Colorado Water Supply Outlook Report April 1, 2020 Much like February, precipitation in March maintained normal to above normal snowpack in the Front Range. The Loveland Pass area, seen in the photo above, was no exception. Both the Loveland and the Grizzly Peak SNOTEL measured 99 and 109 percent of normal snow water equivalent for the end of March. Photo By: Joel Atwood Date: March 21st, 2020 NOTICE: Due to the COVID-19 outbreak most end-of-month snow surveys were not conducted and are not included as part of the April 1st water supply report. REMINDER: We are soliciting field work photos from the field again this year. Each month we will pick one to grace the cover of this report! Please include information on where, when and of who/what the photo was taken. Contents Colorado Statewide Water Supply Conditions........................................................................................................................ 3 Summary ............................................................................................................................................................................. 3 Snowpack ............................................................................................................................................................................ 3 Precipitation ........................................................................................................................................................................ 4 Reservoir Storage ................................................................................................................................................................ 5 Streamflow .......................................................................................................................................................................... 6 GUNNISON RIVER BASIN ......................................................................................................................................................... 7 UPPER COLORADO RIVER BASIN ........................................................................................................................................... 12 SOUTH PLATTE RIVER BASIN ................................................................................................................................................. 16 YAMPA, WHITE, NORTH PLATTE, AND LARAMIE RIVER BASINS ........................................................................................... 21 ARKANSAS RIVER BASIN ........................................................................................................................................................ 25 UPPER RIO GRANDE RIVER BASIN ......................................................................................................................................... 29 SAN MIGUEL, DOLORES, ANIMAS, AND SAN JUAN RIVER BASINS ........................................................................................ 34 How to Read Snowpack Graphs ............................................................................................................................................ 38 How Forecasts Are Made ...................................................................................................................................................... 39 Interpreting the Forecast Graphics ....................................................................................................................................... 40 The U.S. Department of Agriculture (USDA) prohibits discrimination against its customers. 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Persons with disabilities who require alternative means for communication of program information (e.g., Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720‐2600 (voice and TDD). 2 Colorado Statewide Water Supply Conditions Summary Colorado Statewide Time Series Snowpack Summary 25 Snow Water Equivalent (inches) 20 Based on Provisional SNOTEL data as of Apr 06, 2020 Current as Pct of Normal: 102% Current as Pct of Avg: 100% Current as Pct of Last Year: 77% Current as Pct of Peak: 102% Normal as Pct of Peak: 100% Pct of Normal Needed to Reach Peak: Current SWE Equals or Exceeds Avg Peak Normal Peak Date: Apr 07 15 10 5 0 Oct 01 Nov 01 Dec 01 Median Jan 01 Feb 01 Mar 01 WY2017 WY2018 Apr 01 May 01 WY2019 Jun 01 Jul 01 Average Aug 01 Sep 01 WY2020 Current snowpack conditions across Colorado are generally near normal. Conditions range from a low of 97 percent of normal in the Gunnison River Basin to a high of 117 percent of normal in the South Platte River Basin. With peak snowpack commonly occurring in early to mid-April, this provides a good metric to base an idea on what this year’s snowmelt runoff may be. That said, with a dry late summer and fall, streamflow forecasts have been trending lower than the snowpack values, with respect to normal. Many factors contribute to this but a large portion of that is due to drier than usual soils which will absorb future snowmelt and precipitation on its way to stream channels. Streamflow forecasts are for generally above normal values in Northern Colorado and below normal in the southern half of the state. Statewide reservoir storage is currently 107 percent of average and while this varies basin to basin near-normal conditions in most areas should provide some flexibility in operations to benefit overall water resources for the state and downstream as well. Now that we are near peak snowpack accumulation future weather will largely dictate how flat or steep the curve of the hydrograph of rivers across the state will be over the coming months. 