Lake Powell Water Supply Outlook, May 1, 2021

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by Ashley Nielson
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Lake Powell Sub-Basin Summaries




*Median of forecasts within each basin.





*Median of forecasts within each basin.







*Median of forecasts within each basin.




Upper Green Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Yampa/White Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Duchesne Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Lower Green Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Upper Colorado Mainstem Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Gunnison Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Dolores Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

San Juan Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.


Upper Green Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Green
Daniel, Nr, Warren Bridge, At April-July126 150 169 69 194 215
May-July113 137 156 69 181 200
Pine Ck
Fremont Lk, Abv April-July46 56 63 64 69 80
May-July45 55 62 65 68 79
New Fork
Big Piney, Nr April-July89 142 170 48 198 255
May-July73 126 154 47 182 240
Green
Fontenelle Reservoir, Fontenelle, Nr April-July225 315 380 52 445 535
May-July173 260 325 51 390 480
Big Sandy
Farson, Nr April-July17.7 22 27 52 32 42
May-July16 20 25 52 30 40
Green
Green River, Wy, Nr April-July220 305 375 51 450 530
May-July170 255 325 51 400 480
Hams Fork
Frontier, Nr, Pole Ck, Blo April-July24 27 31 57 37 44
May-July19 22 26 54 32 39
Viva Naughton Reservoir April-July30 33 37 50 44 55
May-July23 26 30 48 37 48
Blacks Fork
Robertson, Nr April-July32 39 46 52 56 67
May-July30 37 44 52 54 65
Ef Smiths Fork
Stateline Reservoir, Robertson,nr April-July11.8 13.7 16.2 62 18.9 23
May-July11 12.9 15.4 59 18.1 22
Green
Flaming Gorge Reservoir April-July270 365 450 46 550 670
May-July200 295 380 45 480 600


Yampa/White Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Yampa
Stagecoach Rsvr, Abv April-July9 10.7 11.7 51 12.7 14.7
May-July5.3 7 8 50 9 11
Steamboat Springs April-July80 95 110 42 132 167
May-July70 85 100 45 122 157
Elk
Milner, Nr April-July134 157 174 54 194 230
May-July115 138 155 53 175 210
Elkhead Ck
Long Gulch, Abv, Hayden, Nr April-July14.7 18.2 21 29 27 34
May-July9 12.5 15 30 21 28
Yampa
Maybell, Nr April-July260 315 365 39 425 540
May-July220 275 325 42 385 500
Little Snake
Slater, Nr April-July58 69 80 51 92 113
May-July50 61 72 52 84 105
Dixon, Nr April-July106 127 148 43 177 215
May-July88 109 130 44 159 195
Lily, Nr April-July96 122 148 43 177 220
May-July78 104 130 45 159 200
Yampa
Deerlodge Park April-July355 430 510 41 605 755
May-July300 375 455 45 550 700
White
Meeker, Nr April-July106 121 136 49 149 178
May-July85 100 115 47 128 157
Watson, Nr April-July106 124 136 49 151 183
May-July85 103 115 49 130 162


