Great Basin 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 Brent.Bernard, Patrick Kormos
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Great Basin Summary






*Median of forecasts within each basin.


Bear Basin Conditions




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

Weber Basin Conditions




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

Six Creeks Basin Conditions




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

Utah Lake Basin Conditions




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


Bear 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
Bear
Utah April-July42 49 54 48 59 67
May-July38 45 50 48 55 63
Woodruff Narrows Rsvr, Abv April-July23 26 32 26 35 40
May-July21 24 30 29 33 38
Montpelier, Nr, Stewart Dam, Blo * April-July19.2 24 32 18 39 47
May-July12 17 25 17 32 40
Smiths Fork
Border, Nr April-July38 45 49 55 54 63
May-July33 40 44 55 49 58
Logan
Logan, Nr, State Dam, Abv April-July42 50 51 46 56 62
May-July35 43 44 46 49 55
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July12.5 15 16 37 16.9 20
May-July8.5 11 12 39 12.9 16.5
Little Bear
Paradise April-July3.5 5 5.4 11 6 8
May-July1 2.5 2.9 9 3.5 5.5

*Regulated Forecast, i.e. Observed flow uncorrected for upstream diversion.

Weber 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
Weber
Oakley, Nr April-July38 46 51 43 57 65
May-July33 41 46 43 52 60
Rockport Res, Wanship, Nr April-July29 37 42 32 50 60
May-July22 30 35 31 43 53
Coalville, Nr April-July27 34 40 30 48 59
May-July19.1 26 32 28 40 51
Chalk Ck
Coalville April-July4 6 7.3 18 8.7 12
May-July2.5 4.5 5.8 17 7.2 10.5
Weber
Echo Reservoir, Echo, At April-July29 38 43 25 54 67
May-July19.7 29 34 24 45 58
Lost Ck
Lost Ck Reservoir, Croyden, Nr April-July2.2 2.5 2.7 20 3.1 4
May-July0.95 1.3 1.5 15 1.9 2.7
East Canyon Ck
East Canyon Reservoir, Morgan, Nr April-July7.5 8.5 9.6 36 11.2 13
May-July4.5 5.5 6.6 35 8.2 10
Weber
Gateway April-July49 58 68 21 87 114
May-July28 37 47 19 66 93
Sf Ogden
Huntsville, Nr April-July9.4 12.5 15 27 19.4 25
May-July5.6 8.7 11.2 28 15.6 21
Ogden
Pineview Reservoir, Ogden, Nr April-July12.6 16 20 18 30 36
May-July5.4 8.8 13 18 23 29


Six Creeks 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
Little Cottonwood Ck
Salt Lake City, Nr April-July16.4 17.9 19.6 52 21 25
May-July15 16.5 18.2 52 20 24
Big Cottonwood Ck
Salt Lake City, Nr April-July11.2 13.6 15.3 43 16.7 20
May-July9 11.4 13.1 41 14.5 18
Mill Ck
Salt Lake City, Nr April-July1.7 2.2 2.4 38 2.6 3.3
May-July1.2 1.7 1.9 35 2.1 2.8
Dell Fk
Little Dell Reservoir April-July1.1 1.5 1.7 31 2.1 2.8
May-July0.8 1.2 1.4 35 1.8 2.5
Lambs Ck
Salt Lake City, Nr April-July0.75 0.99 1.2 22 1.4 2.1
May-July0.6 0.84 1 24 1.3 2
Parleys Ck
Salt Lake City, Nr April-July2.8 3.7 4.4 31 4.5 5.7
May-July2 2.9 3.6 34 4.4 5.6
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July0.21 0.35 0.41 22 0.43 0.48
May-July0.1 0.24 0.3 23 0.32 0.37
City Ck
Salt Lake City, Nr April-July1.8 2.3 2.6 34 2.7 3.1
May-July1.4 1.9 2.2 34 2.3 2.7
S Willow Ck
Grantsville, Nr April-July0.92 1.2 1.4 46 1.5 1.8
May-July0.7 1 1.2 44 1.3 1.5


Utah Lake 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
Spanish Fork
Castilla, Nr April-July9 13 15.1 22 16.5 18.6
May-July6 10 12.1 22 13.5 15.6
Provo
Woodland, Nr April-July34 42 48 48 53 60
May-July30 38 44 49 49 56
Hailstone, Nr April-July35 45 50 45 56 63
May-July30 40 45 46 51 58
Deer Ck Reservoir April-July34 40 49 39 57 64
May-July24 30 39 38 47 54
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July7.5 9 10.4 34 12.1 14.6
May-July6.6 8.1 9.5 34 11.2 13.7
West Canyon Ck
Cedar Fort, Nr April-July0.15 0.21 0.25 14 0.33 0.65
May-July0.15 0.21 0.25 16 0.33 0.65
Salt Ck
Nephi Powerplant Div, Blo April-July1.7 2.1 2.7 33 3 3.5
May-July1.4 1.8 2.4 36 2.7 3.2
Jordan
Utah Lake, Provo, Nr April-July75 84 99 30 110 127
May-July46 55 70 28 81 98

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).

Great Basin 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 Bear
Woodruff Narrows Reservoir, Woodruff, Nr 26.1 58 47 58.3 129 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 952.1 124 73 1076.9 140 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 14.6 103 96 14.2 100 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 39.8 99 72 49.7 124 40.1 55.2
Echo Reservoir, Echo, At 33.3 61 45 65.2 120 54.3 73.9
untitled Lost Ck
Lost Ck Reservoir, Croyden, Nr 16.0 120 71 20.3 152 13.3 22.5
untitled East Canyon Ck
East Canyon Reservoir, Morgan, Nr 36.9 93 75 45.4 115 39.5 49.5
untitled Sf Ogden
Causey Reservoir 5.9 117 83 5.5 110 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 64.6 81 59 92.5 116 79.7 110.1
untitled Provo
Jordanelle Reservoir 211.3 84 66 272.5 108 251.3 320.3
Deer Ck Reservoir 131.7 107 88 135.3 110 123.5 149.7
untitled Dell Fk
Little Dell Reservoir 11.6 -99 56 14.7 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 663.9 80 76 856.9 104 827.8 870.9
untitled
TOTAL 2196.1 97 72 2692.7 119 2264.6 3052.8

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


Hydrologist: Brent.Bernard, Patrick Kormos