3 Snowpack Early this month, several storms moved across the state improving a below-normal snowpack in southwestern Colorado. Both the Gunnison and combined San Miguel, Dolores, Animas river basins ended March with nearnormal snow water equivalent (SWE) at 97 and 99 percent of normal, respectively. The Upper Rio Grande River Basin also ended the month with 100 percent of median SWE. Despite improvements in these basins, the snowpack is generally sporadic, ranging from Medano Pass and Upper Rio Grande SNOTEL site which recorded 271 and 196 percent of normal compared to Lone Cone and Chamita with 77 percent of normal SWE. In the combined San Miguel, Dolores, Animas river basins 38 percent of SNOTEL sites recorded below normal SWE. In the Gunnison and Upper Rio Grande river basins 78 and 45 percent of SNOTEL sites recorded below normal SWE. In the Upper Rio Grande River Basin snowpack is generally near normal in the north and below normal in the south. In the Gunnison River Basin snowpack is particularly low on the Grand Mesa. Northern river basins in Colorado maintained substantial above-normal SWE driving the snowpack statewide to 107 percent of median. The Colorado, South Platte and combined Yampa, White and North Platte river basins ended the month with 113, 117, and 111 percent of median SWE, respectively. Despite the above-normal snowpack in much of northern Colorado, SNOTEL sites in southwestern Flattops and the Grand Mesa ended the month below-normal. The far southeastern mountains have also recorded below normal snowpack. The Apishapa, Whiskey Creek and Ute Creek SNOTEL sites on the eastern slopes of the southern Sangre de Cristo Mountains recorded 43 and 96, and 80 percent of median SWE. Despite these deficits, the Arkansas River Basin ended the month with 105 percent of normal, largely due to above-normal snowpack in the Upper Arkansas River Basin. 4 Precipitation Overall, precipitation amounts for the month of March were below average for most of the state, with statewide water year-to-date precipitation currently at 91 percent of average. Drought conditions remain in place for much of the central and southern portions of the state and have slightly deteriorated in southcentral Colorado. Several moisture-rich systems moved across the southwest portions of the state which brought some much-needed relief from the dry conditions that have persisted in those areas throughout much of the water year. The southern basins on the west side of the Continental Divide received higher amounts of precipitation than the southern basins on the east side, likely due to a rain-shadow effect as most of the systems came from the west. The combined San Miguel-Dolores-Animas-San Juan basins and Gunnison basin received 114 and 97 percent of average precipitation, respectively, bringing water year-to-date precipitation to 80 and 82 percent of average. On the east side of the divide, the Upper Rio Grande and Arkansas basins received 80 and 62 percent of average precipitation, respectively, bringing water year-to-date precipitation to 76 and 85 percent of average for those basins. In general, the northern and central mountains across the state received below average precipitation for the month of March. However, most of these basins are still near average for water year-to-date precipitation. The combined Yampa-White-North Platte river basins received 84 percent of average precipitation which brings water year-to-date precipitation to 100 percent of average. The Upper Colorado basin received 79 percent of average precipitation bringing water year-to date precipitation to 95 percent of average. Finally, the South Platte river basin received 83 percent of average precipitation bringing the water year-to-date to 107 percent of average. 5 Reservoir Storage Colorado Reservoir Storage Oct-19 Apr-20 Nov-19 May-20 Dec-19 Jun-20 Jan-20 Jul-20 Feb-20 Aug-20 Mar-20 Sep-20 140% Percent of Average Useable Storage 120% 100% 80% 60% 40% 20% 0% Gunnison Colorado South Platte Yampa, White & North Platte Arkansas Upper Rio Grande San Miguel, Dolores, Animas & San Juan Statewide Reservoir storage has continued to remain slightly above average with statewide storage totals currently at 107 percent of average. Most reservoirs across the state saw little to no change in storage levels for the month of March. This same time last year, statewide reservoir storage was 84 percent of average. Statewide reservoir storage is also currently 61 percent of capacity which could prove to be beneficial if the snowmeltrunoff season is above average or if flood conditions appear. All major basins across the state are above average for reservoir storage, except for the Rio Grande and Arkansas River basins, which currently are at 83 and 92 percent of average, respectively. The combined Yampa, White, and North Platte River basins are currently at 125 percent of average, slightly up from 123 percent at the beginning of March. The combined San Miguel, Dolores, Animas, and San Juan River basins are currently at 104 percent of average, slightly down from 107 percent of average at the beginning of March. The Gunnison and Upper Colorado River basins showed slight gains compared to last month and are currently at 111 and 115 percent of average, respectively. The South Platte River basin showed slight declines in reservoir storage for the month and is currently at 110 percent of average. In general, all the major basins across Colorado are near normal for reservoir storage. This should give reservoir operators flexibility with decision making once snowmelt runoff begins. 