Note: This publication is currently undergoing major revisions. The current publication will be replaced with a new publication based on stakeholder requirements and scientific advances. We expect to begin sharing details on this soon. If you have input on content, format, or publication frequency at any time, please contact us at cbrfc.webmasters@noaa.gov.Lake Powell Water Supply Outlook, April 1, 2011

Lake Powell Water Supply Outlook, April 1, 2011


Prepared by Alcorn
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

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 125 percent of average in the Upper Green basin. March precipitation was 105 percent of average in the basin as a whole; however, portions of the basin received much above average precipitation such as the headwaters of the mainstem of the Green River which received near 150 percent of average.

Snow:
April 1st snow water equivalent was 120 percent of average in the basin.
--- Upper Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 80 percent of average.

Soil Moisture:
Modeled soil moisture states were below average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between La Nina conditions and winter precipitation in the Upper Green basin.

Forecast Summary:
With the addition of another month of near average precipitation and localized areas with much above average precipitation, the seasonal precipitation and snow water equivalent still remain above average for the Upper Green. As a result of the current conditions, the April through July streamflow volume forecasts increased by approximately 5 to 10 percent from the March 1 forecasts. Current forecasts range between 100 and 140 percent of average with a median value of 114 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Yampa/White Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 130 percent of average in the Yampa/White basin. March precipitation was 120 percent of average in the basin as a whole.

Snow:
April 1st snow water equivalent was 130 percent of average in the basin.
--- Yampa basin snow water equivalent plot.

Streamflow:
March streamflow was near 100 percent of average.

Soil Moisture:
Modeled soil moisture states were near average heading into the winter for the Yampa, Little Snake,and White River basins.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Yampa/White basin.

Forecast Summary:
With the addition of above average precipitation in March, the seasonal precipitation and current snow water equivalent remain much above average. It is also important to note that many of the snotel locations have record or near record snow water equivlent for this time of the year. As a result of the current conditions, the April through July streamflow volume forecasts have increased by approximately 10 to 20 percent. Current forecasts range between 128 and 162 percent of average with a median value of 151 percent. Many of these forecast volumes are in the top five historical observed volumes.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Duchesne Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 155 percent of average in the Duchesne basin. March precipitation was 85 percent of average the basin as a whole; however, portions of the basin received much below average precipitation such as the headwaters of Ashley Creek, Big Brush, and Whiterocks.

Snow:
April 1st snow water equivalent was 145 percent of average in the basin.
--- Duchesne basin snow water equivalent plot.

Streamflow:
March streamflow was 90 percent of average.

Soil Moisture:
Modeled soil moisture states were much below average to below average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Duchesne basin.

Forecast Summary:
Seasonal precipitation and current snow water equivalent still remain much above average in spite of the below average March precipitation. As a result of the current conditions, the majority of the April through July streamflow volume forecasts did not change from March. However, forecasts for the Duchesne, Strawberry, and Rock Creek rivers have increased by approximately 5 to 10 percent while forecasts for Ashley Creek, Big Brush, and Whiterocks have decreased by approximately 5 to 10 percent as a result of the much below average March precipitation. Current forecasts range between 106 and 193 percent of average with a median value of 153 percent. Many of these forecast volumes are in the top five historical observed volumes.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Lower Green Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 160 percent of average in the Lower Green basin. March precipitation was 90 percent of average.

Snow:
April 1st snow water equivalent was 120 percent of average in the basin as a whole.
--- Lower Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 80 percent of average.

Soil Moisture:
Modeled soil moisture states were much below to near average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Lower Green basin.

Forecast Summary:
With the addition of near average precipitation in March, the seasonal precipitation and current snow water equivalent remain much above average and above average, respectively. As a result of the current conditions, the April through July streamflow volume forecasts are similar to the March forecasts with the exception of Green River at Green River, UT which increase by 11 percent. Current forecasts range between 121 and 151 percent of average with a median value of 141 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Upper Colorado Mainstem Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation remains much above average in the Upper Colorado mainstem basin at 130 percent of average. March precipitation was near 125 percent of average in the basin as a whole. However, the uppermost headwaters of the basin received near 150% of average precipitation for the month.

Snow:
April 1st snow water equivalent was near 130 percent of average in the basin as a whole. This is significant for this time of year as it is also near 130% of the average seasonal peak. Many snotel sites in the upper portion of the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
March streamflow was near 100 percent of average.

