Great Basin Water Supply Outlook, May 1, 2020

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-July84 98 105 94 114 124
May-July78 92 99 95 108 118
Woodruff Narrows Rsvr, Abv April-July68 80 89 74 100 112
May-July57 69 78 74 89 101
Montpelier, Nr, Stewart Dam, Blo * April-July131 158 165 91 180 205
May-July95 122 129 89 144 170
Smiths Fork
Border, Nr April-July76 85 87 98 94 103
May-July68 77 79 99 86 95
Logan
Logan, Nr, State Dam, Abv April-July88 102 106 95 113 126
May-July75 89 93 97 100 113
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July30 36 38 88 41 45
May-July20 26 28 90 31 35
Little Bear
Paradise April-July18.1 24 26 55 30 37
May-July8 14.3 16 50 20 27

*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-July72 85 92 78 99 114
May-July63 76 83 78 90 105
Rockport Res, Wanship, Nr April-July66 82 92 70 99 115
May-July55 71 81 72 88 104
Coalville, Nr April-July68 84 94 70 101 118
May-July54 70 80 71 87 104
Chalk Ck
Coalville April-July12.1 16.5 19.6 48 24 32
May-July8 12.4 15.5 46 20 28
Weber
Echo Reservoir, Echo, At April-July79 98 109 64 123 142
May-July62 81 92 64 106 125
Lost Ck
Lost Ck Reservoir, Croyden, Nr April-July6 8.2 9 67 10.2 11.9
May-July3.3 5.5 6.3 66 7.5 9.2
East Canyon Ck
East Canyon Reservoir, Morgan, Nr April-July15.4 18.4 19.8 73 22 27
May-July9 12 13.4 71 16.1 21
Weber
Gateway April-July150 188 199 61 240 275
May-July100 138 149 61 190 225
Sf Ogden
Huntsville, Nr April-July37 40 43 77 54 64
May-July24 27 30 75 41 51
Ogden
Pineview Reservoir, Ogden, Nr April-July60 72 77 68 94 105
May-July33 45 50 68 67 78


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-July29 31 34 89 36 40
May-July27 29 32 91 34 38
Big Cottonwood Ck
Salt Lake City, Nr April-July22 25 27 75 30 34
May-July19 22 24 75 27 31
Mill Ck
Salt Lake City, Nr April-July3.3 4 4.2 66 4.6 5.6
May-July2.5 3.2 3.4 63 3.8 4.8
Dell Fk
Little Dell Reservoir April-July3.2 3.7 4 73 4.6 5.4
May-July2 2.5 2.8 72 3.4 4.2
Lambs Ck
Salt Lake City, Nr April-July2.3 3 3.2 60 3.8 4.9
May-July1.6 2.3 2.5 60 3.1 4.2
Parleys Ck
Salt Lake City, Nr April-July7.5 8.5 9 63 10.5 12.7
May-July5 6 6.5 61 8 10.2
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July0.67 0.86 0.92 48 1.1 1.4
May-July0.4 0.59 0.65 49 0.84 1.1
City Ck
Salt Lake City, Nr April-July3.6 4.5 4.8 62 5.2 6
May-July3 3.9 4.2 65 4.6 5.4
S Willow Ck
Grantsville, Nr April-July1.5 1.8 1.9 60 2.2 2.6
May-July1.3 1.5 1.6 60 1.9 2.4


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-July23 28 30 43 32 38
May-July15 19.5 22 41 24 30
Provo
Woodland, Nr April-July74 83 90 90 98 109
May-July65 74 81 91 89 100
Hailstone, Nr April-July78 88 95 86 104 111
May-July69 79 86 89 95 102
Deer Ck Reservoir April-July80 94 102 80 113 125
May-July65 79 87 84 98 110
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July15 17.5 18.8 61 21 26
May-July13.5 16 17.3 62 19.7 25
West Canyon Ck
Cedar Fort, Nr April-July0.4 0.64 0.84 48 1.2 1.5
May-July0.3 0.54 0.74 48 1.1 1.4
Salt Ck
Nephi Powerplant Div, Blo April-July2.4 3.6 3.9 47 4.2 5.2
May-July2 3.2 3.5 53 3.8 4.8
Jordan
Utah Lake, Provo, Nr April-July163 185 198 61 225 255
May-July105 127 140 56 165 195

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 58.3 129 104 57.9 129 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 1076.9 140 83 1036.2 134 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 14.2 100 93 13.0 92 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 49.7 124 90 41.5 103 40.1 55.2
Echo Reservoir, Echo, At 65.2 120 88 50.1 92 54.3 73.9
untitled Lost Ck
Lost Ck Reservoir, Croyden, Nr 20.3 152 90 21.5 161 13.3 22.5
untitled East Canyon Ck
East Canyon Reservoir, Morgan, Nr 45.4 115 92 42.1 107 39.5 49.5
untitled Sf Ogden
Causey Reservoir 5.5 110 78 6.6 132 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 92.5 116 84 80.0 100 79.7 110.1
untitled Provo
Jordanelle Reservoir 272.5 108 85 219.4 87 251.3 320.3
Deer Ck Reservoir 135.3 110 90 145.6 118 123.5 149.7
untitled Dell Fk
Little Dell Reservoir 14.7 -99 72 14.6 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 856.9 104 98 639.3 77 827.8 870.9
untitled
TOTAL 2692.7 119 89 2353.1 104 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