Lake Powell Water Supply Outlook, April 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-July125 150 175 71 198 225
Pine Ck
Fremont Lk, Abv April-July45 57 67 68 75 82
New Fork
Big Piney, Nr April-July95 131 170 48 220 265
Green
Fontenelle Reservoir, Fontenelle, Nr April-July240 320 430 59 505 580
Big Sandy
Farson, Nr April-July16 22 27 52 35 43
Green
Green River, Wy, Nr April-July235 310 420 58 500 605
Hams Fork
Frontier, Nr, Pole Ck, Blo April-July22 27 31 57 40 50
Viva Naughton Reservoir April-July28 34 40 54 52 70
Blacks Fork
Robertson, Nr April-July36 44 50 56 61 78
Ef Smiths Fork
Stateline Reservoir, Robertson,nr April-July13 16 19 73 21 25
Green
Flaming Gorge Reservoir April-July330 410 530 54 680 910


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 11 13.5 59 16 19
Steamboat Springs April-July97 119 143 55 173 215
Elk
Milner, Nr April-July154 187 215 67 250 295
Elkhead Ck
Long Gulch, Abv, Hayden, Nr April-July18 28 34 47 44 55
Yampa
Maybell, Nr April-July365 470 550 59 650 765
Little Snake
Slater, Nr April-July69 91 110 71 128 150
Dixon, Nr April-July130 170 205 59 260 325
Lily, Nr April-July120 168 205 59 260 340
Yampa
Deerlodge Park April-July475 650 775 63 920 1120
White
Meeker, Nr April-July126 145 160 57 183 225
Watson, Nr April-July130 148 161 58 188 235


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-July7.6 9.2 11.9 57 12.7 19.1
Ashley Ck
Vernal, Nr April-July15.6 19.3 23 46 25 40
West Fork Duchesne
Vat Diversion, Blo April-July4.6 5.9 7.4 40 7.9 10.9
Duchesne
Tabiona, Nr April-July42 49 57 53 62 73
Rock Ck
Upper Stillwater Reservoir April-July27 35 40 54 45 56
South Fork Rock Ck
Docs Div, Blo April-July1.9 2.8 3.3 45 3.8 4.9
Rock Ck
Mountain Home, Nr April-July33 42 49 56 53 66
Currant Ck
Currant Ck Reservoir April-July4.3 5.5 6.7 34 9.9 12
Strawberry
Strawberry Reservoir, Soldier Springs April-July10 14.6 18.8 26 21 31
Starvation Reservoir, Duchesne, Nr April-July29 37 40 36 49 58
Duchesne
Duchesne, Nr, Knight Div, Abv April-July76 92 104 54 114 137
Lake Fork
Moon Lake Reservoir, Mtn Home, Nr April-July19 29 33 50 36 47
Yellowstone
Altonah, Nr April-July21 28 33 54 36 47
Whiterocks
Whiterocks, Nr April-July14 21 25 46 27 37
Uinta
Neola, Nr April-July18.5 28 35 47 39 56
Duchesne
Myton April-July55 84 110 33 122 174
Randlett, Nr April-July65 94 116 30 132 186


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-July1.7 3.1 4.3 28 4.8 6.9
Fish Ck
Scofield, Nr, Reservoir, Abv April-July9.3 11.6 13.9 46 15 19.9
Price
Scofield Reservoir, Scofield, Nr April-July11.9 14.7 17.6 43 18.9 26
Green
Green River, Ut April-July970 1250 1500 51 1890 2450
Huntington Ck
Electric Lake April-July4 4.5 5.1 38 5.7 7.9
Power Plant, Blo April-July18 19.1 20 50 21 28
Seeley Ck
Joes Vly Reservoir, Orangeville, Nr April-July16.8 19.6 24 43 27 38
Ferron Ck
Ferron, Nr April-July9.7 13.6 18.1 48 21 29
Muddy Ck
Emery, Nr April-July5.1 6.1 7.4 37 8.2 11


