Wetter-->

Forecast Point Forecast Period

90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

Clearwater River Basin February 1, 2017



After above normal precipitation fell to finish off the 2016 calendar year in the Clearwater basin, precipitation was much below normal in January at about half of normal monthly precipitation, and water year to date precipitation is 95% of average. Snowpack is below normal at 80% of median in the Clearwater basin as a whole.


Dworshak Reservoir is 98% of average, which is 66% of capacity. Streamflow forecasts have decreased since January 1st, and are now hovering around 90% of average for all forecast points except for Dworshak Reservoir inflow, which is forecast at 81% of average volume. As of February 1, near normal to slightly below normal water supplies are expected.


(KAF)Capacity

(KAF)Dworshak Reservoir 2297.8 2347.1 2335.0 3468.0

Selway River 4 81% 93%Clearwater Basin Total 17 80% 95%

NF Clearwater River 8 76% 94%Lochsa River 3 79% 92%

Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions





6890APR-SEP 4790 5740 6390 88% 7030 7990 7270

5180 4540Clearwater R at Spalding 2 APR-JUL 4490 5420 6040 88% 6670 7600

4340 4940 4310APR-SEP 3110 3730 4140 91% 4560

Clearwater R at Orofino APR-JUL 2930 3530 3930 91%

2410APR-SEP 1560 1880 2100 82% 2320 2640 2570

1630 1480Dworshak Reservoir Inflow 2 APR-JUL 1430 1750 1960 81% 2180 2500

1390 1560 1410APR-SEP 1050 1220 1340 91% 1450

Lochsa R nr Lowell APR-JUL 990 1160 1270 90%

1920APR-SEP 1450 1690 1850 92% 2010 2250 2020

10%(KAF)

30yr Avg(KAF)

Selway R nr Lowell APR-JUL 1370 1600 1760 92% 1920 2150

Clearwater River Basin Streamflow Forecasts - February 1, 2017Forecast Exceedance Probabilities for Risk Assessment



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

Salmon River Basin February 1, 2017



The Salmon River basin received a large spatial variation in precipitation during January, and has generally been observed as the cutoff for the much wetter than normal southern half of the state and the much drier than normal northern half of the state during January. As a whole, the Salmon River basin received about 100% of average precipitation during January. The upper most Salmon River areas received 150-175% of average precipitation, while only 50-75% of average precipitation was observed lower in the system during January. Water year to date precipitation is 109% of average. Snowpack, similar to the precipitation trend outlined above, is greater in the upper most Salmon River. Snowpack in the Salmon River basin as a whole is 96% of median.


Streamflow forecasts call for near normal to above normal volumes ranging from 100-125% of average in the Salmon River and its tributaries. As of February 1, water supplies should be adequate for the water users and river runners.

Salmon Basin Total 24 96% 117%

SF Salmon River 3 86% 111%Little Salmon River 4 83% 131%

Lemhi River 7 105% 119%MF Salmon River 3 100% 118%



Salmon River ab Salmon 7 118% 118%

7830 5940Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions


6170 7080 5370APR-SEP 4440 5450 6140 103% 6820

Salmon R at White Bird APR-JUL 4020 4930 5550 103%

191APR-SEP 157 186 205 100% 225 255 205

365 290Johnson Ck at Yellow Pine Id APR-JUL 143 171 190 99% 210 235

300 345 270APR-SEP 215 260 290 100% 320

Sf Salmon R nr Krassel Ranger Station APR-JUL 197 240 270 100%

690APR-SEP 595 770 895 116% 1010 1190 770

148 90MF Salmon R at MF Lodge APR-JUL 535 695 805 117% 915 1070

98 125 74APR-SEP 60 82 99 110% 117

Lemhi R nr Lemhi APR-JUL 47 67 82 111%

775APR-SEP 815 1000 1120 124% 1250 1430 900

10%(KAF)

30yr Avg(KAF)

Salmon R at Salmon APR-JUL 715 870 975 126% 1080 1240

Salmon River Streamflow Forecasts - February 1, 2017Forecast Exceedance Probabilities for Risk Assessment



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

West Central Basins

February 1, 2017



The Boise River basin continues to get the bulk of the precipitation from storm events in the West Central basins, receiving 163% of average precipitation during January, while the Payette and Weiser River basins received 116% and 110%, respectively. Water year to date precipitation ranges from 100-125% of average. Snowpack ranges from 90-130% of median across the West Central basins. The Weiser River basin has a notable and impressive low elevation snowpack, with snow measurements in the 4,000-4,500 ft. range that are 300-500% of median! Paradoxically, the Weiser River basin snowpack above 5,500 ft. is lower than normal, ranging from 70-95% of median.


Reservoir storage in the Boise system is 102% of average, 54% of capacity, while the Payette system is 99% of average, 63% of capacity. Streamflow forecasts call for below normal volumes (80% of average) in the Weiser basin and increase to above average (115-125% of average) in the Boise basin. As of February 1, water supplies are promising based on good fall precipitation, current snowpack, and Surface Water Supply Indexes which are above shortage thresholds.