Duchesne Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Big Brush Ck
Vernal, Nr, Red Fleet Res, Abv April-July6.1 7.6 9.1 43 10 14
May-July5.4 6.9 8.4 46 9.3 13.3
Ashley Ck
Vernal, Nr April-July14.6 17 20 40 22 31
May-July13.6 16 19.3 41 21 30
West Fork Duchesne
Vat Diversion, Blo April-July3.7 4.5 5.5 30 6.2 7.8
May-July3 3.8 4.8 28 5.5 7.1
Duchesne
Tabiona, Nr April-July38 43 50 46 56 59
May-July32 37 44 45 50 53
Rock Ck
Upper Stillwater Reservoir April-July27 33 38 51 43 48
May-July23 29 34 48 39 44
South Fork Rock Ck
Docs Div, Blo April-July1.7 2.3 2.9 40 3.3 3.8
May-July1.4 2 2.6 38 3 3.5
Rock Ck
Mountain Home, Nr April-July33 40 47 53 53 59
May-July28 35 42 50 48 54
Currant Ck
Currant Ck Reservoir April-July2.6 3.5 4.8 24 5.5 7
May-July1.8 2.7 4 23 4.7 6.2
Strawberry
Strawberry Reservoir, Soldier Springs April-July9.8 12 14.5 20 16 17.8
May-July5.7 7.9 10.4 17.9 11.9 13.7
Starvation Reservoir, Duchesne, Nr April-July13 22 30 27 34 40
May-July6.5 15.5 23 25 27 33
Duchesne
Duchesne, Nr, Knight Div, Abv April-July70 87 99 51 110 116
May-July60 77 89 50 100 106
Lake Fork
Moon Lake Reservoir, Mtn Home, Nr April-July19 24 27 41 31 39
May-July17 22 25 40 29 37
Yellowstone
Altonah, Nr April-July19.5 23 26 43 29 37
May-July16.9 20 23 40 26 34
Whiterocks
Whiterocks, Nr April-July14 17.4 22 41 24 30
May-July12.5 15.9 21 41 23 29
Uinta
Neola, Nr April-July18.5 25 30 41 33 46
May-July16.3 23 28 39 31 44
Duchesne
Myton April-July45 64 81 25 96 122
May-July27 46 63 21 78 104
Randlett, Nr April-July53 73 89 23 105 131
May-July34 54 70 20 86 112


Lower Green Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
White
Blo Tabbyune Ck, Soldier Summit, Nr April-July0.7 0.94 1.5 9.5 2 3.5
May-July0.43 0.67 1.2 10.1 1.7 3.2
Fish Ck
Scofield, Nr, Reservoir, Abv April-July6 8.5 10 33 11 12.1
May-July4.8 7.3 8.8 34 9.8 10.9
Price
Scofield Reservoir, Scofield, Nr April-July7.5 10 11.9 29 13 14.3
May-July5.5 8 9.9 28 11 12.3
Green
Green River, Ut April-July710 940 1110 38 1350 1660
May-July550 780 950 37 1190 1500
Huntington Ck
Electric Lake April-July2.1 3 3.5 26 4 5.1
May-July1.7 2.6 3.1 26 3.6 4.7
Power Plant, Blo April-July14 16.1 16.8 42 17.8 20
May-July13.1 15.2 15.9 43 16.9 19.1
Seeley Ck
Joes Vly Reservoir, Orangeville, Nr April-July11 14.9 17.1 31 18.2 24
May-July9.7 13.6 15.8 30 16.9 23
Ferron Ck
Ferron, Nr April-July7 11.2 12.5 33 15.3 19.9
May-July6 10.2 11.5 33 14.3 18.9
Muddy Ck
Emery, Nr April-July3.6 5.2 5.8 29 6.5 7.8
May-July2.9 4.5 5.1 28 5.8 7.1


Upper Colorado Mainstem Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Colorado
Lake Granby, Granby, Nr April-July120 140 160 73 180 200
May-July106 126 146 71 166 186
Willow Ck
Willow Ck Reservoir, Granby, Nr April-July20 26 32 68 39 46
May-July12.2 18.2 24 56 31 38
Fraser
Winter Park April-July11.5 13 14.5 75 16.5 18.5
May-July10.7 12.2 13.7 74 15.7 17.7
Williams Fork
Williams Fork Reservoir, Parshall April-July44 51 58 60 66 74
May-July38 45 52 58 60 68
Muddy Ck
Wolford Mountain Reservoir April-July14 20 25 46 30 36
May-July10.3 16.3 21 46 26 32
Blue
Dillon Reservoir April-July60 74 88 54 100 115
May-July53 67 81 53 93 108
Green Mtn Reservoir April-July110 130 150 55 170 190
May-July96 116 136 53 156 176
Colorado
Kremmling, Nr April-July400 460 520 60 600 700
May-July340 400 460 59 540 640
Eagle
Gypsum, Blo April-July110 135 160 48 190 220
May-July98 123 148 47 178 210
Colorado
Dotsero, Nr April-July600 680 770 55 900 1000
May-July510 590 680 53 810 910
Frying Pan
Ruedi Reservoir, Basalt, Nr April-July60 72 85 61 100 115
May-July54 66 79 61 94 109
Roaring Fork
Glenwood Springs April-July280 320 360 52 420 480
May-July250 290 330 52 390 450
Colorado
Glenwood Springs, Blo April-July900 1030 1160 55 1350 1500
May-July775 905 1040 54 1230 1380
Cameo, Nr April-July900 1050 1200 51 1400 1600
May-July775 925 1080 50 1280 1480
Plateau Ck
Cameo, Nr April-July15 23 32 26 43 55
May-July9.5 17.5 26 25 37 49
Colorado
Cisco, Nr April-July1200 1500 1850 42 2200 2600
May-July975 1270 1620 42 1970 2370
Lake Powell, Glen Cyn Dam, At April-July1140 1640 2000 28 2690 3790
May-July850 1350 1710 28 2400 3500