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-July115 140 165 75 195 225
Willow Ck
Willow Ck Reservoir, Granby, Nr April-July16 23 30 64 38 46
Fraser
Winter Park April-July12 14 15.5 80 17 20
Williams Fork
Williams Fork Reservoir, Parshall April-July47 55 63 66 74 85
Muddy Ck
Wolford Mountain Reservoir April-July18 24 30 56 37 44
Blue
Dillon Reservoir April-July75 92 108 66 125 145
Green Mtn Reservoir April-July125 150 180 65 205 235
Colorado
Kremmling, Nr April-July420 500 580 67 690 800
Eagle
Gypsum, Blo April-July140 170 200 60 240 280
Colorado
Dotsero, Nr April-July640 780 910 65 1090 1280
Frying Pan
Ruedi Reservoir, Basalt, Nr April-July70 85 100 72 115 135
Roaring Fork
Glenwood Springs April-July360 420 470 68 540 610
Colorado
Glenwood Springs, Blo April-July1000 1200 1400 66 1650 1940
Cameo, Nr April-July1100 1300 1500 64 1800 2100
Plateau Ck
Cameo, Nr April-July24 35 46 37 66 86
Colorado
Cisco, Nr April-July1800 2200 2550 57 3000 3500
Lake Powell, Glen Cyn Dam, At April-July1700 2600 3200 45 4000 5400


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-July56 63 70 71 80 90
Almont April-July85 95 105 68 120 140
East
Almont April-July95 110 125 69 145 165
Gunnison
Gunnison, Nr April-July185 215 240 65 285 335
Tomichi Ck
Gunnison April-July25 34 43 58 54 65
Lake Fork
Gateview April-July60 73 86 70 105 125
Gunnison
Blue Mesa Reservoir April-July330 385 440 65 530 630
Morrow Point Reservoir April-July360 420 480 65 580 680
Crystal Reservoir April-July400 470 540 65 650 760
Muddy Ck
Paonia Reservoir, Bardine, Nr March-June24 34 42 44 53 62
April-June23 33 41 45 52 61
April-July24 34 42 43 53 62
Nf Gunnison
Somerset, Nr April-July105 135 160 54 185 215
Surface Ck
Cedaredge April-July4 5.5 7 42 9 11
Uncompahgre
Ridgway Reservoir April-July42 52 62 61 74 86
Colona April-July46 60 74 54 94 114
Delta April-July22 34 46 41 65 84
Gunnison
Grand Junction, Nr April-July600 730 860 58 1040 1230


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-July80 99 118 48 153 186
Mcphee Reservoir April-July83 105 130 44 165 205
San Miguel
Placerville, Nr April-July47 58 67 52 83 100
Dolores
Cisco, Nr April-July145 185 225 40 295 375


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-July106 120 135 63 156 185
Carracas, Nr April-July185 210 235 62 275 315
Navajo Reservoir, Archuleta, Nr April-July270 325 395 54 460 565
Farmington April-July370 445 520 47 645 790
Bluff, Nr April-July330 400 505 46 630 780
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July32 36 41 76 46 53
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July35 40 47 72 53 60
Little Navajo
Oso Div Dam,bl,chromo,nr April-July2.9 3.6 4.3 57 5.1 6
Piedra
Arboles, Nr April-July70 84 105 50 126 165
Los Pinos
Vallecito Reservoir, Bayfield, Nr April-July68 86 103 53 125 153
Animas
Durango April-July140 178 210 51 255 310
Florida
Lemon Reservoir, Durango, Nr April-July16 21 26 47 32 39
La Plata
Hesperus April-July5 6.5 8.5 37 10.9 14.5
Mancos
Mancos, Nr April-July6.4 8.4 10.8 35 13.8 18