Mann Creek Reservoir 1.1 1.8 3.6 11.1

Sub-Basin Total 540.7 471.4 543.4 855.1Lake Lowell 92.4 98.6 92.8 165.2

Deadwood Reservoir 95.0 72.2 87.9 161.9Cascade Reservoir 445.6 399.2 455.5 693.2

Lucky Peak Reservoir 80.7 88.5 103.5 293.2Sub-Basin Total 546.2 515.0 534.7 1015.6

Anderson Ranch Reservoir 254.3 229.6 256.4 450.2Arrowrock Reservoir 211.2 196.9 174.8 272.2

Weiser Basin Total 7 125% 117%



(KAF)Capacity

(KAF)

Payette Basin Total 16 98% 121%Mann Creek 1 94% 152%

NF Payette River 9 87% 120%SF Payette River 5 111% 123%

Canyon Creek 4 196% 139%Boise Basin Total 17 126% 125%

MF & NF Boise Rivers 6 113% 119%Mores Creek 4 126% 125%



SF Boise River 8 133% 127%

510 400Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.

1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions


360 480 370APR-SEP 167 250 315 79% 390APR-JUL 151 230 290 78%

1630Weiser R nr Weiser FEB-JUL 260 390 495 80% 610 800 615

1860 1480APR-SEP 1150 1400 1580 97% 1760 2010

152 173 131Payette R nr Horseshoe Bend 2 APR-JUL 1140 1350 1500 101% 1650

APR-SEP 103 124 138 105%

455Deadwood Reservoir Inflow 2 APR-JUL 97 116 129 105% 142 161 123

600 400APR-SEP 410 480 530 116% 585 670

605 715 640SF Payette R at Lowman APR-JUL 360 425 475 119% 520

APR-SEP 345 455 530 83%

495NF Payette R nr Banks 2 APR-JUL 390 490 560 90% 630 730 625

575 485APR-SEP 270 360 415 84% 475 565

78 89 83NF Payette R at Cascade 2 APR-JUL 295 380 435 90% 495

APR-SEP 55 64 71 86%

1360Lake Fork Payette R nr McCall APR-JUL 53 62 69 86% 76 86 80

1920 1260APR-SEP 1280 1500 1660 122% 1810 2040

163 205 119Boise R nr Boise 2 APR-JUL 1160 1390 1540 122% 1690

APR-SEP 83 114 137 115%

635Mores Ck nr Arrowrock Dam APR-JUL 80 109 132 115% 156 197 115

855 585APR-SEP 580 685 755 119% 820 925

690 790 510Boise R nr Twin Springs APR-JUL 535 630 695 119% 760

APR-SEP 460 560 625 123%

30yr Avg(KAF)

SF Boise R at Anderson Ranch Dam 2 APR-JUL 430 525 590 124% 650 745 475



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

10%(KAF)

West Central Basins Streamflow Forecasts - February 1, 2017Forecast Exceedance Probabilities for Risk Assessment

Wood & Lost River Basin February 1, 2017

WATER SUPPLY OUTLOOK Precipitation and Snowpack

Monthly precipitation was above normal again in the Wood & Lost River basins, and generally ranged from 120-185% of average in these basins, with the highest amounts in the Little Wood River basin (184%) and lowest in the Little Lost basin (118%). Drainages farthest to the east received the least precipitation. Water year to date precipitation still ranges from 130-160% of average in all Wood and Lost River basins. Similar to precipitation observations, there’s less snow relative to normal in the eastern most drainages, where near normal snow conditions exist (Camas-Beaver Creeks and Birch-Medicine Lodge Creeks). However, snowpack is above normal in the Little Lost, Big Lost, Fish Creek, Little Wood, Big Wood, and Camas Creek drainages. Camas Creek and Fish Creek drainages are currently the highest, at 158% and 163% of median.


Reservoir storage is above average with Mackay Reservoir at 148% of average (86% of capacity), Little Wood Reservoir at 145% of average (79% of capacity), and Magic Reservoir at 127% of average (46% of capacity). Streamflow forecasts generally range from 130-160% of average, except for Camas Creek at Camas, which is forecast at 114% of average. As of February 1, water surplus is much more of a concern than water shortages as releases are now starting from Little Wood Reservoir