6 Streamflow Despite improvements to the overall water supply during March, southwestern Colorado is still expecting below-average streamflow volumes. On average the Gunnison, Upper Rio Grande and combined San Miguel, Dolores, Animas, and San Juan basins are forecasted to have 71, 69, and 68 percent of average runoff volumes. Early seasons precipitation deficits and below normal snowpack has reduced the amount of water available as runoff in these basins. In the Upper Rio Grande River Basin, 7 out of 15 forecast points have forecasted runoff volumes less than 70 percent of average. For the combined San Miguel, Dolores, Animas and San Juan basins, 8 out of 16 forecast points have forecasted runoff volumes less than 70 percent of average. In contrast to basins further west, the Arkansas River Basin is expecting near-average runoff volumes at 96 percent of normal. In general, forecast points in the southeastern part of the Arkansas basin are expecting below normal runoff whereas the upper basin is expecting above-average runoff. Despite receiving below average precipitation for March, northern Colorado basins, having accumulated substantial snowpack, are expecting above-average runoff volumes at most locations. The North Platte, South Platte, the combined Yampa and White River, and Upper Colorado basins have forecasted average streamflow runoff of 118, 104, 104, 100 percent of average, respectively. In total, 73 percent of all forecast points in these basins are expecting above-average runoff volumes. With most basins reaching peak snowpack conditions, certainty in the forecasts have increased. While it is still possible for late-season storms to deliver much-needed precipitation to southwestern Colorado, it is becoming increasingly likely that below-normal streamflow runoff will occur in these basins. 7 GUNNISON RIVER BASIN April 1, 2020 Snowpack in the Gunnison River basin is slightly below normal at 97% of the median. Precipitation for March was 97% of average which brings water year-to-date precipitation to 82% of average. Reservoir storage at the end of March was 111% of average compared to 67% last year. Current streamflow forecasts range from 54% of average for Surface Creek at Cedaredge to 93% for Cochetopa Creek below Rock Creek near Parlin. Gunnison River Basin Mountain Snowpack Snow Water Equivalent (Inches) 30 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 140 120 Percent of Average 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date Apr May 8 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Upper Gunnison Surface Creek Uncompahgre Basin-Wide Total # of Sites 10 2 3 13 % Median 97 78 98 97 Last Year % Median 148 142 152 149 *SWE values calculated using first of month SNOTEL data and snow course measurements End of March Reservoir Storage Percent Average 350% Percent Capacity 300% 250% 200% 150% 100% 50% 0% Reservoir Storage End of March 2020 Reservoir BLUE MESA RESERVOIR CRAWFORD RESERVOIR CRYSTAL RESERVOIR FRUITGROWERS RESERVOIR FRUITLAND RESERVOIR MORROW POINT RESERVOIR PAONIA RESERVOIR RIDGWAY RESERVOIR SILVERJACK RESERVOIR TAYLOR PARK RESERVOIR VOUGA RESERVOIR BASINWIDE Number of Reservoirs Current Last Year Average Capacity (KAF) (KAF) (KAF) (KAF) 534.4 249.7 454.9 830.0 9.2 3.4 9.7 14.0 9.7 9.2 8.5 17.5 3.6 3.2 4.0 3.6 1.4 0.5 2.3 9.2 105.9 106.7 111.7 121.0 7.6 3.8 2.6 15.4 67.0 50.0 70.0 83.0 1.0 1.3 6.0 12.8 71.4 60.4 62.4 106.0 0.2 0.9 811.1 488.4 732.1 1213.4 10 11 10 11 10 GUNNISON RIVER BASIN Water Supply Forecasts April 1, 2020 Forecast Exceedance Probabilities Forecast Forecast Drier Future Conditions Wetter P000 Period Labels on chart represent volumes of water expressed in thousand acre?feet. 65 77 86 96 111 Taylor bl Apr?Jul Taylor Park 99 Reservoir 5U 57 62 6? 75 SIateRnr Apr?Jul I Crested Butte 33 102 118 130 142 162 EastRatAlmont Apr-Jul I 182 199 240 270 300 350 Gunnison Apr-Jul I Near Gunnison 370 17 23 28 33 42 Tomichi Ck at Apr-Jul I Sargents 30 6.6 11 14 18 24 Cochetopa Ck bl Apr?Jul I Rock Ck nr 1'5 Par"? 30 4s 63 80 109 Tomichi Ck at Apr?Jul I Gunnison 74 71 86 98 110 130 Lake Fk at Apr-Jul I Gateview 123 365 44-5 500 560 655 Gunnison at Apr-Jul I Blue Mesa Dem 675 35 4B 58 69 87 Muddy Ck bl Apr-Jul I Paonia 97 Reservoir 34 46 55 65 81 Apr-Jun I 91 37 49 58 68 84- Mar-Jun GunnisonR Apr-Jul I 9 hr Somerset 2 6.7 8 9.1 10 12 SurfaceCkat Apr?Jul i Cedaredge 17 56 69 79 90 107 Uncompahgre Apr?Jul I bl Ridgway 101? Resemir 58 79 95 113 141 Uncompahgre Apr-Jul I at Colona 1?37 695 870 1,000 1,140 1,360 Gunnison nr Apr-Jul I Grand Junction L480 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150% 160% Percent of Average (30 Yr Period) Legend 95Exceedance Exceeda nce Exceedance Exceedance Exceeds nce There Is 959619011: chance that There is a chance that There is a 50% chance that There Is a 30% chance that There is a 10%r'5% chance that flows will exceed this volume flows will exceed this volume ?ows will exceed this volume ?ows will exceed this volume flows exceed this volume When selected. the following historic stream?ow values and statistics will be shown. Period of Record Minimum 1981?2010 Normal Observed Stream?ow KAF Period of Record Maximum Streamfl'ow KAF (Veer) Stream?ow KAF Stream?ow KAF (Year) Some forecasts may be for volumes that are regulated or infiuenced by diversions and water management. UPPER COLORADO RIVER BASIN April 1, 2020 Snowpack in the Colorado River basin is above normal at 113% of the median. Precipitation for March was 