Soil Moisture:
Modeled soil moisture states were near to above average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between La Nina conditions and winter precipitation in the Upper Colorado mainstem basin.

Forecast Summary:
Almost all forecast volumes were raised from last month due to yet another month of above average precipitation combined with the much above average snow water equivalent at this point in the season. Current April through July streamflow volume forecasts range between 120 and 150 percent of average with a median value of 135 percent. Many of these forecast volumes are in the top five of historical volumes observed since 1970.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Gunnison Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 115 percent of average in the Gunnison basin. March precipitation was 90 percent of average.

Snow:
April 1st snow water equivalent was near 115 percent of average in the Gunnison basin; this is around 110% of the seasonal peak.
--- Gunnison basin snow water equivalent plot

Streamflow:
March streamflow was 90 percent of average.

Soil Moisture:
Modeled soil moisture states were below to near average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between La Nina conditions and winter precipitation in the Gunnison basin.

Forecast Summary:
March precipitation throughout the Gunnison basin was average at 90%. Seasonal precipitation for the Gunnison basin dropped a little from last month to 115% of average. April 1st seasonal snow water equivalent for the Gunnison was above average with 115%; whereas the snow water equivalent is 110% of the average seasonal peak. Since there was a slight increases in the seasonal snow water equivalent in the northern portions of the Gunnison basin, the current April through July streamflow volume forecasts remained the same from last month's forecast. Current April through July streamflow volume forecasts range between 83 and 133 percent of average with a median value of 110 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Dolores Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 95 percent of average in the entire Dolores basin. March precipitation was just 60 percent of average.

Snow:
April 1st snow water equivalent was 85 percent of average in the Dolores basin as a whole; this is about 75% of the seasonal peak.
--- Dolores basin snow water equivalent plot

Streamflow:
March streamflow was 60 percent of average.

Soil Moisture:
Modeled soil moisture states were average to slightly below average heading into the winter.

Climate Forecasts:
The correlation of La Nina and April through July water volumes in the Dolores basin is small that it did not influence the forecast process.

Forecast Summary:
March precipitation throughout the Dolores basin was much below average at 60%. Seasonal precipitation for the Dolores basin dropped from last month to 95% of average. April 1st seasonal snow water equivalent for the Dolores was average with 85%; whereas the snow water equivalent is 75% of the average seasonal peak. Since the percent of average for both seasonal snow water equivalent and seasonal precipitation decreased from last month, the current April through July streamflow volume forecasts dropped in the Dolores Basin from last month's forecast. Current April through July streamflow volume forecasts range between 68 and 71 percent of average, with a median value of 70 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

San Juan Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 90 percent of average, which dropped 10 percent from March 1st. March precipitation was 50 percent of average, which was much below average.

Snow:
Current snow water equivalent for the entire basin is 85 percent, which is below average. The Animas basin and above Navajo are similar with 85 percent. All three dropped since March 1st.
--- Animas River Basin Snow Plot.
--- Above Navajo Basin Snow Plot.

Streamflow:
Streamflow for the entire San Juan Basin was much below average for March at 45%. Seasonal streamflow since October continued to be much below average at 60%, due to the much below average fall precipitation.

Soil Moisture:
Modeled soil moisture as of November 1st, 2010 was average to below average across the entire San Juan Basin.

Climate Forecasts:
The correlation of La Nina and April through July water volumes in the San Juan basin does suggest slightly drier than average December through May precipitation, but it did not influence the April forecast process.

Forecast Summary:
Since March precipitation was below to much below average in the San Juan Basin, the April Water Supply April-July volume dropped 10 percent. The April-July forecast were down compared to last month with a range from 70 to 88 percent of average. The median value of 75 percent.