Little Wood Reservoir 23.6 11.4 16.3 30.0Magic Reservoir 87.5 32.9 68.9 191.5


(KAF)Capacity

(KAF)Mackay Reservoir 38.4 27.0 26.0 44.4

Camas Creek 5 158% 141%Big Wood Basin Total 12 135% 126%

Little Wood River 4 134% 111%Big Wood River ab Hailey 7 123% 118%

Big Lost Basin Total 7 119% 101%Fish Creek 3 163% 98%

Little Lost River 3 110% 108%Big Lost River ab Mackay 6 123% 101%

Camas-Beaver Creeks 4 89% 108%Birch-Medicine Lodge Creeks 2 108% 116%






250APR-SEP 235 340 410 155% 480 585 265

220 83Big Wood R bl Magic Dam 2 APR-JUL 230 325 395 158% 465 565

166 220 82APR-SEP 70 106 135 163% 167

Camas Ck nr Blaine APR-JUL 69 105 134 163%

170APR-SEP 169 240 285 157% 335 400 182

475 265Big Wood R ab Magic Reservoir APR-JUL 162 225 270 159% 315 380

370 425 235APR-SEP 255 320 365 138% 410

Big Wood R at Hailey APR-JUL 230 290 330 140%

92APR-JUL 60 93 115 149% 137 170 77

184 86MAR-SEP 73 109 134 146% 159 195

126 155 69Little Wood R nr Carey 2 MAR-JUL 69 103 126 147% 150

APR-JUL 57 86 106 154%

77MAR-SEP 69 101 123 150% 145 178 82

285 150Little Wood R ab High Five Ck MAR-JUL 65 95 115 149% 136 166

196 240 123APR-SEP 117 168 200 133% 235

Big Lost R bl Mackay Reservoir APR-JUL 92 136 166 135%

159APR-SEP 151 200 235 131% 265 315 180

57 34Big Lost R at Howell Ranch APR-JUL 135 178 205 129% 235 280

39 46 28APR-SEP 28 37 43 126% 48

Little Lost R nr Howe APR-JUL 24 30 35 125%

30yr Avg(KAF)

Camas Ck at Camas APR-JUL 11.8 24 32 114% 40 53 28

Forecast Exceedance Probabilities for Risk Assessment<--Drier-------------------Projected Volume-------------------Wetter-->


90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

10%(KAF)

Wood and Lost Basins Streamflow Forecasts - February 1, 2017

Upper Snake River Basin February 1, 2017



Precipitation was above average for the second consecutive month, with individual basins generally receiving 130-170% of average. Less precipitation was observed in the Henrys Fork and Teton River drainages (105-115%). Water year to date precipitation ranges from 140-170% of average in these Upper Snake basins. Snowpack ranges from 100-160% of median in the Upper Snake basins, with greater amounts higher up in the system and in southeastern Idaho (Portnuef, Blackfoot, Willow Creek). As a whole, the Snake River above American Falls snowpack is 132% of median.


Combined reservoir storage for Palisades and Jackson Lake is 89% of average, and 53% of capacity. Overall, the 8 major reservoirs are 96% of average, and 60% of capacity. Streamflow forecasts generally range from 125-165% of average in the Upper Snake River basin, with lessor amounts forecast for the Henrys Fork and Falls River (~110%). As of February 1, water supplies look promising for the numerous water users that rely on the Upper Snake River.

Basin-Wide Total 2761.2 2682.3 2865.4 4577.9

Blackfoot Reservoir 219.7 173.6 176.3 337.0American Falls Reservoir 1115.5 919.1 1116.0 1672.6

Sub-Basin Total 184.2 186.6 192.0 240.8Ririe Reservoir 48.4 45.8 38.7 80.5

Island Park Reservoir 87.7 96.7 100.0 135.2Grassy Lake 14.1 13.1 11.9 15.2

Sub-Basin Total 1193.4 1357.2 1342.4 2247.0Henrys Lake 82.4 76.8 80.1 90.4

Jackson Lake 555.1 563.6 431.2 847.0Palisades Reservoir 638.3 793.6 911.2 1400.0

Snake River ab American Falls 50 132% 99%



(KAF)Capacity

(KAF)

