Great Basin Water Supply Outlook, May 1, 2016

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, B.Bernard
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Water Supply Forecast Discussion
Bear Basin Conditions
Weber Basin Conditions
Six Creeks Basin Conditions
Utah Lake Basin Conditions
Bear Specific Site Forecasts
Weber Specific Site Forecasts
Six Creeks Specific Site Forecasts
Utah Lake Specific Site Forecasts
Reservoir Contents
Precipitation Maps
Definitions
Additional Information
Questions or Comments

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-July	80	88	93	83	97	108
	May-July	73	81	86	83	90	101
Woodruff Narrows Rsvr, Abv	April-July	63	69	76	63	81	91
	May-July	53	59	66	63	71	81
Montpelier, Nr, Stewart Dam, Blo *	April-July	69	78	82	45	92	107
	May-July	50	59	63	43	73	88
Smiths Fork
Border, Nr	April-July	62	66	69	78	73	77
	May-July	51	55	58	73	62	66
Logan
Logan, Nr, State Dam, Abv	April-July	88	92	94	85	99	105
	May-July	71	75	77	80	82	88
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv	April-July	35	35	36	84	38	42
	May-July	24	24	25	81	27	31
Little Bear
Paradise	April-July	23	23	25	53	27	31
	May-July	10.9	11.7	13.3	42	15.2	19

*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-July	77	86	92	78	95	107
	May-July	67	76	82	77	85	97
Rockport Res, Wanship, Nr	April-July	69	80	86	65	89	103
	May-July	58	69	75	66	78	92
Coalville, Nr	April-July	67	78	84	63	88	102
	May-July	54	65	71	63	75	89
Chalk Ck
Coalville	April-July	17	18.7	22	54	23	28
	May-July	12.9	14.6	17.7	52	19.3	24
Weber
Echo Res, Echo, At	April-July	80	94	102	60	108	127
	May-July	63	77	85	59	91	110
Lost Ck
Lost Ck Res, Croydon, Nr	April-July	8	8.1	8.5	63	9.2	10.3
	May-July	3.6	3.7	4.1	43	4.8	5.9
East Canyon Ck
East Canyon Res, Morgan, Nr	April-July	12.5	12.8	13.3	49	14.4	16.9
	May-July	8	8.3	8.8	47	9.9	12.4
Weber
Gateway	April-July	152	170	180	55	191	235
	May-July	97	115	125	51	136	178
Sf Ogden
Huntsville, Nr	April-July	45	47	49	88	54	63
	May-July	24	26	28	70	33	42
Ogden
Pineview Res, Ogden, Nr	April-July	72	76	80	71	88	101
	May-July	37	41	45	62	53	66

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-July	26	27	28	74	29	33
	May-July	24	25	26	74	27	31
Big Cottonwood Ck
Salt Lake City, Nr	April-July	19.9	21	21	58	22	26
	May-July	17.1	17.8	18.5	58	19.5	23
Mill Ck
Salt Lake City, Nr	April-July	2.6	2.9	3	47	3.2	3.9
	May-July	2.2	2.5	2.6	48	2.8	3.5
Dell Fk
Little Dell Res	April-July	2.3	2.6	2.7	49	3	3.6
	May-July	2	2.2	2.3	59	2.6	3.2
Parleys Ck
Salt Lake City, Nr	April-July	5.7	6.1	6.4	45	7.1	9
	May-July	4.5	4.9	5.2	49	5.9	7.8
Emigration Ck
Salt Lake City, Nr	April-July	0.9	0.94	0.99	25	1.2	1.4
	May-July	0.72	0.76	0.81	30	0.97	1.3
City Ck
Salt Lake City, Nr	April-July	4.2	4.4	4.6	60	4.9	5.6
	May-July	3.6	3.8	4	62	4.3	5
S Willow Ck
Grantsville, Nr	April-July	2.1	2.2	2.3	74	2.4	2.7
	May-July	1.6	1.7	1.8	66	1.9	2.2

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-July	16.8	17.5	18.8	27	19.3	22
	May-July	13.4	14.1	15.4	29	15.9	18.3
Provo
Woodland, Nr	April-July	66	73	75	75	80	87
	May-July	56	63	65	73	70	77
Hailstone, Nr	April-July	74	81	83	75	89	96
	May-July	62	69	71	73	77	84
Deer Ck Res	April-July	78	86	90	71	100	107
	May-July	62	70	74	71	84	91
American Fork
American Fork, Nr, Up Pwrplnt, Abv	April-July	15.1	16.3	17.2	55	17.9	22
	May-July	13.2	14.4	15.3	55	16	20
West Canyon Ck
Cedar Fort, Nr	April-July	0.62	0.78	1	58	1.2	1.6
	May-July	0.61	0.77	1	66	1.2	1.6
Jordan
Utah Lake, Provo, Nr	April-July	144	156	167	51	182	200
	May-July	102	114	125	50	140	160

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	56.4	125	101	54.6	121	45.0	55.8
untitled Bear River
Bear Lake, Nr Lifton	674.3	87	52	716.7	93	770.8	1302.0
untitled Little Bear
Hyrum Reservoir	13.1	92	86	14.7	104	14.2	15.3
untitled Weber
Rockport Res, Wanship, Nr	45.1	113	82	44.9	112	40.1	55.2
Echo Res, Echo, At	49.1	91	66	46.3	85	54.3	73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr	16.3	122	72	15.0	113	13.3	22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr	32.6	82	66	31.6	80	39.5	49.5
untitled Sf Ogden
Causey Res	7.1	142	101	7.1	142	5.0	7.1
untitled Ogden
Pineview Res, Ogden, Nr	103.3	130	94	77.2	97	79.7	110.1
untitled Jordanelle Dam
	180.1	72	56	212.4	85	251.3	320.3
untitled Provo
Deer Ck Res	144.4	117	96	145.3	118	123.5	149.7
untitled Dell Fk
Little Dell Res	12.0	-99	58	12.9	-99	-9999.0	20.5
untitled Jordan
Utah Lake, Provo, Nr	486.1	59	56	554.7	67	827.8	870.9
untitled
TOTAL	1807.9	80	60	1920.4	85	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:

Range		Round to
0-1.99		0.01
2.0-19.9		0.1
20-199		1.0
200-999		5.0
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, B.Bernard