* 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
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Green
Daniel, Nr, Warren Bridge, At April-July245290109340
Pine Ck
Fremont Lk, Abv April-July95111107128
New Fork
Big Piney, Nr April-July325430109550
Green
Fontenelle Res, Fontenelle Nr April-July6909801141250
Big Sandy
Farson, Nr April-July425810077
Green
Green River, Wy, Nr April-July77010201171270
Hams Fork
Frontier, Nr, Pole Ck, Blo April-July6991140116
Viva Naughton Res April-July95125140155
Blacks Fork
Robertson, Nr April-July86115121148
Ef Smiths Fork
Robertson, Nr April-July253612449
Green
Flaming Gorge Res, Flaming Gorge Dam, At April-July97513501131850


Yampa/White Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Yampa
Stagecoach Rsvr, Abv April-July335013565
Steamboat Springs April-July330415148510
Elk
Milner, Nr April-July420500154605
Elkhead Ck
Long Gulch, Abv, Hayden, Nr April-July83115162152
Yampa
Maybell, Nr April-July116015501571990
Little Snake
Slater, Nr April-July184235148290
Dixon, Nr April-July375515156630
Lily, Nr April-July395580159800
White
Meeker, Nr April-July285370128465
Watson, Nr April-July300395130490


Duchesne Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Big Brush Ck
Vernal, Nr, Red Fleet Res, Abv April-July15.32311032
Ashley Ck
Vernal, Nr April-July355510680
West Fork Duchesne
Vat Diversion, Blo April-July253217140
Duchesne
Tabiona, Nr April-July118155148197
Rock Ck
Upper Stillwater Res April-July107125152145
Mountain Home, Nr April-July113135152159
Currant Ck
Currant Ck Res April-July264016057
Strawberry
Soldier Springs, Nr April-July67100169140
Duchesne, Nr April-July136200164275
Duchesne
Duchesne, Nr, Knight Div, Abv April-July230290154360
Lake Fork
Moon Lake Res, Mtn Home, Nr April-July83100147118
Yellowstone
Altonah, Nr April-July7696155118
Whiterocks
Whiterocks, Nr April-July487012596
Uinta
Neola, Nr April-July76112142155
Duchesne
Myton April-July330500189705
Randlett, Nr April-July385625192900


Lower Green Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
White
Blo Tabbyune Ck, Soldier Summit, Nr April-July19.12514432
Fish Ck
Scofield, Nr, Reservoir, Abv April-July334514158
Price
Scofield Res, Scofield, Nr April-July496714689
Green
Green River, Ut April-July329046001456140
Huntington Ck
Electric Lake April-July15.22012725
Huntington, Nr April-July456312984
Seeley Ck
Joes Vly Res, Orangeville, Nr April-July507012194
Ferron Ck
Ferron, Nr April-July395012863
Muddy Ck
Emery, Nr April-July223015140
Seven Mile Ck
Fish Lake, Nr April-July5.9912912.7
Pine Ck
Escalante, Nr April-July1.631254.8


Upper Colorado Mainstem Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Colorado
Lake Granby, Granby, Nr April-July265340151425
Willow Ck
Willow Ck Res, Granby, Nr April-July5575147102
Fraser
Winter Park April-July212613031
Williams Fork
Williams Fork Res, Parshall, Nr April-July103130137160
Muddy Ck
Wolford Mtn Res, Blo April-July6490150120
Blue
Dillon Res April-July176225135280
Green Mtn Res April-July295380136475
Colorado
Kremmling, Nr April-July101012801471580
Eagle
Gypsum, Blo April-July320420125530
Colorado
Dotsero, Nr April-July160020201402570
Frying Pan
Ruedi Res, Basalt, Nr April-July136170121205
Roaring Fork
Glenwood Springs April-July6908501201030
Colorado
Glenwood Springs, Blo April-July235028601323550
Cameo, Nr April-July260032401344020
Plateau Ck
Cameo, Nr April-July100150130200
Colorado
Cisco, Nr April-July430055001187000
Mill Ck
Moab, Nr, Sheley Tun, At April-July3.14.8967
Colorado
Lake Powell, Glen Cyn Dam, At April-July7200950012012300


Gunnison Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Taylor
Taylor Park Res April-July100125121153
Almont April-July160200121240
East
Almont April-July188230120275
Gunnison
Gunnison, Nr April-July380480123595
Tomichi Ck
Gunnison April-July488099125
Lake Fork
Gateview April-July9412196151
Gunnison
Blue Mesa Res April-July635800111985
Morrow Point Res April-July6758751111040
Crystal Res April-July7409851081150
Muddy Ck
Paonia Res, Bardine, Nr March-June99131131168
April-June96126133163
April-July96133130176
Nf Gunnison
Somerset, Nr April-July310380125455
Surface Ck
Cedaredge April-July16.52212929
Uncompahgre
Ridgway Res April-July699593125
Colona April-July8613094183
Delta April-July679783147
Gunnison
Grand Junction, Nr April-July128017001092100