Blackfoot River 4 132% 97%Portneuf River 6 164% 114%

Snake ab Palisades Resv 33 133% 95%Willow Creek - Ririe 7 129% 108%

Greys River 4 137% 99%Salt River 5 132% 92%

Gros Ventre River 4 126% 91%Hoback River 6 155% 91%

Pacific Creek 4 147% 100%Buffalo Fork 3 139% 93%

Henrys Fork ab Rexburg 13 110% 100%Snake River ab Jackson Lake 12 123% 99%

Henrys Fork-Falls River 8 105% 102%Teton River 5 119% 97%

2810Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions




5710 2650APR-SEP 3090 4010 4640 165% 5270 6190

152 174 93Snake R at Neeley 2 APR-JUL 2960 3770 4330 163% 4890

MAR-SEP 101 122 137 147%

67Portneuf R at Topaz MAR-JUL 85 103 115 151% 126 144 76

6270 3780Willow Ck nr Ririe 2 MAR-JUL 68 95 117 175% 141 180

4960 5410 3240APR-SEP 4490 5020 5380 142% 5740

Snake R nr Heise 2 APR-JUL 3890 4340 4650 144%

3010APR-SEP 4150 4650 4990 143% 5330 5830 3500

735 370Snake R nr Irwin 2 APR-JUL 3610 4040 4330 144% 4620 5050

550 620 300APR-SEP 465 545 600 162% 655

Salt R ab Reservoir nr Etna APR-JUL 385 455 500 167%

305APR-SEP 425 480 515 143% 555 610 360

4140 2500Greys R ab Reservoir nr Alpine APR-JUL 365 410 445 146% 475 525

3340 3610 2170APR-SEP 3080 3400 3610 144% 3830

Snake R ab Reservoir nr Alpine 2 APR-JUL 2700 2970 3160 146%

280APR-SEP 345 395 430 134% 465 510 320

295 173Buffalo Fk ab Lava Ck nr Moran APR-JUL 310 350 380 136% 405 445

255 280 164APR-SEP 210 235 250 145% 270

Pacific Ck at Moran APR-JUL 199 225 240 146%

765APR-SEP 845 965 1040 123% 1130 1240 845

770 510Snake R nr Moran 2 APR-JUL 770 875 950 124% 1020 1120

635 700 465APR-SEP 525 595 645 126% 695

Snake R at Flagg Ranch APR-JUL 475 545 590 127%

1400APR-SEP 1490 1770 1970 110% 2160 2450 1790

690 435Henrys Fk nr Rexburg 2 APR-JUL 1190 1410 1560 111% 1710 1930

520 585 365APR-SEP 435 510 560 129% 615

Teton R nr St Anthony APR-JUL 370 435 475 130%

154APR-SEP 192 230 255 132% 280 315 193

600 435Teton R nr Driggs APR-JUL 155 185 205 133% 225 255

455 500 365APR-SEP 420 475 510 117% 545

Falls R nr Ashton 2 APR-JUL 345 390 425 116%

530APR-SEP 575 680 750 106% 820 920 710

10%(KAF)

30yr Avg(KAF)

Henrys Fk nr Ashton 2 APR-JUL 420 510 565 107% 625 710

Upper Snake River Basin Streamflow Forecasts - February 1, 2017Forecast Exceedance Probabilities for Risk Assessment



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

Southside Snake River Basins

February 1, 2017



Numerous storms pummeled the Southside Snake River basins during January. Monthly precipitation ranged from 150-200% of average, while water year to date precipitation ranges from 130-160% of average. Snowpacks range from 120-165% of median, with the greatest amounts in the Bruneau and Owyhee River basins. The Owyhee basin snowpack is now starting to exceed its seasonal peak snow water amounts that typically occur in mid-March.


Reservoir storage is much better than a year ago. Oakley Reservoir is currently 81% of average, 24% capacity, Salmon Falls is 100% of average, 24% of capacity, while Lake Owyhee is 71% of average, and 35% of capacity. Streamflow forecasts range from 150-220% of average for Salmon Falls, Bruneau River, and the Owyhee River forecast points. Forecasts for Goose Creek, Trapper Creek, and Oakley Reservoir inflow range from 115-130% of average. Irrigators and water sport recreationalists can expect plentiful runoff in 2017.

Brownlee Reservoir 1125.1 1094.8 1189.0 1420.0

Wild Horse Reservoir 33.1 11.1 33.2 71.5Lake Owyhee 246.8 98.1 345.3 715.0

Oakley Reservoir 18.3 13.8 22.5 75.6Salmon Falls Reservoir 43.3 18.6 43.3 182.6

Owyhee Basin Snotel Total 8 162% 154%



(KAF)Capacity

(KAF)

Reynolds Creek 7 146% 136%Owyhee Basin Total 11 163% 149%

Salmon Falls Creek 7 127% 153%Bruneau River 8 154% 153%

Raft River 2 161% 140%Goose-Trapper Creeks 2 123% 141%




27200 34400 22280Normals based on 1981-2010 reference period: streamflow, precipitation, & reservoir normals are averages, SWE normals are medians.1) 90% and 10% exceedance probabilities are actually 95% and 5%2) Forecasts are for unimpaired flows. Actual flow will be dependent on management of upstream reservoirs and diversions

APR-SEP 13500 20700 23900 107%

405Snake R bl Lower Granite Dam 1 APR-JUL 12000 18400 21300 107% 24200 30600 19848

1770 665APR-SEP 495 710 855 211% 1000 1210

1470 1720 635FEB-SEP 940 1190 1350 203% 1520

Owyhee R bl Owyhee Dam 2 FEB-JUL 905 1150 1310 206%

595APR-SEP 455 665 810 222% 955 1160 365

1620 580FEB-SEP 865 1100 1260 212% 1420 1660

55 68 22Owyhee R nr Rome FEB-JUL 845 1080 1230 212% 1390

APR-JUL 25 38 46 209%

28MAR-SEP 34 46 54 200% 61 73 27

16.1 8.8Owyhee R nr Gold Ck 2 MAR-JUL 36 47 55 196% 63 75

370 425 215Reynolds Ck at Tollgate MAR-JUL 7.1 9.8 11.6 132% 13.4

MAR-SEP 245 300 335 156%

85Bruneau R nr Hot Spring MAR-JUL 240 290 325 159% 360 410 205

168 81MAR-SEP 88 111 127 149% 144 172

46 57 31Salmon Falls Ck nr San Jacinto MAR-JUL 85 107 123 152% 140

MAR-SEP 23 32 38 123%

7.1Oakley Reservoir Inflow MAR-JUL 21 29 35 125% 42 53 28

9.1 5.9MAR-SEP 6.2 7.3 8.2 115% 9.1 10.5

36 47 24Trapper Ck nr Oakley MAR-JUL 5.1 6.2 6.9 117% 7.8

MAR-SEP 16.5 24 30 125%

30yr Avg(KAF)