79% of average which brings water year-to-date precipitation to 95% of average. Reservoir storage at the end of March was 115% of average compared to 90% last year. Current streamflow forecasts range from 85% of average for the Roaring Fork at Glenwood Springs to 113% for Green Mountain Reservoir Inflow. Colorado River Basin Mountain Snowpack Snow Water Equivalent (Inches) 30 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 160 140 Percent of Average 120 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date April May 12 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Blue River Upper Colorado Muddy Creek Eagle River Plateau Creek Roaring Fork Williams Fork Willow Creek Basin-Wide Total # of Sites Last Year % % Median Median 5 115 137 25 116 121 3 133 130 4 100 119 5 83 136 8 112 147 5 112 114 2 121 132 35 113 129 *SWE values calculated using first of month SNOTEL data and snow course measurements 13 End of March Reservoir Storage Percent Average 180% Percent Capacity 160% 140% 120% 100% 80% 60% 40% 20% 0% DILLON RESERVOIR LAKE GRANBY GREEN HOMESTAKE WILLOW WOLFORD SHADOW BASINWIDE RUEDI VEGA WILLIAMS MOUNTAIN RESERVOIR RESERVOIR RESERVOIR FORK CREEK MOUNTAIN MOUNTAIN RESERVOIR RESERVOIR RESERVOIR RESERVOIR RESERVOIR Reservoir Storage End of March 2020 Current Last Year Average Capacity Reservoir (KAF) (KAF) (KAF) (KAF) DILLON RESERVOIR 223.1 174.1 210.7 249.1 LAKE GRANBY 323.8 270.1 265.0 465.6 GREEN MOUNTAIN RESERVOIR 62.4 42.6 61.2 146.8 HOMESTAKE RESERVOIR 41.2 18.6 26.1 43.0 RUEDI RESERVOIR 68.3 55.8 63.2 102.0 VEGA RESERVOIR 15.2 7.0 14.0 32.9 WILLIAMS FORK RESERVOIR 74.4 64.2 60.8 97.0 WILLOW CREEK RESERVOIR 8.1 7.5 7.2 9.1 WOLFORD MOUNTAIN RESERVOIR 50.9 33.5 43.7 65.9 SHADOW MOUNTAIN RESERVOIR 17.2 17.3 17.3 18.4 BASINWIDE 884.6 690.7 769.2 1229.8 Number of Reservoirs 10 10 10 10 14 UPPER COLORADO RIVER BASIN Water Supply Forecasts April 1, 2020 Forecast Exceedance Probabilities Forecast Forecast Drier Future Conditions Wetter POW Period Labels on chart represent volumes of water expressed in thousand acre-feet. 174 205 230 255 295 Colorado bl Apr-Jul I I Lake Granby 220 29 40 48 57 71 Willow Ck bl Apr-Jul I Willow Ck 47 74 87 97 107 124 Williams Fk bl Apr-Jul Williams Fk 97 Resem" 42 53 61 70 83 Muddy Creek bl Apr-Jul I I Wolford 54 Resewo'r 141 166 185 205 235 Blue bl Dillon Apr-Jul I I Reservoir 163 240 280 310 340 385 Blue bl Green Apr-Jul I I Mountain 275 Resewo'r 255 305 340 330 440 Eagle bl Apr-Jul I Gypsum 335 1,100 1,320 1,480 1,650 1,920 Colorado nr Apr-Jul I Dotsero 1,400 108 125 137 150 171 Frying Pan at Apr-Jul I Ruedi 139 445 525 585 645 740 Roaring Fk at Apr-Jul Glenwood 690 8'3??93 1,700 2,000 2,230 2,460 2,820 Colorado nr Apr-Jul I Cameo 2,350 I I I I I 60% 70% 80% 90% 100% 110% 120% 130% 140% 150% 160% Percent of Average (30 Yr Period) Legend 95Exceedance Exceedance Exceedance Exceedance Exceedance I There is a 95%1?90% chance that flows will exceed this volume There is a 50% chance that There is a 30% chance that There is a chance that flows will exceed this volume flows will exceed this volume ?ows wilt exceed this volume There is a chance that flows will exceed this volume Period of Record Minimum Stream?ow KAF (Year) When selected, the following historic stream?ow values and statistics will be shown. Period of Record Maximum Stream?ow KAF (Year) 1981-2010 Normal Stream?ow KAF Observed Stream?ow KAF Some forecasts may be for volumes that are regulated or in?uenced by diversions and water management. 15 SOUTH PLATTE RIVER BASIN April 1, 2020 Snowpack in the South Platte River basin is above normal at 117% of the median. Precipitation for March was 83% of average which brings water year-to-date precipitation to 107%. Reservoir storage at the end of March was 110% of average compared to 102% last year. Current streamflow forecasts range from 74% of average for Bear Creek above Evergreen to 121% for the South Platte at Antero Reservoir Inflow. South Platte River Basin Mountain Snowpack Snow Water Equivalent (Inches) 30 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 200 180 Percent of Average 160 140 120 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date Apr May 16 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Big Thompson Boulder Creek Cache La Poudre Clear Creek Saint Vrain Upper South Platte Basin-Wide Total Last Year % # of Sites % Median Median 3 118 110 5 121 109 2 113 119 2 109 112 1 143 429 6 117 138 19 117 120 *SWE values calculated using first of month SNOTEL data and snow course measurements 17 End of March Reservoir Storage Percent Average 180% Percent Capacity 160% 140% 120% 100% 80% 60% 40% 20% 0% Reservoir Storage End of March 2020 Reservoir ANTERO RESERVOIR BARR LAKE BLACK HOLLOW RESERVOIR BOYD LAKE CACHE LA POUDRE CARTER LAKE CHAMBERS LAKE CHEESMAN LAKE COBB LAKE ELEVENMILE CANYON RESERVOIR EMPIRE RESERVOIR FOSSIL CREEK RESERVOIR GROSS RESERVOIR HALLIGAN RESERVOIR HORSECREEK RESERVOIR HORSETOOTH RESERVOIR JACKSON LAKE RESERVOIR JULESBURG RESERVOIR LAKE LOVELAND RESERVOIR LONE TREE RESERVOIR MARIANO RESERVOIR MARSHALL RESERVOIR MARSTON RESERVOIR MILTON RESERVOIR POINT OF ROCKS RESERVOIR PREWITT RESERVOIR RIVERSIDE RESERVOIR SPINNEY MOUNTAIN RESERVOIR STANDLEY RESERVOIR TERRY RESERVOIR UNION RESERVOIR WINDSOR RESERVOIR BASINWIDE Number of Reservoirs Current (KAF) 20.0 29.0 3.6 35.4 9.9 106.1 4.2 54.7 18.1 100.1 32.6 9.3 14.4 5.4 11.5 144.0 26.0 20.7 2.9 7.1 0.2 7.0 6.4 21.0 70.7 24.6 55.0 37.0 38.9 5.5 10.5 10.5 942.3 32 Last Year (KAF) 19.6 28.8 4.0 31.4 10.6 105.2 2.1 62.7 15.9 99.3 32.8 10.0 7.2 6.4 8.8 95.6 26.1 17.4 0.0 7.1 4.0 6.8 7.4 21.7 69.3 22.3 55.8 33.8 29.0 5.5 10.5 8.7 865.8 32 Average (KAF) 14.9 27.8 2.8 28.7 8.1 94.9 3.2 65.1 11.6 96.4 31.2 8.0 10.4 4.1 12.7 113.7 26.9 19.4 6.8 7.4 3.6 6.6 6.7 19.1 64.4 21.4 53.1 28.2 36.2 4.8 10.6 9.7 858.5 32 Capacity (KAF) 19.9 30.1 6.5 48.4 10.1 108.9 8.8 79.0 22.3 98.0 36.5 11.1 29.8 6.4 14.7 149.7 26.1 20.5 10.3 8.7 5.4 10.0 13.0 23.5 70.6 28.2 55.8 49.0 42.0 8.0 13.0 15.2 1079.5 32 18 EIGHTH PLATTE RIVER BASIN Water Supply Furs-casts April 1. 