Great Basin Water Supply Outlook, May 1, 2017

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.

Prepared by 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	167	173	180	161	189	198
	May-July	154	160	167	161	176	185
Woodruff Narrows Rsvr, Abv	April-July	175	192	205	169	215	235
	May-July	140	157	172	164	181	200
Montpelier, Nr, Stewart Dam, Blo *	April-July	550	580	600	330	625	665
	May-July	370	400	420	290	445	485
Smiths Fork
Border, Nr	April-July	155	162	171	192	181	187
	May-July	128	135	144	180	154	160
Logan
Logan, Nr, State Dam, Abv	April-July	210	220	230	207	240	250
	May-July	174	188	197	205	205	215
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv	April-July	89	95	100	233	104	111
	May-July	58	64	69	223	73	80
Little Bear
Paradise	April-July	82	88	94	200	102	111
	May-July	50	56	62	194	70	79

*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	160	170	180	153	190	200
	May-July	140	150	160	151	170	182
Rockport Res, Wanship, Nr	April-July	177	189	200	152	210	240
	May-July	149	161	172	152	182	210
Coalville, Nr	April-July	180	191	205	153	215	245
	May-July	150	161	175	155	185	215
Chalk Ck
Coalville	April-July	55	61	65	159	71	78
	May-July	41	47	51	150	57	64
Weber
Echo Res, Echo, At	April-July	240	255	270	158	285	320
	May-July	192	210	225	157	240	275
Lost Ck
Lost Ck Res, Croydon, Nr	April-July	30	32	33	246	35	39
	May-July	18.4	19.8	21	219	23	27
East Canyon Ck
East Canyon Res, Morgan, Nr	April-July	30	33	35	130	39	43
	May-July	20	23	25	132	29	33
Weber
Gateway	April-July	460	490	530	163	580	660
	May-July	330	360	400	163	450	530
Sf Ogden
Huntsville, Nr	April-July	90	98	102	182	111	121
	May-July	57	65	69	173	78	88
Ogden
Pineview Res, Ogden, Nr	April-July	180	194	205	181	225	250
	May-July	108	122	134	184	155	178

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	47	50	53	139	55	59
	May-July	43	46	49	140	51	55
Big Cottonwood Ck
Salt Lake City, Nr	April-July	42	45	48	133	50	54
	May-July	36	39	42	131	44	48
Mill Ck
Salt Lake City, Nr	April-July	6.1	6.8	7.2	113	7.6	8.3
	May-July	5.3	6	6.4	119	6.8	7.5
Dell Fk
Little Dell Res	April-July	4.5	4.9	5.4	98	5.9	6.6
	May-July	3.2	3.6	4.1	105	4.6	5.3
Parleys Ck
Salt Lake City, Nr	April-July	14	15.3	16.4	115	17.5	19.8
	May-July	10	11.3	12.4	117	13.5	15.8
Emigration Ck
Salt Lake City, Nr	April-July	3.7	4.1	4.4	110	4.9	5.6
	May-July	2.3	2.7	3	111	3.5	4.2
City Ck
Salt Lake City, Nr	April-July	8.3	8.8	9.3	121	10.2	10.9
	May-July	6.7	7.2	7.7	118	8.6	9.3
S Willow Ck
Grantsville, Nr	April-July	3.3	3.6	3.9	126	4.2	4.7
	May-July	2.6	2.9	3.2	119	3.5	4

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	68	69	78	113	84	90
	May-July	45	46	55	102	61	67
Provo
Woodland, Nr	April-July	155	161	167	167	178	188
	May-July	136	142	148	166	159	169
Hailstone, Nr	April-July	171	178	184	167	194	205
	May-July	152	159	165	170	175	185
Deer Ck Res	April-July	220	230	245	193	260	275
	May-July	180	190	205	197	220	235
American Fork
American Fork, Nr, Up Pwrplnt, Abv	April-July	39	42	45	145	47	51
	May-July	35	38	41	146	43	47
West Canyon Ck
Cedar Fort, Nr	April-July	2.2	2.5	2.9	165	3.3	3.9
	May-July	1.8	2.1	2.5	162	2.9	3.5
Jordan
Utah Lake, Provo, Nr	April-July	490	525	555	171	580	610
	May-July	375	410	440	176	465	495

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	50.4	112	90	56.4	125	45.0	55.8
untitled Bear River
Bear Lake, Nr Lifton	1002.3	130	77	674.3	87	770.8	1302.0
untitled Little Bear
Hyrum Reservoir	10.4	73	68	13.1	92	14.2	15.3
untitled Weber
Rockport Res, Wanship, Nr	26.9	67	49	45.1	113	40.1	55.2
Echo Res, Echo, At	49.4	91	67	49.1	91	54.3	73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr	18.5	139	82	16.3	122	13.3	22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr	43.5	110	88	32.6	82	39.5	49.5
untitled Sf Ogden
Causey Res	7.2	143	101	7.1	142	5.0	7.1
untitled Ogden
Pineview Res, Ogden, Nr	74.6	94	68	103.3	130	79.7	110.1
untitled Jordanelle Dam
	254.9	101	80	182.8	73	251.3	320.3
untitled Provo
Deer Ck Res	146.6	119	98	144.4	117	123.5	149.7
untitled Dell Fk
Little Dell Res	13.6	-99	66	12.0	-99	-9999.0	20.5
untitled Jordan
Utah Lake, Provo, Nr	575.1	69	66	486.1	59	827.8	870.9
untitled
TOTAL	2259.7	100	74	1810.6	80	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: B.Bernard