Goose Ck abv Trapper Ck nr Oakley MAR-JUL 15.9 23 28 127% 34 44 22



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

10%(KAF)

Southside Snake River Basins Streamflow Forecasts - February 1, 2017

Bear River Basin February 1, 2017



More than anywhere in Idaho, the far southeastern corner of the state has been repeatedly hit by potent winter storms. The Wyoming Range to the west, and the Unita Mountains of Utah to the south have also been in the bullseye of storm tracks. December precipitation was 215-235% of average, bringing water year to date precipitation up to 160% of average for the Bear River above the Idaho-Utah border. Snowpack in the Bear River drainages ranges from 150-170% of median and are now about to exceed the peak seasonal snow water content that typically occurs in late March to early April.


Bear Lake is storing 79% of average, which is 35% of capacity. April-July streamflow forecasts range from 160-225% of average in the Bear River basin and its tributaries. There is enough water in Bear Lake to provide its water users with an adequate irrigation supply.

Bear Lake 459.2 472.2 584.8 1302.0Montpelier Reservoir 2.1 2.5 1.7 4.0

Malad River 1 172% 107%



(KAF)Capacity

(KAF)

Cub River 1 155% 101%Bear River ab ID-UT Line 18 162% 98%

Montpelier Creek 2 163% 87%Mink Creek 1 148% 86%

Smiths-Thomas Forks 4 159% 95%Bear River ab WY-ID Line 10 167% 104%





111Blacksmith Fk nr Hyrum APR-JUL 73 86 95 221% 104 117 43

114 45Logan R nr Logan APR-JUL 147 173 190 171% 205 235

525 615 205Little Bear at Paradise APR-JUL 62 77 88 196% 98

MAR-JUL 315 405 465 227%

215FEB-SEP 390 495 565 235% 635 735 240

197 104Bear R bl Stewart Dam 2 FEB-JUL 345 440 500 233% 560 655

152 169 89APR-SEP 128 149 162 156% 176

Smiths Fk nr Border APR-JUL 111 128 140 157%

128Big Ck nr Randolph APR-JUL 3.6 5.4 6.6 174% 7.8 9.6 3.8

290 121APR-SEP 114 171 210 164% 250 305

215 240 123Bear R ab Resv nr Woodruff APR-JUL 112 164 200 165% 235

APR-SEP 151 178 196 159%

30yr Avg(KAF)

Bear R nr UT-WY State Line APR-JUL 139 163 179 160% 195 220 112



90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

10%(KAF)

Bear River Basin Streamflow Forecasts - February 1, 2017

Streamflow Adjustment List for All Forecasts Published in Idaho Water Supply Outlook Report: Streamflow forecasts are projections of runoff volumes that would occur without influences from upstream reservoirs or diversions. These values are referred to as natural, unregulated or adjusted flows. To make these adjustments, changes in reservoir storage, diversions, and inter-basin transfers are added or subtracted from the observed (actual) streamflow volumes. The following list documents the adjustments made for each forecast point. (Revised Feb. 2015). Panhandle Region Kootenai R at Leonia, MT (2) + Lake Koocanusa storage change Moyie R at Eastport – no corrections Boundary Ck nr Porthill – no corrections Clark Fork R at Whitehorse Rapids (2) + Hungry Horse storage change + Flathead Lake storage change + Noxon Res storage change Pend Oreille Lake Inflow (2) + Pend Oreille R at Newport, WA + Hungry Horse Res storage change + Flathead Lake storage change + Noxon Res storage change + Lake Pend Oreille storage change + Priest Lake storage change Priest R nr Priest R (2) + Priest Lake storage change NF Coeur d' Alene R at Enaville - no corrections St. Joe R at Calder- no corrections Spokane R nr Post Falls (2) + Lake Coeur d' Alene storage change Spokane R at Long Lake, WA (2) + Lake Coeur d' Alene storage change + Long Lake, WA storage change Clearwater River Basin Selway R nr Lowell - no corrections Lochsa R nr Lowell - no corrections Dworshak Res Inflow (2) + Clearwater R nr Peck - Clearwater R at Orofino + Dworshak Res storage change Clearwater R at Orofino - no corrections Clearwater R at Spalding (2) + Dworshak Res storage change Salmon River Basin Salmon R at Salmon - no corrections Lemhi R nr Lemhi – no corrections MF Salmon R at MF Lodge – no corrections SF Salmon R nr Krassel Ranger Station – no corrections Johnson Creek at Yellow pine – no corrections Salmon R at White Bird - no corrections West Central Basins Boise R nr Twin Springs - no corrections SF Boise R at Anderson Ranch Dam (2) + Anderson Ranch Res storage change Mores Ck nr Arrowrock Dam – no corrections