Gunnison Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Taylor
Taylor Park Reservoir April-July45 51 58 59 66 75
May-July38 44 51 57 59 68
Almont April-July65 75 86 55 96 110
May-July56 66 77 55 87 101
East
Almont April-July75 90 105 58 115 130
May-July65 80 95 57 105 120
Gunnison
Gunnison, Nr April-July140 170 200 54 225 250
May-July120 150 180 54 205 230
Tomichi Ck
Gunnison April-July14 21 28 38 36 44
May-July7.4 14.4 21 34 29 37
Lake Fork
Gateview April-July40 52 65 53 75 90
May-July35 47 60 52 70 85
Gunnison
Blue Mesa Reservoir April-July240 290 340 50 400 460
May-July193 245 295 49 355 415
Morrow Point Reservoir April-July260 310 365 49 420 480
May-July210 260 315 48 370 430
Crystal Reservoir April-July300 350 400 48 470 540
May-July245 295 345 47 415 485
Muddy Ck
Paonia Reservoir, Bardine, Nr March-June16 22 28 29 35 42
April-July16 22 28 29 35 42
May-June9.5 15.5 21 30 28 35
May-July11 17 23 31 30 37
Nf Gunnison
Somerset, Nr April-July95 115 135 46 150 170
May-July77 97 117 49 132 152
Surface Ck
Cedaredge April-July3 4 5 30 6.5 8
May-July1.8 2.8 3.8 27 5.3 6.8
Uncompahgre
Ridgway Reservoir April-July34 41 48 48 56 64
May-July29 36 43 47 51 59
Colona April-July34 43 52 38 63 74
May-July28 37 46 38 57 68
Delta April-July12 19 26 23 35 44
May-July2.8 9.8 16.8 18 26 35
Gunnison
Grand Junction, Nr April-July380 500 600 41 700 820
May-July290 410 510 41 610 730


Dolores Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
Dolores
Dolores April-July51 66 78 32 91 111
May-July40 55 67 34 80 100
Mcphee Reservoir April-July52 67 81 27 92 117
May-July40 55 69 31 80 105
San Miguel
Placerville, Nr April-July41 48 53 41 59 71
May-July35 42 47 42 53 65
Dolores
Cisco, Nr April-July61 77 91 16 112 141
May-July40 56 70 17 91 120