Dolores Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Dolores
Dolores April-July13018771260
Mcphee Res April-July15822570305
San Miguel
Placerville, Nr April-July7011083149
Dolores
Cisco, Nr April-July30042068515


San Juan Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
San Juan
Pagosa Springs April-July13918381225
Carracas, Nr April-July22531077400
Navajo Res, Archuleta, Nr April-July39555070725
Farmington April-July580860711090
Bluff, Nr April-July550850691120
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July31438157
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July39558074
Piedra
Arboles, Nr April-July12117074230
Los Pinos
Vallecito Res, Bayfield, Nr April-July12216078205
Animas
Durango April-July29037585470
Florida
Lemon Res, Durango, Nr April-July31427255
La Plata
Hesperus April-July12.6187225
Mancos
Mancos, Nr April-July11.2247338
South Ck
Lloyds Rsvr Nr Monticello, Abv March-July0.30.78571.6
April-July0.270.71531.5

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).

Reservoir Monthly Inflow Forecasts














Green End of Month Reservoir Contents (kaf)

Usable
Capacity
EOM
Contents
Percent
Usable
Capacity
Last Year
EOM
Last Year
%Capacity
untitled Green
Fontenelle Res, Fontenelle Nr 344.8 135.7 39 112.5 33
Flaming Gorge Res, Flaming Gorge Dam, At 3752.0 3159.8 84 3197.7 85
untitled Strawberry
Strawberry Res 1105.9 974.0 88 974.5 88
Starvation Res, Duchesne, Nr 165.3 130.3 79 162.3 98
untitled Price
Scofield Res, Scofield, Nr 65.8 27.5 42 29.5 45
untitled Seeley Ck
Joes Vly Res, Orangeville, Nr 61.6 42.6 69 43.3 70
untitled Huntington North Reservoir Storage
4.2 4.1 96 3.4 80
untitled
TOTAL 5499.6 4474.0 81 4523.1 82


Upper Colorado End of Month Reservoir Contents (kaf)

Usable
Capacity
EOM
Contents
Percent
Usable
Capacity
Last Year
EOM
Last Year
%Capacity
untitled Colorado
Lake Granby, Granby, Nr 490.3 344.5 70 302.3 62
untitled Willow Ck
Willow Ck Res, Granby, Nr 9.1 7.2 79 7.5 82
untitled Williams Fork
Williams Fork Res, Parshall, Nr 96.9 79.5 82 74.8 77
untitled Muddy Ck
Wolford Mountain Reservoir 66.0 55.4 84 51.7 78
untitled Blue
Dillon Res 254.0 221.8 87 241.2 95
Green Mtn Res 146.9 66.0 45 77.4 53
untitled Homestake Ck
Homestake Res 43.0 23.0 53 21.8 51
untitled Frying Pan
Ruedi Res, Basalt, Nr 102.0 64.8 64 66.3 65
untitled Plateau Ck
Vega Res, Collbran, Nr 32.9 14.1 43 13.3 40
untitled Taylor
Taylor Park Res 106.2 72.9 69 62.7 59
untitled Gunnison
Blue Mesa Res 829.5 495.0 60 542.2 65
Morrow Point Res 117.0 112.5 96 107.0 91
Crystal Res 17.5 16.6 95 16.6 95
untitled Muddy Ck
Paonia Res, Bardine, Nr 18.5 0.9 5 1.6 9
untitled Uncompahgre
Ridgway Res 83.2 64.0 77 67.5 81
untitled Dolores
Mcphee Res 381.1 280.5 74 251.5 66
untitled
TOTAL 2794.1 1918.7 69 1905.2 68
Colorado
Lake Powell 24322.0 12803.9 53 13700.8 56
untitled
TOTAL 24322.0 12803.9 53 13700.8 56


San Juan End of Month Reservoir Contents (kaf)

Usable
Capacity
EOM
Contents
Percent
Usable
Capacity
Last Year
EOM
Last Year
%Capacity
untitled Los Pinos
Vallecito Res, Bayfield, Nr 125.4 76.8 61 42.1 34
untitled San Juan
Navajo Res, Archuleta, Nr 1701.3 1326.1 78 1246.6 73
untitled Florida
Lemon Res, Durango, Nr 39.8 14.7 37 9.4 24
untitled
TOTAL 1866.5 1417.6 76 1298.0 70

Monthly Streamflows

















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