Boise R nr Boise (2) + Anderson Ranch Res storage change + Arrowrock Res storage change + Lucky Peak Res storage change SF Payette R at Lowman - no corrections Deadwood Res Inflow (2) + Deadwood R bl Deadwood Res nr Lowman + Deadwood Res storage change Lake Fork Payette R nr McCall – no corrections NF Payette R at Cascade (2) + Payette Lake storage change + Cascade Res storage change NF Payette R nr Banks (2) + Payette Lake storage change + Cascade Res storage change Payette R nr Horseshoe Bend (2) + Deadwood Res storage change + Payette Lake storage change + Cascade Res storage change Weiser R nr Weiser - no corrections Wood and Lost Basins Little Lost R bl Wet Ck nr Howe - no corrections Big Lost R at Howell Ranch - no corrections Big Lost R bl Mackay Res nr Mackay (2) + Mackay Res storage change Little Wood R ab High Five Ck – no corrections Little Wood R nr Carey (2) + Little Wood Res storage change Big Wood R at Hailey - no corrections Big Wood R ab Magic Res (2) + Big Wood R nr Bellevue (1912-1996) + Big Wood R at Stanton Crossing nr Bellevue (1997 to present) + Willow Ck (1997 to present) Camas Ck nr Blaine – no corrections Magic Res Inflow (2) + Big Wood R bl Magic Dam + Magic Res storage change Upper Snake River Basin Falls R nr Ashton (2) + Grassy Lake storage change + Diversions from Falls R ab nr Ashton Henrys Fork nr Ashton (2) + Henrys Lake storage change + Island Park Res storage change Teton R nr Driggs - no corrections Teton R nr St. Anthony (2) - Cross Cut Canal into Teton R + Sum of Diversions for Teton R ab St. Anthony + Teton Dam for water year 1976 only

Henrys Fork nr Rexburg (2) + Henrys Lake storage change + Island Park Res storage change + Grassy Lake storage change + 3 Diversions from Falls R ab Ashton-Chester + 6 Diversions from Falls R abv Ashton + 7 Diversions from Henrys Fk btw Ashton to St. Anthony + 21 Diversions from Henrys Fk btw St. Anthony to Rexburg Snake R nr Flagg Ranch, WY – no corrections Snake R nr Moran, WY (2) + Jackson Lake storage change Pacific Ck at Moran, WY - no corrections Buffalo Fork ab Lava nr Moran, WY - no corrections Snake R ab Res nr Alpine, WY (2) + Jackson Lake storage change Greys R nr Alpine, WY - no corrections Salt R R nr Etna, WY - no corrections Palisades Res Inflow (2) + Snake R nr Irwin + Jackson Lake storage change + Palisades Res storage change Snake R nr Heise (2) + Jackson Lake storage change + Palisades Res storage change Ririe Res Inflow (2) + Willow Ck nr Ririe + Ririe Res storage change The forecasted natural volume for Willow Creek nr Ririe does not include Grays Lake water diverted from Willow Creek drainage through the Clarks Cut diversion and into Blackfoot Reservoir. Blackfoot R ab Res nr Henry (2) + Blackfoot Res storage change The forecasted Blackfoot Reservoir Inflow includes Grays Lake water diverted from the Willow Creek drainage through the Clarks Cut diversion and into Blackfoot Reservoir. Portneuf R at Topaz - no corrections American Falls Res Inflow (2) + Snake R at Neeley + Jackson Lake storage change + Palisades Res storage change + American Falls storage change + Teton Dam for water year 1976 only Southside Snake River Basins Goose Ck nr Oakley - no adjustments Trapper Ck nr Oakley - no adjustments Oakley Res Inflow - flow does not include Birch Creek + Goose Ck + Trapper Ck Salmon Falls Ck nr San Jacinto, NV - no corrections Bruneau R nr Hot Springs - no corrections Reynolds Ck at Tollgate - no corrections Owyhee R nr Gold Ck, NV (2) + Wildhorse Res storage change Owyhee R nr Rome, OR – no Corrections Owyhee Res Inflow (2)