San Juan Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		30%
Exceedance
Volume		10%
Exceedance
Volume
San Juan
Pagosa Springs April-July103 114 122 57 133 150
May-July75 86 94 52 105 122
Carracas, Nr April-July173 190 205 54 220 255
May-July128 145 160 53 175 210
Navajo Reservoir, Archuleta, Nr April-July265 295 325 44 345 410
May-July186 215 245 43 265 330
Farmington April-July330 365 405 37 460 610
May-July250 285 325 37 380 530
Bluff, Nr April-July300 335 375 34 440 590
May-July220 255 295 35 360 510
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July29 32 34 63 38 43
May-July21 24 26 58 30 35
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July34 37 39 60 43 49
May-July26 29 31 57 35 41
Little Navajo
Oso Div Dam,bl,chromo,nr April-July3.1 3.5 3.9 51 4.3 5.1
May-July2 2.4 2.8 52 3.2 4
Piedra
Arboles, Nr April-July68 81 90 43 100 119
May-July46 59 68 44 78 97
Los Pinos
Vallecito Reservoir, Bayfield, Nr April-July71 80 92 47 102 119
May-July57 66 78 46 88 105
Animas
Durango April-July118 145 164 40 193 250
May-July100 127 146 40 175 230
Florida
Lemon Reservoir, Durango, Nr April-July14.5 17 19.5 35 23 28
May-July12 14.5 17 35 20 25
La Plata
Hesperus April-July5 6.1 7 30 8.2 10.5
May-July3.5 4.6 5.5 30 6.7 9
Mancos
Mancos, Nr April-July5.5 6.3 7.5 24 8.5 10.5
May-July4 4.8 6 25 7 9

Differences between the full period forecasts and the residual forecasts may not exactly equal the actual observed volumes due to rounding conventions (see Definitions section).

Green End of Month Reservoir Contents (kaf)

EOM
Contents		Percent
EOM
Average		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Average		EOM
Average		Usable
Capacity
untitled Green
Fontenelle Reservoir, Fontenelle, Nr 125.2 100 37 145.1 116 125.0 334.0
untitled Big Sandy
Big Sandy Reservoir, Nr Farson 11.5 54 30 26.7 125 21.3 38.3
Blacks Fork
Meeks Cabin 8.4 51 28 15.7 95 16.5 29.9
untitled Ef Smiths Fork
Stateline Reservoir, Robertson,nr 4.5 69 32 6.6 102 6.5 13.9
untitled Green
Flaming Gorge Reservoir 3178.3 105 85 3207.0 105 3040.4 3749.0
untitled Strawberry
Strawberry Reservoir, Soldier Springs 926.2 137 84 986.1 146 676.1 1105.9
Starvation Reservoir, Duchesne, Nr 164.9 109 100 165.1 109 151.9 165.3
untitled Rock Ck
Upper Stillwater Reservoir 4.0 140 13 2.4 84 2.9 31.4
untitled Lake Fork
Moon Lake Reservoir, Mtn Home, Nr 16.0 58 44 27.3 99 27.6 36.5
untitled Big Brush Ck
Red Fleet Reservoir, Vernal, Nr 16.7 83 65 21.7 108 20.1 25.7
untitled Price
Scofield Reservoir, Scofield, Nr 36.8 111 56 53.6 162 33.0 65.8
untitled Seeley Ck
Joes Vly Reservoir, Orangeville, Nr 37.4 94 60 47.8 121 39.6 62.5
untitled Huntington Ck
Electric Lake 18.4 98 58 22.6 121 18.7 31.5
untitled
TOTAL 4548.3 109 80 4727.7 113 4179.6 5689.6


Upper Colorado End of Month Reservoir Contents (kaf)

EOM
Contents		Percent
EOM
Average		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Average		EOM
Average		Usable
Capacity
untitled Colorado
Lake Granby, Granby, Nr 350.2 112 71 405.6 130 311.8 490.3
untitled Willow Ck
Willow Ck Reservoir, Granby, Nr 8.0 104 88 8.9 116 7.7 9.1
untitled Williams Fork
Williams Fork Reservoir, Parshall 61.0 100 63 75.6 124 60.9 96.9
untitled Muddy Ck
Wolford Mountain Reservoir 52.8 111 80 54.6 114 47.7 66.0
untitled Blue
Dillon Reservoir 202.8 95 80 231.4 108 213.6 254.0
Green Mtn Reservoir 54.5 85 37 67.5 106 63.9 146.9
untitled Homestake Ck
Homestake Reservoir 12.2 65 28 24.0 128 18.8 43.0
untitled Frying Pan
Ruedi Reservoir, Basalt, Nr 59.6 95 58 65.3 104 62.6 102.0
untitled Plateau Ck
Vega Reservoir, Collbran, Nr 8.3 45 25 18.1 98 18.3 32.9
untitled Taylor
Taylor Park Reservoir 63.6 104 60 72.6 119 61.2 106.2
untitled Gunnison
Blue Mesa Reservoir 365.2 80 44 509.6 111 457.1 827.9
Morrow Point Reservoir 102.6 92 88 106.8 96 111.8 117.0
Crystal Reservoir 16.9 101 96 17.4 104 16.7 17.5
untitled Muddy Ck
Paonia Reservoir, Bardine, Nr 10.3 160 62 10.8 168 6.4 16.7
untitled Uncompahgre
Ridgway Reservoir 57.8 87 70 66.1 99 66.6 83.0
untitled Dolores
Mcphee Reservoir 176.4 55 46 276.0 85 323.0 381.1
untitled
TOTAL 1602.1 87 57 2010.2 109 1848.0 2790.6
Colorado
Lake Powell 8504.5 50 35 11685.3 68 17122.8 24322.0
untitled
TOTAL 8504.5 50 35 11685.3 68 17122.8 24322.0