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 120.9 99 36 135.8 112 121.7 334.0
untitled Big Sandy
Big Sandy Reservoir, Nr Farson 9.2 47 24 24.5 125 19.6 38.3
Blacks Fork
Meeks Cabin 6.0 44 20 12.1 90 13.4 29.9
untitled Ef Smiths Fork
Stateline Reservoir, Robertson,nr 4.0 72 29 5.8 106 5.5 13.9
untitled Green
Flaming Gorge Reservoir 3168.0 105 85 3220.1 107 3021.3 3749.0
untitled Strawberry
Strawberry Reservoir, Soldier Springs 927.6 140 84 978.4 147 663.7 1105.9
Starvation Reservoir, Duchesne, Nr 161.3 108 98 164.7 110 149.7 165.3
untitled Rock Ck
Upper Stillwater Reservoir 2.0 45 6 6.7 150 4.5 31.4
untitled Lake Fork
Moon Lake Reservoir, Mtn Home, Nr 14.2 52 39 29.5 108 27.3 36.5
untitled Big Brush Ck
Red Fleet Reservoir, Vernal, Nr 16.6 87 65 22.0 115 19.0 25.7
untitled Price
Scofield Reservoir, Scofield, Nr 36.1 117 55 52.2 169 30.9 65.8
untitled Seeley Ck
Joes Vly Reservoir, Orangeville, Nr 38.5 96 62 48.5 121 40.0 62.5
untitled Huntington Ck
Electric Lake 18.6 102 59 22.7 124 18.3 31.5
untitled
TOTAL 4522.9 109 79 4723.1 114 4134.9 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 355.3 113 72 397.3 126 314.3 490.3
untitled Willow Ck
Willow Ck Reservoir, Granby, Nr 7.8 95 85 9.6 117 8.2 9.1
untitled Williams Fork
Williams Fork Reservoir, Parshall 64.7 106 67 74.4 122 60.8 96.9
untitled Muddy Ck
Wolford Mountain Reservoir 52.9 121 80 50.8 116 43.7 66.0
untitled Blue
Dillon Reservoir 199.3 92 78 228.1 106 215.5 254.0
Green Mtn Reservoir 66.8 101 45 69.2 105 65.9 146.9
untitled Homestake Ck
Homestake Reservoir 11.8 47 27 41.0 163 25.1 43.0
untitled Frying Pan
Ruedi Reservoir, Basalt, Nr 58.4 92 57 68.2 108 63.2 102.0
untitled Plateau Ck
Vega Reservoir, Collbran, Nr 6.1 43 19 16.0 113 14.2 32.9
untitled Taylor
Taylor Park Reservoir 62.1 99 58 71.2 114 62.4 106.2
untitled Gunnison
Blue Mesa Reservoir 399.0 88 48 534.4 117 454.9 827.9
Morrow Point Reservoir 104.9 94 90 105.7 95 111.7 117.0
Crystal Reservoir 15.7 97 90 17.4 107 16.2 17.5
untitled Muddy Ck
Paonia Reservoir, Bardine, Nr 5.4 174 32 7.8 252 3.1 16.7
untitled Uncompahgre
Ridgway Reservoir 55.2 79 67 67.0 96 70.0 83.0
untitled Dolores
Mcphee Reservoir 169.4 59 44 280.5 98 285.4 381.1
untitled
TOTAL 1634.6 90 59 2038.4 112 1814.5 2790.6
Colorado
Lake Powell 8843.8 52 36 11822.0 70 16941.7 24322.0
untitled
TOTAL 8843.8 52 36 11822.0 70 16941.7 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 44.3 70 35 83.5 132 63.2 125.4
untitled San Juan
Navajo Reservoir, Archuleta, Nr 1042.2 80 61 1292.5 99 1310.4 1696.0
untitled Florida
Lemon Reservoir, Durango, Nr 11.1 51 28 17.7 82 21.7 39.8
untitled
TOTAL 1097.6 79 59 1393.7 100 1395.3 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