+ Owyhee R bl Owyhee Dam, OR + Lake Owyhee storage change + Diversions to North and South Canals Bear River Basin Bear R nr UT-WY Stateline, UT- no corrections Bear R abv Res nr Woodruff, UT- no corrections Big Ck nr Randolph, UT - no corrections Smiths Fork nr Border, WY - no corrections Bear R bl Stewart Dam (2) + Bear R bl Stewart Dam + Rainbow Inlet Canal Little Bear R at Paradise, UT - no corrections Logan R nr Logan, UT - no corrections Blacksmith Fk nr Hyrum, UT - no corrections Reservoir Capacity Definitions (Units in 1,000 Acre-Feet, KAF) Different agencies use various definitions when reporting reservoir capacity and contents. Reservoir storage terms include dead, inactive, active, and surcharge storage. This table lists the volumes for each reservoir, and defines the storage volumes NRCS uses when reporting capacity and current reservoir storage. In most cases, NRCS reports usable storage which includes active and/or inactive storage. (Revised Feb. 2015) Basin- Lake or Dead Inactive Active Surcharge NRCS NRCS Capacity Reservoir Storage Storage Storage Storage Capacity Includes Panhandle Region Hungry Horse 39.73 --- 3451.00 --- 3451.0 Active Flathead Lake Unknown --- 1791.00 --- 1791.0 Active Noxon Unknown --- 335.00 --- 335.0 Active Lake Pend Oreille 406.20 112.40 1042.70 --- 1561.3 Dead + Inactive + Active Lake Coeur d'Alene Unknown 13.50 225.00 --- 238.5 Inactive + Active Priest Lake 20.00 28.00 71.30 --- 119.3 Dead + Inactive + Active Clearwater Basin Dworshak Unknown 1452.00 2016.00 --- 3468.0 Inactive + Active West Central Basins Anderson Ranch 24.90 37.00 413.10 --- 450.1 Inactive + Active Arrowrock Unknown --- 272.20 --- 272.2 Active Lucky Peak Unknown 28.80 264.40 13.80 293.2 Inactive + Active Lake Lowell 7.90 5.80 159.40 --- 165.2 Inactive + Active Deadwood Unknown --- 161.90 --- 161.9 Active Cascade Unknown 46.70 646.50 --- 693.2 Inactive + Active Mann Creek 1.61 0.24 11.10 --- 11.1 Active Wood and Lost Basins Mackay 0.13 --- 44.37 --- 44.4 Active Little Wood Unknown --- 30.00 --- 30.0 Active Magic Unknown --- 191.50 --- 191.5 Active Upper Snake Basin Jackson Lake Unknown --- 847.00 --- 847.0 Active Palisades 44.10 155.50 1200.00 --- 1400.0 Dead + Inactive+Active Henrys Lake Unknown --- 90.40 --- 90.4 Active Island Park 0.40 --- 127.30 7.90 135.2 Active + Surcharge Grassy Lake Unknown --- 15.18 --- 15.2 Active Ririe 4.00 6.00 80.54 10.00 80.5 Active Blackfoot 0.00 --- 333.50 3.50 333.50 Active (rev. 2/1/2015) American Falls Unknown --- 1672.60 --- 1672.6 Active Southside Snake Basins Oakley 0.00 --- 75.60 --- 75.6 Active Salmon Falls 48.00 5.00 182.65 --- 182.6 Active Wild Horse Unknown --- 71.50 --- 71.5 Active Lake Owyhee 406.83 --- 715.00 --- 715.0 Active Brownlee 0.45 444.70 975.30 --- 1420.0 Inactive + Active Bear River Basin Bear Lake 5000.00 119.00 1302.00 --- 1302.0 Active: Capacity does not include 119 KAF that can be used, historic values below this level are rounded to zero Montpelier 0.21 --- 3.84 --- 4.0 Dead + Active

Interpreting Water Supply Forecasts

Each month, five forecasts are issued for each 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 if they are to use the information correctly when making operational decisions. The following is an explanation of each of the forecasts. 90 Percent Chance of Exceedance Forecast. There is a 90 percent chance that the actual streamflow volume will exceed this forecast value, and there is a 10 percent chance that the actual streamflow volume will be less than this forecast value. 70 Percent Chance of Exceedance Forecast. There is a 70 percent chance that the actual streamflow volume will exceed this forecast value, and there is a 30 percent chance that the actual streamflow volume will be less than this forecast value. 50 Percent Chance of Exceedance Forecast. There is a 50 percent chance that the actual streamflow volume will exceed this forecast value, and there is a 50 percent chance that the actual streamflow volume will be less than this forecast value. Generally, this forecast is the middle of the range of possible streamflow volumes that can be produced given current conditions. 30 Percent Chance of Exceedance Forecast. There is a 30 percent chance that the actual streamflow volume will exceed this forecast value, and there is a 70 percent chance that the actual streamflow volume will be less than this forecast value. 10 Percent Chance of Exceedance Forecast. There is a 10 percent chance that the actual streamflow volume will exceed this forecast value, and there is a 90 percent chance that the actual streamflow volume will be less than this forecast value.

*Note: There is still a 20 percent chance that actual streamflow volumes will fall either below the 90 percent exceedance forecast or above the 10 percent exceedance forecast.

These forecasts represent the uncertainty inherent in making streamflow predictions. This uncertainty may include sources such as: unknown future weather conditions, uncertainties associated with the various prediction methodologies, and the spatial coverage of the data network in a given basin.