1020 Farecast Exceeda nae Fruba bi1itie3 Forecast Fnracasl -: - - - - - - ErieFulure Cnndilims Weller :v Paint Pariud Lab-215 on chad represent val-4mm. 91' water exwesaed in thnusand weak-at 12 15 15 20 23 Scum Platte F: bl prul I I Antero 15 14 15 21 24 25 Apr-Sap S?ulh Platter F1 Apmul I I ab SplinnayI Res 13 50 51 5?5 55 Apr?Sap I 51 411 51 65 55 1'5 Scum Pietra Ft nr Apmm '1 Lake Gauge 50 50 52 T1 50 92 Apr-Sap w? 5-: 1'0 90 104 115 1515 51:1th Platte: Apmm Chaeaman LP: 10:1 5? 113 130 14-? In Apr-Sap I 125 9? 140 150 195 240 51:1th Platte a at Apr-Jul 1 South Platte 130 123 115 210 245 295 Apr-Sap I 225 4.5 5.1 12 15 15' Bear BI: ah Apr-Jul I Evergreen 15 5.4 12 15 1Q 25 Apr-Sap 20% 30% 40% 50% 50% 20% 00% 00% 100% 110% 120% 130% 140% 150% 150% Parmnt of?veraga {30 Period} Legend 353Ema-adama- Emeedanue Erase-dance Exceedanne Exmedanue There I: a 9mm 1M: Thur-.- a 70% mm Una! Theta a a 50% chum-e IMI Til-mu 30% Hun-In um Trove-5 a 1055-551 mum: 11w. Hun-5 Mlle-mud 1h: Irdurnc Haws-Nil claimed Ihr: vulurn-u 6151.de h: wiI 1h: vd?un.? Hams-I'll canned H115 huh-Th: Whan salaclawd. the fullnwing histmic strata m?u-w values and Etalislima wiIl be shun-m- Penna of Record Mmmum 1931-2010 Manna: Observed Srmamrmw IMF Penna 5.1 Recarn' Maximum Stream?crw RAF (?read Simam?ow KAF Stream?ow KAF (Year) Same Internals mayI 531m unrumas that are regulated at In?uenmd by diverslans and waler management. SOUTH PLATTE RIVER BASIN Water Supply Furs-casts April 1, man Farecast Exceada nae Fraba bililies Forecast Faracasl -: - - - - - - ErieFulure Candilims Weller :v P'Uil'll Pariud on wall represent valumea af water in lhnusand Bare-leer 5-4 100 111 122 133 Claar Ck al Apr-Jul I Guidan 105 94 132 14? 1TH Apr-Sap I 123 64 T9 39 99 11-4 Br. Vrain Cl: at Apr-Jul I Lyana 33 F3 92 1114 115 135 Apr-Sap Bouldar Bk nr Apr-Jul I Clrudall South Bauldar Apr-Jul I CH nr Eldorada 39 Springs: 31 39 4d 49 5? Apr-Sap I 43 55 32 10? 121 Thampaon ~3qu I at Canyon Maulh 9?0 1'3 95 11B 125 1d? Apr-Sap I 10? 15-4 210 245 230 325 Cache La Apr-Jul I PaudrB al 225 Canyon 153 225 26!: 295 350 Apr-Sap I 250 20% 36% 46% Ed?l? Rial ?d?l-h 9.1% lobe-B 115m 125m 13% while. ?lm 160% Paraant quvaraga {30 Yr Period] Legend 3517Exceadance Emeadanae Enceadanna Emaadanne 2* Thaw la a There a a mammal Them a 50% chance Lhal Than! :1 a 3m: manta Tram-n. a chants-Mn?: flu-w: mllmaccud ll'n Mum:- named lhra vulurn-u Mullcm ?151101le Haw: ml amend lhl: um Haws-w? Damn-d Hurrah-m Fla-nod of Record Mlmmum When Balaclad. the following histmic strata m?aw values and ataliatimB will be shun-m- 1931-3910 Narmal Observed Srream?aw HAF Pal-Tad 01? Return Maxlmum Stream?ow RAF Head SIrBarm'row KAF Slraam?ow KAF Wear) Emma (macasls mallI be fat mlurnaa that am: regulated Crl' Inlluanaad by divaralans and walar management. 20 YAMPA, WHITE, NORTH PLATTE, AND LARAMIE RIVER BASINS April 1, 2020 Snowpack in the Yampa, White & North Platte basins is above normal at 111% of the median. Precipitation for March was 84% of average and water year-to-date precipitation is 100% of average. Reservoir storage at the end of March was 125% of average compared to 106% last year. Current streamflow forecasts range from 89% of average for White River near Meeker to 118% for the North Platte River near Northgate. Yampa, White & North Platte River Basins Mountain Snowpack Snow Water Equivalent (Inches) 40 35 30 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 140 120 Percent of Average 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date April May 21 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Laramie North Platte Total Laramie & North Platte Elk Yampa White Total Yampa & White Little Snake Basin-Wide Total # of Sites Last Year % % Median Median 2 108 124 8 115 123 10 114 123 2 103 101 9 111 116 3 97 128 11 107 118 8 117 118 26 111 120 *SWE values calculated using first of month SNOTEL data and snow course measurements 22 End of March Reservoir Storage Percent Average 140% Percent Capacity 120% 100% 80% 60% 40% 20% 0% STAGECOACH RESERVOIR NR OAK CREEK YAMCOLO RESERVOIR BASINWIDE Reservoir Storage End of March 2020 Current Last Year Average Capacity (KAF) (KAF) (KAF) (KAF) STAGECOACH RESERVOIR NR OAK C 34.1 31.2 27.2 36.5 YAMCOLO RESERVOIR 8.1 4.7 6.6 8.7 BASINWIDE 42.2 35.9 33.8 45.2 Number of Reservoirs 2 2 2 2 Reservoir 23 YAMPA-WHITE-NORTH PLATTE RIVER BASINS Water Supply Forecasts April 1, 2020 Forecast Exceedance Probabilities Forecast Forecast Drier Future Conditions Wetter PDint Period Labels on chart represent volumes of water expressed in thousand acre-feet. 148 220 265 315 380 North Platte nr Apr-Jul I I Northgate 225 162 240 290 345 425 Apr-Sep I I 250 72 102 122 142 171 Laramie and Apr-Jul I Pioneer nr 115 79 111 133 155 187 Apr-Sap Yampa ab Apr-Jul I Stagecoach 23 Resewo'r 200 240 270 300 350 Yampa at Apr-Jul I Steamboat 260 Spr'?Milner Apr-Jul I 320 45 60 72 85 106 Elkhead Ck ab Apr-Jul I Long Gulch 73 740 895 1,010 1,130 1,320 Yampa nr Apr-Jul I I Maybell 935 114 138 1 55 173 200 Little Snake nr Apr-Jul I Slater 155 199 275 335 400 505 Little Snake nr Apr?Jul I Dixon 345 210 290 350 415 525 Little Snake nr Apr-Jul I Lily 345 172 215 250 285 340 White nr Apr-Jul I Meeker 280 I I I I I I 50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150% 160% 170% Percent of Average (30 Yr Period) Legend 95Exceedance Exceedance Exceedance Exceedance Exceedance There is a 95%!90% chance that There is a 70% chance that There ls a 50% chance that There ls a 30% chance that There is a 10%15% chance that flows will exceed volume ?ows will exceed this volume flows will exceed this volume ?ows will exceed this volume ?ows will exceed this volume Perl Stream?ow KAF (Year) Stream?ow KAF Stream?ow KAF (Year) When selected, the following historic streamflow values and statistics will be shown. 