Great Basin Water Supply Outlook, May 1, 2019

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-July118 123 130 116 137 149
May-July110 115 121 116 129 141
Woodruff Narrows Rsvr, Abv April-July127 132 142 117 150 170
May-July95 100 111 106 118 138
Montpelier, Nr, Stewart Dam, Blo * April-July136 150 161 88 185 220
May-July98 112 123 85 147 182
Smiths Fork
Border, Nr April-July65 72 76 85 80 88
May-July56 63 67 84 71 79
Logan
Logan, Nr, State Dam, Abv April-July115 121 125 113 128 140
May-July99 105 109 114 112 124
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July56 62 64 149 67 74
May-July40 46 48 155 51 58
Little Bear
Paradise April-July54 57 59 126 63 74
May-July31 34 36 113 40 51

*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-July115 121 134 114 138 146
May-July102 108 121 114 125 133
Rockport Res, Wanship, Nr April-July135 141 151 114 156 174
May-July110 116 126 112 131 149
Coalville, Nr April-July142 149 158 118 164 183
May-July112 119 128 113 134 153
Chalk Ck
Coalville April-July46 47 51 124 58 65
May-July36 37 41 121 48 55
Weber
Echo Reservoir, Echo, At April-July188 194 210 123 220 250
May-July148 154 170 119 182 210
Lost Ck
Lost Ck Reservoir, Croyden, Nr April-July18.1 19.6 20 149 22 27
May-July11 12.5 13 135 14.6 19.5
East Canyon Ck
East Canyon Reservoir, Morgan, Nr April-July36 38 40 148 42 47
May-July21 23 25 132 27 32
Weber
Gateway April-July410 430 445 137 470 545
May-July275 295 310 127 335 410
Sf Ogden
Huntsville, Nr April-July81 85 88 157 95 110
May-July52 56 59 148 66 81
Ogden
Pineview Reservoir, Ogden, Nr April-July170 178 184 163 195 225
May-July95 103 109 149 120 148


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-July44 47 49 129 51 55
May-July41 44 46 131 48 52
Big Cottonwood Ck
Salt Lake City, Nr April-July38 41 43 119 47 51
May-July33 36 38 119 42 46
Mill Ck
Salt Lake City, Nr April-July5.4 6.1 6.8 106 7.1 7.8
May-July4.3 5 5.7 106 6 6.7
Dell Fk
Little Dell Reservoir April-July6.1 6.5 6.9 125 7.3 8.3
May-July4 4.4 4.8 123 5.2 6.2
Lambs Ck
Salt Lake City, Nr April-July6.2 6.8 7.1 134 7.5 8.5
May-July4.4 5 5.3 126 5.7 6.7
Parleys Ck
Salt Lake City, Nr April-July13.8 17 18.2 128 19.3 22
May-July8 11.2 12.4 117 13.5 15.9
Emigration Ck
Salt Lake City, Nr April-July3.6 4 4.3 108 4.8 5.4
May-July1.5 1.9 2.2 81 2.7 3.3
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr April-July2 2.2 2.4 126 2.6 2.8
May-July1.1 1.3 1.5 0 1.7 1.9
City Ck
Salt Lake City, Nr April-July7.3 8 8.5 110 9.1 9.9
May-July6 6.7 7.2 111 7.8 8.6
S Willow Ck
Grantsville, Nr April-July2.7 3.2 3.6 116 3.9 4.4
May-July1.6 2.1 2.5 93 2.8 3.3


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-July101 114 119 172 124 137
May-July72 85 90 167 95 108
Provo
Woodland, Nr April-July104 118 123 123 131 140
May-July89 103 108 121 116 125
Hailstone, Nr April-July121 134 138 125 148 157
May-July100 113 117 121 127 136
Deer Ck Reservoir April-July152 169 177 139 190 199
May-July120 137 145 139 158 167
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July37 41 43 139 45 49
May-July34 38 40 143 42 46
West Canyon Ck
Cedar Fort, Nr April-July2 2.5 2.8 159 3.1 4.1
May-July1.6 2.1 2.4 156 2.7 3.7
Salt Ck
Nephi Powerplant Div, Blo April-July19.4 23 25 301 26 30
May-July15 19 21 318 22 26
Jordan
Utah Lake, Provo, Nr April-July425 475 505 155 535 585
May-July320 350 380 152 410 460

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 57.9 129 104 59.0 131 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 1036.2 134 80 1147.5 149 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 13.0 92 85 13.8 97 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 41.5 103 75 55.8 139 40.1 55.2
Echo Reservoir, Echo, At 50.1 92 68 72.3 133 54.3 73.9
untitled Lost Ck
Lost Ck Reservoir, Croyden, Nr 21.5 161 95 21.4 161 13.3 22.5
untitled East Canyon Ck
East Canyon Reservoir, Morgan, Nr 42.1 107 85 47.6 121 39.5 49.5
untitled Sf Ogden
Causey Reservoir 6.6 132 94 7.1 141 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 80.0 100 73 105.3 132 79.7 110.1
untitled Provo
Jordanelle Reservoir 219.4 87 69 265.6 106 251.3 320.3
Deer Ck Reservoir 145.6 118 97 148.1 120 123.5 149.7
untitled Dell Fk
Little Dell Reservoir 14.6 -99 71 16.1 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 639.3 77 73 648.9 78 827.8 870.9
untitled
TOTAL 2353.1 104 78 2592.5 114 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