Great Salt Lake Water Supply Outlook, May 1, 2015

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by W. P. Miller
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Great Salt Lake 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
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Bear
Utah April-July53 61 54 70
May-July43 51 49 60
Woodruff Narrows Rsvr, Abv April-July32 36 30 45
May-July27 31 30 40
Montpelier, Nr, Stewart Dam, Blo * April-July51 58 32 80
May-July42 49 34 71
Smiths Fork
Border, Nr April-July63 70 79 78
May-July50 57 71 65
Logan
Logan, Nr, State Dam, Abv April-July48 54 49 62
May-July40 46 48 54
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July13.4 14.3 33 17.5
May-July9.6 10.5 34 13.7
Little Bear
Paradise April-July7.8 8.3 17.7 10.2
May-July5.4 5.9 18.4 7.8

*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
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Weber
Oakley, Nr April-July46 54 46 67
May-July36 44 42 57
Rockport Res, Wanship, Nr April-July30 38 29 54
May-July24 32 28 48
Coalville, Nr April-July29 36 27 52
May-July21 28 25 44
Chalk Ck
Coalville April-July7.5 9.8 24 14.3
May-July5.1 7.4 22 11.9
Weber
Echo Res, Echo, At April-July35 44 26 64
May-July24 33 23 53
Lost Ck
Lost Ck Res, Croydon, Nr April-July2.5 2.5 18.7 2.9
May-July1.3 1.3 13.4 1.7
East Canyon Ck
East Canyon Res, Morgan, Nr April-July6 6.2 23 8
May-July4.1 4.3 23 6.1
Weber
Gateway April-July48 58 17.8 92
May-July29 39 15.9 73
Sf Ogden
Huntsville, Nr April-July12.9 13.8 25 18.6
May-July7.6 8.5 21 13.3
Ogden
Pineview Res, Ogden, Nr April-July16.2 18.1 16 27
May-July8.3 10.2 14 19


Six Creeks Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Little Cottonwood Ck
Salt Lake City, Nr April-July16.7 18 47 23
May-July14.6 15.9 45 21
Big Cottonwood Ck
Salt Lake City, Nr April-July10.1 11.5 32 15.3
May-July8.2 9.6 30 13.4
Mill Ck
Salt Lake City, Nr April-July1.2 1.3 19.8 1.7
May-July0.84 0.91 16.9 1.3
Dell Fk
Little Dell Res April-July0.62 0.68 12.4 1.2
May-July0.35 0.41 10.5 0.89
Parleys Ck
Salt Lake City, Nr April-July1.8 1.9 13.7 2.7
May-July1.2 1.4 12.7 2.1
Emigration Ck
Salt Lake City, Nr April-July0.46 0.46 11.5 0.73
May-July0.4 0.4 14.8 0.67
City Ck
Salt Lake City, Nr April-July2.1 2.4 31 3.1
May-July1.7 1.9 29 2.6
S Willow Ck
Grantsville, Nr April-July0.99 1.1 37 1.6
May-July0.76 0.91 34 1.3


Utah Lake Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period
90%
Exceedance
Volume
50%
Exceedance
Volume
Percent
Average
10%
Exceedance
Volume
Spanish Fork
Castilla, Nr April-July12.4 13.4 19.4 16.1
May-July8.4 9.4 17.4 12.1
Provo
Woodland, Nr April-July48 55 55 64
May-July36 43 48 52
Hailstone, Nr April-July53 60 55 70
May-July40 47 48 57
Deer Ck Res April-July46 52 41 63
May-July33 39 38 50
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July6.4 7.5 24 11
May-July4.9 6 21 9.5
West Canyon Ck
Cedar Fort, Nr April-July0.09 0.1 5.7 0.19
May-July0.08 0.09 5.8 0.18
Jordan
Utah Lake, Provo, Nr April-July81 93 29 118
May-July42 54 22 79

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 Salt Lake 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 Res, Woodruff, Nr 54.6 121 98 38.1 85 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 716.7 93 55 728.7 95 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 14.7 104 96 14.5 102 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 44.9 112 81 36.1 90 40.1 55.2
Echo Res, Echo, At 46.3 85 63 43.0 79 54.3 73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr 15.0 113 67 14.7 110 13.3 22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr 31.6 80 64 30.7 78 39.5 49.5
untitled Sf Ogden
Causey Res 7.1 142 101 5.9 117 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 77.2 97 70 83.0 104 79.7 110.1
untitled Jordanelle Dam
215.0 86 67 173.1 69 251.3 320.3
untitled Provo
Deer Ck Res 145.3 118 97 133.6 108 123.5 149.7
untitled Dell Fk
Little Dell Res 12.8 -99 62 13.3 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr -9999.0 -99 -99 684.3 83 827.8 870.9
untitled
TOTAL 1368.4 95 63 1985.7 88 1436.7 2181.9

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: W. P. Miller