Great Basin Water Supply Outlook, June 1, 2023

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

Prepared by Patrick Kormos
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	130	143	146	134	153	160
	June-July	58	71	74	117	81	88
Woodruff Narrows Rsvr, Abv	April-July	154	173	188	174	194	205
	June-July	29	48	63	124	69	81
Stewart Dam *	April-July	240	270	310	193	345	365
	June-July	64	94	133	164	169	187
Smiths Fork
Border, Nr	April-July	97	101	105	119	109	115
	June-July	46	50	54	110	58	64
Logan
Logan, Nr, State Dam, Abv	April-July	160	169	176	166	181	189
	June-July	82	91	98	172	103	111
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv	April-July	78	82	87	235	91	95
	June-July	23	27	32	227	36	40
Little Bear
Paradise	April-July	82	84	86	221	93	101
	June-July	8.4	10.4	12.4	132	19.4	27

*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	134	140	150	135	156	165
	June-July	52	58	68	115	74	83
Rockport Res, Wanship, Nr	April-July	164	173	185	161	200	215
	June-July	54	63	75	136	90	105
Coalville, Nr	April-July	190	200	210	176	235	255
	June-July	61	71	79	144	104	126
Chalk Ck
Coalville	April-July	56	79	62	177	66	75
	June-July	11.8	35	17.5	131	22	31
Weber
Echo Reservoir, Echo, At	April-July	240	260	270	178	290	315
	June-July	67	87	96	145	117	142
Lost Ck
Lost Ck Reservoir, Croyden, Nr	April-July	29	30	31	242	33	35
	June-July	2.8	3.8	5.1	165	6.8	8.8
East Canyon Ck
East Canyon Reservoir, Morgan, Nr	April-July	57	59	62	270	65	67
	June-July	10.2	12.2	15.6	226	18.2	20
Weber
Gateway	April-July	560	580	605	220	655	700
	June-July	114	134	160	174	210	255
Sf Ogden
Huntsville, Nr	April-July	102	106	110	212	115	122
	June-July	14.8	18.8	23	178	28	35
Ogden
Pineview Reservoir, Ogden, Nr	April-July	235	245	255	234	270	280
	June-July	28	38	48	209	63	73

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	54	56	59	174	62	65
	June-July	35	37	40	182	43	46
Big Cottonwood Ck
Salt Lake City, Nr	April-July	57	60	63	185	70	76
	June-July	36	39	42	239	49	55
Mill Ck
Salt Lake City, Nr	April-July	9.4	10	10.5	202	11.1	11.8
	June-July	4.9	5.5	6	222	6.6	7.3
Dell Fk
Little Dell Reservoir	April-July	9.3	9.7	10.1	230	10.6	11.6
	June-July	0.99	1.4	1.8	135	2.3	3.3
Lambs Ck
Salt Lake City, Nr	April-July	8.6	9.5	10.5	244	11.7	13.2
	June-July	1.8	2.7	3.7	161	4.9	6.4
Parleys Ck
Salt Lake City, Nr	April-July	23	26	28	243	30	33
	June-July	2.7	5.2	6.9	147	8.9	12.2
Red Butte Ck
Ft Douglas, At, Salt Lake City, Nr	April-July	2.8	3.2	3.4	218	3.5	3.7
	June-July	0.24	0.64	0.86	179	0.94	1.1
City Ck
Salt Lake City, Nr	April-July	10.1	10.9	11.5	177	12	12.8
	June-July	4.5	5.3	5.9	190	6.4	7.2

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	130	140	154	285	158	162
	June-July	17.2	27	41	222	45	49
Provo
Woodland, Nr	April-July	134	143	159	166	165	170
	June-July	52	61	77	171	83	88
Hailstone, Nr	April-July	155	170	186	175	195	205
	June-July	51	66	82	171	91	101
Deer Ck Reservoir	April-July	225	235	265	223	275	295
	June-July	66	78	107	214	118	138
American Fork
American Fork, Nr, Up Pwrplnt, Abv	April-July	56	60	63	252	65	69
	June-July	33	37	40	252	42	46
West Canyon Ck
Cedar Fort, Nr	April-July	2.9	3.2	3.4	195	3.6	4
	June-July	1.3	1.6	1.8	203	2	2.4
Salt Ck
Nephi Powerplant Div, Blo	April-July	24	26	27	346	29	32
	June-July	6.6	8.6	9.7	313	11.6	14.6
Jordan
Utah Lake, Provo, Nr	April-July	660	690	755	351	785	850
	June-July	181	210	275	217	305	370

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	63.4	135	114	39.0	83	47.1	55.8
untitled Bear River
Bear Lake, Nr Lifton	822.4	99	63	726.0	87	829.8	1302.0
untitled Little Bear
Hyrum Reservoir	10.6	73	70	14.5	99	14.6	15.3
untitled Weber
Rockport Res, Wanship, Nr	41.9	83	76	58.7	116	50.5	55.2
Echo Reservoir, Echo, At	54.6	85	74	60.4	94	64.4	73.9
untitled Lost Ck
Lost Ck Reservoir, Croyden, Nr	22.7	124	101	15.1	82	18.4	22.5
untitled East Canyon Ck
East Canyon Reservoir, Morgan, Nr	45.7	100	92	38.5	84	45.6	49.5
untitled Sf Ogden
Causey Reservoir	7.2	102	101	7.1	100	7.0	7.1
untitled Ogden
Pineview Res, Ogden, Nr	94.9	95	86	72.2	72	99.7	110.1
untitled Provo
Jordanelle Reservoir	293.5	113	92	220.0	85	258.7	320.3
Deer Ck Reservoir	143.8	110	96	126.3	97	130.6	149.7
untitled Dell Fk
Little Dell Reservoir	16.8	-99	82	11.9	-99	-9999.0	20.5
untitled Jordan
Utah Lake, Provo, Nr	764.4	91	88	507.6	60	844.2	870.9
untitled
TOTAL	2365.0	98	78	1885.4	78	2410.4	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 1991-2020 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: Patrick Kormos