00' of Record Minimum 1981-2010 Norma! Observed Stream?ow KAF Period of Record Maximum Some forecasts may be for volumes that are regulated or in?uenced by diversions and water management. 24 ARKANSAS RIVER BASIN April 1, 2020 Snowpack in the Arkansas River basin is above normal at 105% of the median. Precipitation for March was 62% of average which brings water year-to-date precipitation to 85% of average. Reservoir storage at the end of March was 92% of average compared to 90% last year. Current streamflow forecasts range from 66% of average for Grape Creek near Westcliffe to 104% for the Arkansas River at Salida. Arkansas River Basin Mountain Snowpack Snow Water Equivalent (Inches) 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 140 120 Percent of Average 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date April May 25 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Upper Arkansas Cucharas & Huerfano Purgatoire Basin-Wide Total Last Year % # of Sites % Median Median 4 120 145 3 88 169 2 79 173 9 105 148 *SWE values calculated using first of month SNOTEL data and snow course measurements 26 End of March Reservoir Storage Percent Average 160% Percent Capacity 140% 120% 100% 80% 60% 40% 20% 0% Reservoir Storage End of March 2020 Reservoir ADOBE CREEK RESERVOIR CLEAR CREEK RESERVOIR CUCHARAS RESERVOIR GREAT PLAINS RESERVOIR HOLBROOK LAKE HORSE CREEK RESERVOIR JOHN MARTIN RESERVOIR LAKE HENRY MEREDITH RESERVOIR PUEBLO RESERVOIR TRINIDAD LAKE TURQUOISE LAKE TWIN LAKES RESERVOIR BASINWIDE Number of Reservoirs Current Last Year Average Capacity (KAF) (KAF) (KAF) (KAF) 47.6 8.9 50.4 62.0 8.2 7.6 7.6 11.4 40.0 150.0 3.6 0.3 4.7 7.0 3.4 26.8 12.8 27.0 122.9 175.8 155.0 616.0 3.6 7.3 7.3 9.4 39.6 32.1 29.2 42.0 258.7 235.6 205.8 354.0 24.3 22.9 28.5 167.0 52.8 46.2 73.5 127.0 42.2 32.0 49.6 86.0 606.8 595.4 624.4 1698.8 11 11 11 13 27 ARKANSAS RIVER BASIN Water Supply Forecasts April 1, 2020 Forecast Exceedance Probabilities Forecast Forecast Drier Future Conditions Wetter POW Period Labels on chart represent volumes of water expressed in thou sand acre-feet. 13 17 21 25 32 Chalk ox nr Apr-Jul I Nethrop 21 15 21 25 30 38 Apr?Sep I 26 230 240 250 260 270 Arkansas at Apr-Jul Fl Salida 240 265 285 300 315 340 Apr-Sep 295 3.5 7.7 11 13 18 Grape Ck nr Apr-Jul I Westcliffe 15 4.6 9.7 13 17 22 Apr-Sap I 20 196 275 335 400 510 Arkansas ab Apr-Jul I Pueblo 350 250 350 425 510 650 Apr-Sep Huerfano nr Apr?Jul Redwing Apr-Sap Cucharas nr Apr-Jul La Vote 12 5.8 8 11 14 18 Apr-Sap 1'4 11 21 30 40 58 Purgatoire at Apr-Jul I Trinidad 35 14 28 40 55 80 Apr-Sap Mar-Jul 37 20% 40% 60% 80% 100% 120% 140% 160% 180% Percent of Average (30 Yr Period) Legend Exceedance Exceedance Exceedance Exceedance Exceedance There is a 95%i90% chance that flows will exceed this volume There is a 10%i5% chance that flows exceed this volume There is a 30% chance that flows exceed this volume There is a 50% chance that flows Will exceed this volume There is a 70% chance that tlows exceed this volume Period of Record Minimum When selected, the following historic stream?ow values and statistics will be shown. Period of Record Maximum Streamflow KAF (Year) 1981 ?2010 Normal Observed Stream?ow KAF Streemfi'ow KAF Streem?ow KAF Year) Some forecasts may be for volumes that are regulated or influenced by diversions and water management. 28 UPPER RIO GRANDE RIVER BASIN April 1, 2020 Snowpack in the Upper Rio Grande River basin is normal at 100% of median. Precipitation for March was 80% of average which brings water year-to-date precipitation to 76% of average. Reservoir storage at the end of March was 83% of average compared to 78% last year. Current streamflow forecasts range from 43% of average for San Antonio River at Ortiz to 88% for Saguache Creek near Saguache. Upper Rio Grande Basin Mountain Snowpack Snow Water Equivalent (Inches) 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *Note: the mountain snowpack time series is calculated using a different method resulting in slightly different median and basin wide SWE values compared to the official monthly percent-of-median value. The SWE values are also calculated using daily SNOTEL data only. Mountain Precipitation 160 140 Percent of Average 120 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date April May 29 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Alamosa Creek Conejos & Rio San Antonio Culebra & Trinchera Creek Upper Rio Grande Basin-Wide Total Last Year % # of Sites % Median Median 1 80 149 2 131 82 3 103 121 5 105 160 11 100 147 *SWE values calculated using first of month SNOTEL data and snow course measurements 30 End of March Reservoir Storage Percent Average 350% Percent Capacity 300% 250% 200% 150% 100% 50% 0% CONTINENTAL RESERVOIR PLATORO RESERVOIR RIO GRANDE RESERVOIR SANCHEZ RESERVOIR SANTA MARIA RESERVOIR TERRACE RESERVOIR BEAVER RESERVOIR BASINWIDE Reservoir Storage