Great Basin Water Supply Outlook, May 1, 2015

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
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	50% Exceedance Volume	Percent Average	10% Exceedance Volume
Bear
Utah	April-July	53	61	54	70
	May-July	43	51	49	60
Woodruff Narrows Rsvr, Abv	April-July	32	36	30	45
	May-July	27	31	30	40
Montpelier, Nr, Stewart Dam, Blo *	April-July	51	58	32	80
	May-July	42	49	34	71
Smiths Fork
Border, Nr	April-July	63	70	79	78
	May-July	50	57	71	65
Logan
Logan, Nr, State Dam, Abv	April-July	48	54	49	62
	May-July	40	46	48	54
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv	April-July	13.4	14.3	33	17.5
	May-July	9.6	10.5	34	13.7
Little Bear
Paradise	April-July	7.8	8.3	17.7	10.2
	May-July	5.4	5.9	18.4	7.8

*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	50% Exceedance Volume	Percent Average	10% Exceedance Volume
Weber
Oakley, Nr	April-July	46	54	46	67
	May-July	36	44	42	57
Rockport Res, Wanship, Nr	April-July	30	38	29	54
	May-July	24	32	28	48
Coalville, Nr	April-July	29	36	27	52
	May-July	21	28	25	44
Chalk Ck
Coalville	April-July	7.5	9.8	24	14.3
	May-July	5.1	7.4	22	11.9
Weber
Echo Res, Echo, At	April-July	35	44	26	64
	May-July	24	33	23	53
Lost Ck
Lost Ck Res, Croydon, Nr	April-July	2.5	2.5	18.7	2.9
	May-July	1.3	1.3	13.4	1.7
East Canyon Ck
East Canyon Res, Morgan, Nr	April-July	6	6.2	23	8
	May-July	4.1	4.3	23	6.1
Weber
Gateway	April-July	48	58	17.8	92
	May-July	29	39	15.9	73
Sf Ogden
Huntsville, Nr	April-July	12.9	13.8	25	18.6
	May-July	7.6	8.5	21	13.3
Ogden
Pineview Res, Ogden, Nr	April-July	16.2	18.1	16	27
	May-July	8.3	10.2	14	19

Six Creeks Specific Site Forecasts (kaf)

Click site name for graph.

	Forecast Period	90% Exceedance Volume	50% Exceedance Volume	Percent Average	10% Exceedance Volume
Little Cottonwood Ck
Salt Lake City, Nr	April-July	16.7	18	47	23
	May-July	14.6	15.9	45	21
Big Cottonwood Ck
Salt Lake City, Nr	April-July	10.1	11.5	32	15.3
	May-July	8.2	9.6	30	13.4
Mill Ck
Salt Lake City, Nr	April-July	1.2	1.3	19.8	1.7
	May-July	0.84	0.91	16.9	1.3
Dell Fk
Little Dell Res	April-July	0.62	0.68	12.4	1.2
	May-July	0.35	0.41	10.5	0.89
Parleys Ck
Salt Lake City, Nr	April-July	1.8	1.9	13.7	2.7
	May-July	1.2	1.4	12.7	2.1
Emigration Ck
Salt Lake City, Nr	April-July	0.46	0.46	11.5	0.73
	May-July	0.4	0.4	14.8	0.67
City Ck
Salt Lake City, Nr	April-July	2.1	2.4	31	3.1
	May-July	1.7	1.9	29	2.6
S Willow Ck
Grantsville, Nr	April-July	0.99	1.1	37	1.6
	May-July	0.76	0.91	34	1.3

Utah Lake Specific Site Forecasts (kaf)

Click site name for graph.

	Forecast Period	90% Exceedance Volume	50% Exceedance Volume	Percent Average	10% Exceedance Volume
Spanish Fork
Castilla, Nr	April-July	12.4	13.4	19.4	16.1
	May-July	8.4	9.4	17.4	12.1
Provo
Woodland, Nr	April-July	48	55	55	64
	May-July	36	43	48	52
Hailstone, Nr	April-July	53	60	55	70
	May-July	40	47	48	57
Deer Ck Res	April-July	46	52	41	63
	May-July	33	39	38	50
American Fork
American Fork, Nr, Up Pwrplnt, Abv	April-July	6.4	7.5	24	11
	May-July	4.9	6	21	9.5
West Canyon Ck
Cedar Fort, Nr	April-July	0.09	0.1	5.7	0.19
	May-July	0.08	0.09	5.8	0.18
Jordan
Utah Lake, Provo, Nr	April-July	81	93	29	118
	May-July	42	54	22	79

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	54.6	121	98	38.1	85	45.0	55.8
untitled Bear River
Bear Lake, Nr Lifton	716.7	93	55	728.7	95	770.8	1302.0
untitled Little Bear
Hyrum Reservoir	14.7	104	96	14.5	102	14.2	15.3
untitled Weber
Rockport Res, Wanship, Nr	44.9	112	81	36.1	90	40.1	55.2
Echo Res, Echo, At	46.3	85	63	43.0	79	54.3	73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr	15.0	113	67	14.7	110	13.3	22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr	31.6	80	64	30.7	78	39.5	49.5
untitled Sf Ogden
Causey Res	7.1	142	101	5.9	117	5.0	7.1
untitled Ogden
Pineview Res, Ogden, Nr	77.2	97	70	83.0	104	79.7	110.1
untitled Jordanelle Dam
	215.0	86	67	173.1	69	251.3	320.3
untitled Provo
Deer Ck Res	145.3	118	97	133.6	108	123.5	149.7
untitled Dell Fk
Little Dell Res	12.8	-99	62	13.3	-99	-9999.0	20.5
untitled Jordan
Utah Lake, Provo, Nr	-9999.0	-99	-99	684.3	83	827.8	870.9
untitled
TOTAL	1368.4	95	63	1985.7	88	1436.7	2181.9

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