30-Year Average. The 30-year average streamflow for each forecast period is provided for comparison. The average is based on data from 1981-2010. The % AVG. column compares the 50% chance of exceedance forecast to the 30-year average streamflow; values above 100% denote when the 50% chance of exceedance forecast would be greater than the 30-year average streamflow. AF - Acre-feet, forecasted volume of water are typically in thousands of acre-feet (KAF). These forecasts are given to users to help make risk-based decisions. Users can select the forecast corresponding to the level of risk they are willing to accept in order to minimize the negative impacts of having more or less water than planned for. To Decrease the Chance of Having Less Water than Planned for A user might determine that making decisions based on a 50 percent chance of exceedance forecast is too much risk to take (there is still a 50% chance that the user will receive less than this amount). To reduce the risk of having less water than planned for, users can base their operational decisions on one of the forecasts with a greater chance of being exceeded such as the 90 or 70 percent exceedance forecasts. To Decrease the Chance of Having More Water than Planned for A user might determine that making decisions based on a 50 percent chance of exceedance forecast is too much risk to take (there is still a 50% chance that the user will receive more than this amount). To reduce the risk of having more water than planned for, users can base their operational decisions on one of the forecasts with a lesser chance of being exceeded such as the 30 or 10 percent exceedance forecasts. Forecast use example: Using the 50 Percent Exceedance Forecast. Using the example forecasts shown on the next page, there is a 50% chance that actual streamflow volume at the Henry’s Fork near Ashton will be less than 280 KAF between June 1 and Sept. 30. There is also a 50% chance that actual streamflow volume will be greater than 280 KAF. Using the 90 and 70 Percent Exceedance Forecasts. If an unexpected shortage of water could cause problems (such as irrigated agriculture), users might want to plan on receiving 245 KAF during Jun 1 through September 30 (from the 70 percent exceedance forecast). There is a 30% chance of receiving less than 245 KAF.

Alternatively, if users determine the risk of using the 70 percent exceedance forecast is too great, then they might plan on receiving 198 KAF (from the 90 percent exceedance forecast). There is 10% chance of receiving less than 72 KAF. Using the 30 or 10 Percent Exceedance Forecasts. If an unexpected excess of water could cause problems (such as operating a flood control reservoir), users might plan on receiving 315 KAF between June 1 and

Sept. 30 (from the 30 percent exceedance forecast). There is a 30% chance of receiving more than 315 KAF. Alternatively, if users determine the risk of using the 30 percent exceedance forecast is too great, then they might plan on receiving 360 KAF (from the 10 percent exceedance forecast). There is a 10% chance of receiving more than 360 KAF. Users could also choose a volume in between any of these values to reflect their desired risk level.

Interpreting Snowpack Plots

Basin snowpack plots represent snow water equivalent indices using the average daily SNOTEL data1 from several sites in or near individual basins. The solid red line (2015), which represents the current water year snowpack water content, can be compared to the normal dashed black line (Median) which is considered “normal”, as well as the SNOTEL observed historical snowpack range for each basin. This allows users to gather important information about the current year’s snowpack as well as the historical variability of snowpack in each basin. The gray shaded area represents the interquartile range (also known as the “middle fifty”), which is the 25th to 75th percentiles of the historical daily snowpack data for each basin. Percentiles depict the value of the average snowpack below which the given percent of historical years fall. For example, the top part of the interquartile range (75th percentile) indicates that the snowpack index has been below this line for 75 percent of the period of record, whereas the reverse is true for the lower part of the interquartile range (25th percentile). This means 50 percent of the time the snowpack index is within the interquartile range (gray area) during the period of record. 1 All data used for these plots come from daily SNOTEL data only and does not include snow course data (collected monthly), whereas the official basin snowpack percent of normal includes both SNOTEL and snow course data, potentially leading to slight discrepancies between plots and official basin percent of normal.

Upper Snake River Basin Streamflow Forecasts - June 1, 2015

Forecast Period

Forecast Exceedance Probabilities for Risk Assessment

30yr Avg(KAF)

<---Drier----------------Projected Volume-------------Wetter--->

Forecast Point 90%(KAF)

70%(KAF)

50%(KAF) % Avg

30%(KAF)

10%(KAF)

Henrys Fk nr Ashton JUN-JUL 72 106 129 56 152 186 230JUN-SEP 198 245 280 68 315 360 410

USDA Natural Resources Conservation Service 9173 West Barnes Drive, Suite C Boise ID 83709-1574

OFFICIAL BUSINESS

Issued by Leonard Jordan, Acting Chief Natural Resources Conservation Service Washington, DC Released by Curtis Elke, State Conservationist Shawn Nield, State Soil Scientist Natural Resources Conservation Service Boise, Idaho Prepared by Idaho Snow Survey Staff Ron Abramovich, Water Supply Specialist Danny Tappa, Hydrologist John Wilford, Electronics Technician Forecasts and Assistance provided by Rashawn Tama, Forecast Hydrologist Jolyne Lea, Forecast Hydrologist NRCS, National Water and Climate Center, Portland, Oregon Numerous other groups and agencies provide funding and/or cooperative support for the collection, operation and maintenance of the Cooperative Idaho Snow Survey Program. Your cooperation is greatly appreciated.

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