San Juan End of Month Reservoir Contents (kaf)

EOM
Contents		Percent
EOM
Average		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Average		EOM
Average		Usable
Capacity
untitled Los Pinos
Vallecito Reservoir, Bayfield, Nr 56.6 76 45 95.1 128 74.0 125.4
untitled San Juan
Navajo Reservoir, Archuleta, Nr 1044.6 77 62 1296.8 95 1361.0 1696.0
untitled Florida
Lemon Reservoir, Durango, Nr 13.2 55 33 19.8 82 24.1 39.8
untitled
TOTAL 1114.4 76 60 1411.7 97 1459.0 1861.2

Precipitation Maps




Definitions

10% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 10% chance of being exceeded. Previously referred to as "Reasonable Maximum Forecast".

50% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 50% chance of being exceeded. Previously referred to as "Most Probable Forecast".

90% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 90% chance of being exceeded. Previously referred to as "Reasonable Minimum Forecast".

Acre-Foot (af): The volume equal to one acre covered one foot deep (43,560 cubic feet). See kaf below.

Average: The arithmetic mean. The sum of the values divided by the number of values. Values from 1981-2010 are used for this publication.

Categories: Much Above Average=Greater than 130%, Above Average=111-130%, Near Average=90-110%, Below Average=70-89%, Much Below Average=Less than 70%.

CBRFC: Colorado Basin River Forecast Center.

Forecast Period: The period from April 1 through July 31, unless otherwise noted.

kaf: Thousand Acre-Feet. See Acre-Foot above.

Inflow: The volume of water that flows into a reservoir or lake.

Median: The middle value of an ordered set of values. Half of the values are higher and half of the values are lower. When the set contains an even number of values the median is the average of the two middle numbers.

NOAA: National Oceanic and Atomospheric Administration.

NWS: National Weather Service.

Rounding Conventions:
RangeRound to
0-1.990.01
2.0-19.90.1
20-1991.0
200-9995.0
1000+3 significant digits


Streamflow: The volume of water that flows past a specific stream site.

Water Year: The 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends. Thus, the year ending September 30, 2008, is called the "2008 water year."


Additional Information

Water supply forecasts take into consideration present hydrometeorological conditions and use average basin temperatures and precipitation for the forecast period. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty becomes known and monthly forecasts become more accurate. For more information on the tools we use, consult Water Supply Forecasting Tools.

Volume forecasts represent adjusted flows; that is, observed flows with upstream water use taken into account. Adjusted flows will closely approximate natural or unimpaired flows. However, not all upstream diversions or impoundments are measured or quantifiable. For specific adjustments used with each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through May by the Colorado Basin River Forecast Center. It represents a coordinated effort between the National Weather Service, Natural Resources Conservation Service, Bureau of Reclamation, U.S. Geological Survey and local water district managers.

Note: Data used in this report are provisional and are subject to revision.

For more information, or to be included on the mailing list, please contact:

Colorado Basin River Forecast Center
2242 W North Temple
Salt Lake City, UT 84116
(801) 524-5130
www.cbrfc.noaa.gov