End of March 2020 Reservoir CONTINENTAL RESERVOIR PLATORO RESERVOIR RIO GRANDE RESERVOIR SANCHEZ RESERVOIR SANTA MARIA RESERVOIR TERRACE RESERVOIR BEAVER RESERVOIR BASINWIDE Number of Reservoirs Current Last Year Average Capacity (KAF) (KAF) (KAF) (KAF) 16.7 16.5 5.8 27.0 18.4 18.9 24.2 60.0 4.0 2.2 19.1 51.0 9.1 8.6 28.1 103.0 21.8 23.7 10.9 45.0 9.0 5.5 8.2 18.0 4.2 3.5 4.3 4.5 83.1 78.8 100.6 308.5 7 7 7 7 31 UPPER RIO GRANDE BASIN Water Su pply Fcrecaets April 1I 2:120 Eeceedsnee L?lil Iti?? Forecast Fereceet - - - - - - Dner - - - - - - - Fulure Weller - - - - - - :1 p?ir? F?Bri?d Labels en chen represent volumes cl water expressed I "l Ihcusend acre-feel. 54 TU 31 93 113- Flie Erende el Apr-Jul I 1? Thirty Mile Bridge 50 T9 '54 11'] 13B Apr-Sen I T29 15-4 2'05 245 290 355 Rio Grande at Apr-Sec I Wagcn Wheel 3.11Grende Apr-Sec I i at South Fork 12? 230 3130 355 415 505 Rio Grande nr Apr-Sen Del Nerle 51'5 15 32 23 3?3 44 Segueche CH nr Apr-Sap I Seguache 32 3-9 45 52 5-2 Alamesa Cl: ac Apr-Sap I Terrace 5.3 ResemJara cr. nr Apr-Jul I Capulin 3.2 1D 11 14 cm: at- Aer-See I Tumere Ranch 13 5.2 5.9 12 15 22 Sangre De Apr-Sap I Cn?ete CR '15 213% 315% 41.1% 56% 66% 71.1% 551% 915% 1c'c% 111.1% 19.13% 13.13% 141':% Percent ef Average {30 ?fr Period} Legend 9% or 90% we 511% 311% 111% or 1% Exceede nee Exceedonoe Enceeclenoe Exceeda nee There 15 a Q??m chance that There re 3 chenee lhel There tee ohenee that There 15 30!: cleaned lhel There-e a chance that Flows will exceed this eelume ?me w-I exceed volume hmwill exceed lhie volume ?ows eroeed the velLa-me ?ewewll E?l-G-E-Ed1hr5 'rdurne 1I.I'I1'hen selected. the slrea m?cw values and statistics will be shown- Penec? of Record Mrmmurn 1931-26113 Normal Observed Slream?ew RAF Perlod checcro' Maximum Srreem?ew KAF Wear} Streem?ow RAF RAF Wear? Some loreceele may be [or volumes that are regulated or in?uenced by diversions and water managemenl. 32 UPPER RID GRANDE BASIN Water Bu Forecasts April 1. 2920 Forecast Esceedence Probe hilities Forecast Forecast It Dner - - - - - - - Future Conditions Wetter Point Peri?d Labels on chart represent volumes of water expressed In thousand acre-feelFort AprvSep I Garland 1'3 29 35 49 45 52 Plaloro Reservoir In?Apr-Eep I I 52' $5 103 125 143 Conejos nr Apr-Esp I Mogote 194 3.6 5.4 5.3 11 San Antonio at Apr-Sen I UniLos Pines or Apr-Sap I Cll'liI :3 1D 15 1B 22 28 Culebra Cit at Apr-Sen I Luis 23 4.1 9.3 9.9 13 Coelilla Ct: bl Apr-Jul 1 Coslilla Darn 1'0 3.1 14 1E 23 32 Costilla Ck nr Apr-Jul I Costille 2e 20% 35% 49% stirs sons Hie arias odes mos: 11ers 12ers. mos. 140% Percent of Average [34] Yr Period} Legend or 90% 59% 30% 19% or 51"! Esoeedanoe Exceeds nce Exceedancs Esceedanoe Esoeedance Thom re 9 95939992. chaos-J the1 There a chance that more re a 599i- that There is a 39% char-oomm There Is a chance that ?ows on" exceed this vqurn-e ?ours IMII exceed ills-lune ?ows wil eroeed the volurrs ?owswnesoeed the tl?dumt! How-s wil ecceed1hrs volume When selected. the tollowlng hlstorio stream?ow 1.ralues and will be show- Period of Record Mrmmum 1931-2010 rlni'orroelI Observed Stream?ow RAF Period of Record Maximum Streamline Freer) Stream?ow KAF Stream?ow KAF (Year) Some forecasts may be for volumes. that are regulated or in?uenoed by diversions and water management. 33 SAN MIGUEL, DOLORES, ANIMAS, AND SAN JUAN RIVER BASINS April 1, 2020 Snowpack in the combined southwest river basins is at 99% of median. Precipitation for March was 114% of average which brings water year-to-date precipitation to 80% of average. Reservoir storage at the end of March was 104% of average compared to 58% last year. Current streamflow forecasts range from 61% of average for the Navajo Reservoir Inflow to 80% for the Animas River at Durango. San Miguel, Dolores, Animas & San Juan River Basins Mountain Snowpack Snow Water Equivalent (Inches) 35 30 25 20 15 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct 5 50% Exceedance *SWE values calculated using daily SNOTEL data only Mountain Precipitation 160 140 Percent of Average 120 100 80 60 40 20 0 Oct Nov Dec Monthly Jan Feb Mar Year-to-date April May 34 Watershed Snowpack Analysis April 1st, 2020 Sub-Basin Animas Dolores San Miguel San Juan Basin-Wide Total Last Year % # of Sites % Median Median 9 104 169 6 159 99 3 93 149 3 94 143 20 99 159 *SWE values calculated using first of month SNOTEL data and snow course measurements 35 End of March Reservoir Storage Percent Average 160% Percent Capacity 140% 120% 100% 80% 60% 40% 20% 0% GROUNDHOG RESERVOIR JACKSON GULCH RESERVOIR LEMON RESERVOIR MCPHEE RESERVOIR NARRAGUINNEP RESERVOIR VALLECITO RESERVOIR TROUT LAKE RESERVOIR BASINWIDE Reservoir Storage End of March 2020 Reservoir GROUNDHOG RESERVOIR JACKSON GULCH RESERVOIR LEMON RESERVOIR MCPHEE RESERVOIR NARRAGUINNEP RESERVOIR VALLECITO RESERVOIR TROUT LAKE RESERVOIR BASINWIDE Number of Reservoirs Current Last Year Average Capacity (KAF) (KAF) (KAF) (KAF) 16.3 0.3 12.5 22.0 3.9 2.0 5.0 10.0 17.7 7.3 21.7 40.0 280.5 168.2 282.2 381.0 15.4 12.4 16.1 19.0 83.5 40.3 63.3 126.0 1.9 2.0 1.4 3.2 419.3 232.4 402.2 601.2 7 7 7 7 36 SAN MIGUEL-DOLORES-ANIMAS-SAN JUAN RIVER BASINS Water Supply Forecasts April 1, 2020 Forecast Exceedance Probabilities Forecast Forecast Drier Future Conditions Wetter Point Period Labels on chart represent volumes of water expressed in thousand acre-feet. 125 156 179 205 240 Dolores at Apr-Jul I Dolores 245 133 171 200 230 280 Dolores bl Apr-Jul I Mcphee 295 Resem? 