Great Basin Water Supply Outlook, April 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-July97 108 113 101 128 147
Woodruff Narrows Rsvr, Abv April-July89 96 107 88 123 159
Montpelier, Nr, Stewart Dam, Blo * April-July165 180 190 104 240 300
Smiths Fork
Border, Nr April-July79 84 91 102 101 111
Logan
Logan, Nr, State Dam, Abv April-July92 96 107 96 116 134
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July37 40 42 98 49 65
Little Bear
Paradise April-July30 35 38 81 51 63

*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-July82 91 97 82 112 137
Rockport Res, Wanship, Nr April-July84 97 103 78 123 157
Coalville, Nr April-July86 99 104 78 127 164
Chalk Ck
Coalville April-July15 17.7 22 54 31 49
Weber
Echo Reservoir, Echo, At April-July99 116 125 73 156 210
Lost Ck
Lost Ck Reservoir, Croyden, Nr April-July8 10 10.6 79 12.1 15.8
East Canyon Ck
East Canyon Reservoir, Morgan, Nr April-July22 25 28 104 36 45
Weber
Gateway April-July185 215 235 72 295 380
Sf Ogden
Huntsville, Nr April-July49 54 57 102 68 89
Ogden
Pineview Reservoir, Ogden, Nr April-July88 101 110 97 131 173


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-July33 34 37 97 41 45
Big Cottonwood Ck
Salt Lake City, Nr April-July30 32 35 97 39 45
Mill Ck
Salt Lake City, Nr April-July4.9 5.6 6 94 6.5 7.8
Dell Fk
Little Dell Reservoir April-July4.4 5 5.5 100 6.3 8.2
Lambs Ck
Salt Lake City, Nr April-July3.7 4.5 5.1 96 5.9 7.3
Parleys Ck
Salt Lake City, Nr April-July10.5 12.1 13.5 95 15.9 20
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July1.1 1.3 1.5 78 1.9 2.2
City Ck
Salt Lake City, Nr April-July5.4 5.8 6.3 82 7.4 8.4
S Willow Ck
Grantsville, Nr April-July0 0 2.4 77 0 0


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-July30 33 35 51 39 49
Provo
Woodland, Nr April-July83 93 100 100 108 129
Hailstone, Nr April-July90 102 110 100 117 141
Deer Ck Reservoir April-July100 113 121 95 132 164
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July18.9 20 23 74 26 30
West Canyon Ck
Cedar Fort, Nr April-July0.56 0.95 1.1 62 1.5 2.3
Salt Ck
Nephi Powerplant Div, Blo April-July3.4 3.9 4.6 55 5.5 7
Jordan
Utah Lake, Provo, Nr April-July194 215 225 69 270 325

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 57.8 151 104 25.2 66 38.2 55.8
untitled Bear River
Bear Lake, Nr Lifton 1031.4 141 79 970.0 133 731.1 1302.0
untitled Little Bear
Hyrum Reservoir 11.8 90 77 10.2 79 13.0 15.3
untitled Weber
Rockport Res, Wanship, Nr 47.5 126 86 36.4 97 37.6 55.2
Echo Reservoir, Echo, At 60.2 120 81 31.9 64 50.2 73.9
untitled Lost Ck
Lost Ck Reservoir, Croyden, Nr 18.1 162 80 15.3 137 11.2 22.5
untitled East Canyon Ck
East Canyon Reservoir, Morgan, Nr 44.8 126 91 33.1 93 35.5 49.5
untitled Sf Ogden
Causey Reservoir 5.6 175 80 3.3 102 3.2 7.1
untitled Ogden
Pineview Res, Ogden, Nr 71.5 114 65 70.3 112 62.7 110.1
untitled Provo
Jordanelle Reservoir 266.4 110 83 194.1 80 242.0 320.3
Deer Ck Reservoir 142.7 120 95 131.9 110 119.4 149.7
untitled Dell Fk
Little Dell Reservoir 15.0 -99 73 14.2 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 854.1 105 98 588.9 72 812.8 870.9
untitled
TOTAL 2612.0 121 86 2110.6 98 2157.1 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