Great Basin Water Supply Outlook, April 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-July75 85 90 80 104 119
Woodruff Narrows Rsvr, Abv April-July62 70 79 65 90 119
Montpelier, Nr, Stewart Dam, Blo * April-July41 52 67 37 85 134
Smiths Fork
Border, Nr April-July65 69 77 87 84 96
Logan
Logan, Nr, State Dam, Abv April-July83 87 96 86 107 125
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July28 30 31 72 35 44
Little Bear
Paradise April-July16.1 18.7 22 47 29 35

*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-July53 57 63 53 78 96
Rockport Res, Wanship, Nr April-July45 51 57 43 74 97
Coalville, Nr April-July44 51 56 42 74 98
Chalk Ck
Coalville April-July11.6 13.4 16.1 39 23 32
Weber
Echo Res, Echo, At April-July49 62 73 43 99 137
Lost Ck
Lost Ck Res, Croydon, Nr April-July3.9 4.8 5.3 40 6.1 9.4
East Canyon Ck
East Canyon Res, Morgan, Nr April-July10.7 12.2 13.7 51 16.6 22
Weber
Gateway April-July83 106 122 38 177 230
Sf Ogden
Huntsville, Nr April-July27 30 32 57 40 54
Ogden
Pineview Res, Ogden, Nr April-July38 45 50 44 67 93


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-July20 22 24 63 27 30
Big Cottonwood Ck
Salt Lake City, Nr April-July17.8 20 22 61 25 29
Mill Ck
Salt Lake City, Nr April-July2.4 2.7 2.9 45 3.3 4.4
Dell Fk
Little Dell Res April-July1.5 1.9 2.4 44 3 4.2
Lambs Ck
Salt Lake City, Nr April-July1.3 1.6 2 38 2.6 4.1
Parleys Ck
Salt Lake City, Nr April-July3.7 4.9 5.6 39 6.9 9.9
Emigration Ck
Salt Lake City, Nr April-July0.6 0.79 1 26 1.4 1.7
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July0.4 0.43 0.47 25 0.5 0.68
City Ck
Salt Lake City, Nr April-July3 3.4 3.9 51 4.4 5.7
S Willow Ck
Grantsville, Nr April-July1.1 1.2 1.4 45 1.7 2.1


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-July17.1 18.9 21 30 24 28
Provo
Woodland, Nr April-July47 55 61 61 67 81
Hailstone, Nr April-July53 61 64 58 72 87
Deer Ck Res April-July54 64 70 55 78 94
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July9.2 10.3 11.7 38 13.6 15.4
West Canyon Ck
Cedar Fort, Nr April-July0.3 0.33 0.36 20 0.6 0.96
Salt Ck
Nephi Powerplant Div, Blo April-July2.2 2.6 3.1 37 3.6 4.7
Jordan
Utah Lake, Provo, Nr April-July104 123 129 40 163 180

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 57.8 151 103 48.7 127 38.2 55.8
untitled Bear River
Bear Lake, Nr Lifton 1121.7 153 86 809.8 111 731.1 1302.0
untitled Little Bear
Hyrum Reservoir 11.8 90 77 10.5 81 13.0 15.3
untitled Weber
Rockport Res, Wanship, Nr 54.8 146 99 26.7 71 37.6 55.2
Echo Res, Echo, At 65.8 131 89 35.3 70 50.2 73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr 19.6 176 87 15.6 140 11.2 22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr 44.4 125 90 37.1 104 35.5 49.5
untitled Sf Ogden
Causey Res 6.8 211 96 7.2 223 3.2 7.1
untitled Ogden
Pineview Res, Ogden, Nr 86.4 138 78 56.1 90 62.7 110.1
untitled Jordanelle Dam
256.5 106 80 215.2 89 242.0 320.3
untitled Provo
Deer Ck Res 149.6 125 100 148.1 124 119.4 149.7
untitled Dell Fk
Little Dell Res 15.4 -99 75 12.8 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 637.5 78 73 514.3 63 812.8 870.9
untitled
TOTAL 2512.6 116 83 1924.6 89 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: B.Bernard, Patrick Kormos