57 74 87 101 124 San Miguel nr AprnJul I Placerville 123 1.5 1.9 2.2 2.5 3 Cone Reservoir Apr-Jul I Inlet 3.1 8.2 10 12 13 15 Gurley Reservoir Apr-Jul I Inlet 16 1.1 1.6 2 2.4 3.1 Lilylands Aprcui *7 Reservoir Inlet 2] 23 30 35 40 49 Rio Bianco bl Apr-Jul I I Blanco Diversion 54 2? 34 40 46 56 Navajo bl Oso Apr-Jul I I Diversion Dam 55 ?r Chrom" 151 196 230 265 325 San Juan nr ApreJul I Carracas 330 96 121 140 160 192 Piedra nr Apr-Jul I I Arboles 210 102 127 145 164 195 Los Pinos nr Apr-Jul I Bayfield 194 295 385 450 525 640 San Juan nr Apr-Jul I I Archuleta 735 240 290 330 370 435 Animas at Apr-Jul I Durango 415 29 35 40 46 54 Florida bl Apr?Jul I Lemon Reservoir 55 ?r Durango 13 16 1a 20 24 La Plata at Apr-Jul I Hesperus 23 12 17 20 24 29 Mancos nr Apr-Jul I Mancos 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% Percent of Average (30 Yr Period) Legend 95Exceedance Exceedance Exceedance Exceedance Exceedance There is a ssweoru chance that There is a 70% chance that There is 50% chance that There is a 30% chance that There is a 10%1591 chance that ?ows wiil exceed this volume ?ows wiil exceed this volume flows will exceed this volume ?ows will exceed this volume tlows will exceed this volume When selected, the following historic streamflow values and statistics wiil be shown. Period of Record Minimum 1981-2010 Observed Streamfi?ow KAF Period of Record Maxrmum Stream?ow KAF (Year) Stream?ow KAF Stream?ow KAF (Year) Some forecasts may be for volumes that are regulated or influenced by diversions and water management. 37 How to Read Snowpack Graphs The graphs show snow water equivalent (SWE) (in inches), using daily SNOTEL data. for the October 1 through September 30 water year. Basin “observed” SWE values are computed using SNOTEL sites which are characteristic of the snowpack of the particular basin. The SWE observations at these sites are averaged and normalized to produce these basin snowpack graphs. Current water year is represented by the heavy red line terminating on the last day the graphic was updated. Historical observed percentile range is shown as a gray background area on the graph. Shades of gray indicate maximum, 90 percentile, 70 percentile, 50 percentile (solid black line), 30 percentile, 10 percentile, and minimum for the period of record. 50 % Excedance Projection: The most probabilistic snowpack projection, based on the median snowpack is projected forward from the end of the current period to the end of the current water year. For more detailed information on these graphs visit: http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_062291.pdf South Platte River Basin Mountain Snowpack Historical Observed Percentiles: Maximum (on top), 90, 70, 50 (median), 30, 10, Minimum (on bottom). 25 20 15 50 % Exceedance Projection 10 Historic Snowpack Range Median Snowpack Current Snowpack Sep Aug Jul Jun May Apr Mar Feb Jan Dec 0 Nov 5 Oct Snow Water Equivalent (Inches) 30 50% Exceedance 38 How Forecasts Are Made For more water supply and resource management information, contact: Brian Domonkos Snow Survey Supervisor USDA, Natural Resources Conservation Service Denver Federal Center, Bldg 56, Rm 2604 PO Box 25426 Denver, CO 80225-0426 Phone (720) 544-2852 Website: http://www.nrcs.usda.gov/wps/portal/nrcs/main/co/snow/ 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 it 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 prepare 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 uncertain 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. 39 Interpreting the Forecast Graphics These graphics provide a new way to visualize the range of streamflows represented by the forecast exceedance probabilities for each forecast period. The colors in the bar for each forecast point indicate the exceedance probability of the forecasts and the vertical lines on the bar signify the five published forecast exceedance probabilities. The numbers displayed above the color scale represent the actual forecasted streamflow volume (in KAF) for the given exceedance probability. The horizontal axis provides the percent of average represented by each forecast and the gray line centered above 100% represents the 1981-2010 historical average streamflow. The position of the gray line relative to the color scale provides a benchmark for considering future streamflows. If the majority of the forecast range is to the right of the gray line, there is a higher likelihood of above average streamflow volumes during the provided forecast period. Conversely, if the majority of the color bar is to the left of the average mark, below average volumes are more likely. The horizontal span of the forecasts offers an indication of the uncertainty in a given forecast: when the bar spans a large horizontal range, the forecast skill is low and uncertainty is high; when the bar is narrow in width, the forecast skill is higher and uncertainty lower. 40 Denver Federal Center, Bldg 56, Rm 2604 PO Box 25426 Denver, CO 80225-0426 In addition to the water supply outlook reports, water supply forecast information for the Western United States is available from the Natural Resources Conservation Service and the National Weather Service monthly, January through June. The information may be obtained from the Natural Resources Conservation Service web page at http://www.wcc.nrcs.usda.gov/wsf/westwide.html Issued by Released by Matthew J. Lohr Chief, Natural Resources Conservation Service Farm Production and Conservation Mission Area U.S. Department of Agriculture Clint Evans State Conservationist Natural Resources Conservation Service Lakewood, Colorado Colorado Water Supply Outlook Report Natural Resources Conservation Service Lakewood, CO 41