Great Basin Water Supply Outlook, May 1, 2018

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-July69 80 87 78 92 105
May-July59 70 77 74 82 95
Woodruff Narrows Rsvr, Abv April-July47 57 67 55 72 98
May-July36 46 56 53 61 87
Montpelier, Nr, Stewart Dam, Blo * April-July40 58 63 35 77 113
May-July14 32 37 26 51 87
Smiths Fork
Border, Nr April-July65 74 78 88 83 91
May-July53 62 66 83 71 79
Logan
Logan, Nr, State Dam, Abv April-July88 98 104 94 107 121
May-July73 83 89 93 92 106
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July26 30 31 72 33 39
May-July16.4 20 21 68 23 29
Little Bear
Paradise April-July21 26 28 60 31 37
May-July6.9 11.9 14.2 44 17.4 23

*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-July45 56 61 52 67 80
May-July37 48 53 50 59 72
Rockport Res, Wanship, Nr April-July38 47 53 40 58 75
May-July29 38 44 39 49 66
Coalville, Nr April-July35 44 51 38 56 76
May-July25 34 41 36 46 66
Chalk Ck
Coalville April-July10 13 15.7 38 18 28
May-July6 9 11.7 34 14 24
Weber
Echo Res, Echo, At April-July41 55 67 39 75 101
May-July27 41 53 37 61 87
Lost Ck
Lost Ck Res, Croydon, Nr April-July3.8 4.8 5.2 39 5.8 8
May-July1.6 2.7 3.1 32 3.7 5.9
East Canyon Ck
East Canyon Res, Morgan, Nr April-July7 8.5 9.7 36 10.8 15
May-July3.2 4.7 5.9 31 7 11.2
Weber
Gateway April-July65 89 103 32 115 180
May-July30 54 68 28 80 145
Sf Ogden
Huntsville, Nr April-July26 32 34 61 38 50
May-July14.1 20 22 55 26 38
Ogden
Pineview Res, Ogden, Nr April-July32 40 45 40 54 68
May-July15.3 24 29 40 38 52


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-July18.6 21 23 61 26 29
May-July16 18 20 57 23 26
Big Cottonwood Ck
Salt Lake City, Nr April-July14.9 16.9 18.7 52 22 26
May-July12 14 15.8 49 18.7 23
Mill Ck
Salt Lake City, Nr April-July2.1 2.4 2.7 42 3.1 3.4
May-July1.4 1.7 2 37 2.4 2.7
Dell Fk
Little Dell Res April-July1.2 1.5 1.8 32 2.2 3
May-July0.8 1.1 1.4 35 1.8 2.6
Lambs Ck
Salt Lake City, Nr April-July1 1.4 1.6 30 2 3.1
May-July0.55 0.95 1.1 27 1.5 2.6
Parleys Ck
Salt Lake City, Nr April-July3.2 3.9 4.5 32 5.4 6.9
May-July1.8 2.5 3.1 29 4 5.5
Emigration Ck
Salt Lake City, Nr April-July0.46 0.59 0.82 21 1.1 1.5
May-July0.12 0.25 0.48 17.8 0.75 1.2
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July0.2 0.29 0.38 20 0.49 0.59
May-July0.06 0.15 0.24 0 0.35 0.45
City Ck
Salt Lake City, Nr April-July2.6 3 3.5 45 4.2 4.9
May-July2 2.4 2.9 45 3.6 4.3
S Willow Ck
Grantsville, Nr April-July1.1 1.3 1.4 45 1.6 1.9
May-July0.8 1 1.2 43 1.3 1.6


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 11 13.5 19.6 15.5 19
May-July5 7 9.5 17.6 11.5 15
Provo
Woodland, Nr April-July49 57 61 61 67 80
May-July37 45 49 55 55 68
Hailstone, Nr April-July54 61 66 60 71 84
May-July42 49 54 56 59 72
Deer Ck Res April-July51 59 64 50 71 85
May-July36 44 49 47 56 70
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July7.5 9 10.4 34 13.5 15.5
May-July6 7.5 8.9 32 12 14
West Canyon Ck
Cedar Fort, Nr April-July0.11 0.17 0.23 13.1 0.36 0.51
May-July0.1 0.16 0.22 14.3 0.35 0.5
Salt Ck
Nephi Powerplant Div, Blo April-July2.5 2.9 3.3 40 3.7 4.7
May-July2.1 2.5 2.9 44 3.3 4.3
Jordan
Utah Lake, Provo, Nr April-July103 120 137 42 152 170
May-July40 57 74 30 89 107

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 Res, Woodruff, Nr 59.0 131 106 50.4 112 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 1147.5 149 88 1002.3 130 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 13.8 97 90 10.4 73 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 55.8 139 101 26.9 67 40.1 55.2
Echo Res, Echo, At 72.3 133 98 49.4 91 54.3 73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr 21.4 161 95 18.5 139 13.3 22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr 47.6 121 96 43.5 110 39.5 49.5
untitled Sf Ogden
Causey Res 7.1 141 101 7.1 142 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 105.3 132 96 74.6 94 79.7 110.1
untitled Jordanelle Dam
265.6 106 83 254.9 101 251.3 320.3
untitled Provo
Deer Ck Res 148.1 120 99 146.6 119 123.5 149.7
untitled Dell Fk
Little Dell Res 16.1 -99 78 13.6 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 648.9 78 75 575.1 69 827.8 870.9
untitled
TOTAL 2592.5 114 85 2259.6 100 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