Great Basin Water Supply Outlook, February 1, 2018

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by B.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 85 99 88 113 135
Woodruff Narrows Rsvr, Abv April-July55 72 86 71 107 146
Montpelier, Nr, Stewart Dam, Blo * April-July43 62 83 46 143 220
Smiths Fork
Border, Nr April-July40 57 73 82 86 104
Logan
Logan, Nr, State Dam, Abv April-July71 86 98 88 106 135
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July25 28 32 74 37 49
Little Bear
Paradise April-July10.3 15.6 21 45 30 42

*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-July49 60 76 64 90 112
Rockport Res, Wanship, Nr April-July40 54 67 51 88 117
Coalville, Nr April-July37 52 66 49 87 117
Chalk Ck
Coalville April-July10.4 14.3 18.1 44 26 38
Weber
Echo Res, Echo, At April-July46 65 85 50 111 154
Lost Ck
Lost Ck Res, Croydon, Nr April-July3.3 4.8 6.2 46 6.9 10.5
East Canyon Ck
East Canyon Res, Morgan, Nr April-July8.7 10.6 13.7 51 18 22
Weber
Gateway April-July79 104 142 44 183 275
Sf Ogden
Huntsville, Nr April-July21 29 34 61 45 64
Ogden
Pineview Res, Ogden, Nr April-July29 45 56 50 85 119


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-July18.3 21 24 63 27 32
Big Cottonwood Ck
Salt Lake City, Nr April-July13.1 16.7 21 58 25 31
Mill Ck
Salt Lake City, Nr April-July2 2.5 3 47 3.7 4.9
Dell Fk
Little Dell Res April-July1.1 1.8 2.7 49 3.8 4.3
Lambs Ck
Salt Lake City, Nr April-July1.1 1.6 2.4 45 3 4.4
Parleys Ck
Salt Lake City, Nr April-July3 4.4 6.4 45 8.5 10.5
Emigration Ck
Salt Lake City, Nr April-July0.43 0.88 1.3 32 1.8 2.3
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July0.37 0.45 0.57 30 0.78 1.2
City Ck
Salt Lake City, Nr April-July2.7 3.4 4.1 53 5.2 6.5
S Willow Ck
Grantsville, Nr April-July1.1 1.3 1.6 50 2 2.6


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-July16.2 20 24 35 29 38
Provo
Woodland, Nr April-July49 63 75 75 88 109
Hailstone, Nr April-July53 68 82 75 95 118
Deer Ck Res April-July53 69 85 67 101 130
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July7.2 9.8 12 39 15.1 19
West Canyon Ck
Cedar Fort, Nr April-July0.27 0.38 0.43 24 0.71 1.6
Salt Ck
Nephi Powerplant Div, Blo April-July1.3 2.5 3.2 39 4.2 7.4
Jordan
Utah Lake, Provo, Nr April-July97 125 172 53 198 250

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 57.3 198 103 50.0 173 28.9 55.8
untitled Bear River
Bear Lake, Nr Lifton 1130.7 161 87 578.2 82 703.9 1302.0
untitled Little Bear
Hyrum Reservoir 9.9 95 65 9.8 95 10.3 15.3
untitled Weber
Rockport Res, Wanship, Nr 54.4 158 99 31.6 92 34.5 55.2
Echo Res, Echo, At 51.5 111 70 30.7 66 46.3 73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr 18.4 170 82 15.1 139 10.8 22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr 39.8 118 80 25.3 75 33.8 49.5
untitled Sf Ogden
Causey Res 5.5 171 78 5.0 155 3.2 7.1
untitled Ogden
Pineview Res, Ogden, Nr 71.9 140 65 70.5 137 51.4 110.1
untitled Jordanelle Dam
257.9 106 81 188.9 78 243.6 320.3
untitled Provo
Deer Ck Res 139.4 127 93 131.8 120 110.1 149.7
untitled Dell Fk
Little Dell Res 15.6 -99 76 12.7 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 588.9 78 68 387.3 51 753.0 870.9
untitled
TOTAL 2425.7 120 80 1524.3 75 2029.8 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: B.Bernard, Patrick Kormos