Lower Colorado Water Supply Outlook, April 1, 2021

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.

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

	Forecast Period	90% Exceedance Volume	70% Exceedance Volume	50% Exceedance Volume	Percent Median	30% Exceedance Volume	10% Exceedance Volume
Salt
Roosevelt, Nr	January-May	41	42	43	13.9	44	46
	April-May	14.5	15.5	16.2	12.8	17.5	20
Tonto Ck
Roosevelt, Nr, Gun Ck, Abv	January-May	3.5	3.7	3.9	9.3	4.2	4.5
	April-May	0	0.2	0.4	6.8	0.7	1
Verde
Tangle Ck, Blo, Horseshoe Dam, Abv	January-May	53	54	55	35	56	59
	April-May	11	11.5	12.5	35	14	17

	Forecast Period	90% Exceedance Volume	70% Exceedance Volume	50% Exceedance Volume	Percent Median	30% Exceedance Volume	10% Exceedance Volume
Gila
Gila, Nr	January-May	14.6	14.8	15	27	15.3	15.9
	April-May	4.7	4.9	5.1	31	5.4	6
Virden, Nr, Blue Ck, Blo	January-May	18.5	18.7	19	25	19.5	20
	April-May	4.9	5.1	5.4	26	5.9	6.7
Solomon, Nr, Head Of Safford Vly	January-May	25	26	27	19.7	28	29
	April-May	7.2	8	8.5	22	9.5	11
San Carlos Reservoir, Coolidge Dam, At	January-May	6.4	7.4	7.9	8.3	8.4	9.9
	April-May	0	1	1.5	8.2	2	3.5
San Francisco
Glenwood, Nr	January-May	4.7	4.9	5.1	24	5.3	5.5
	April-May	1.5	1.7	1.9	26	2.1	2.3
Clifton	January-May	11.8	12	12.3	20	12.7	13.5
	April-May	3.5	3.7	4	23	4.4	5.2

	Forecast Period	90% Exceedance Volume	70% Exceedance Volume	50% Exceedance Volume	Percent Median	30% Exceedance Volume	10% Exceedance Volume
Little Colorado
Lyman Lk, Abv, St. Johns, Nr	January-June	0.41	0.51	0.61	8.6	0.71	0.91
	April-June	0.1	0.2	0.3	8.6	0.4	0.6
Zuni
Black Rock Res, Abv	January-May	0	0	0	0	0	0.1
	April-May	0	0	0	0	0	0.1
Chevelon Ck
Winslow, Nr, Wildcat Cyn, Blo	January-May	0	0	0.1	0.72	0.2	0.3
	April-May	0	0	0.1	5.9	0.2	0.3

	EOM Contents	Percent EOM Average	Percent Usable Capacity	Last Year EOM	Last Year %Average	EOM Average	Usable Capacity
Salt
Roosevelt	1302.5	127	79	1582.2	155	1023.7	1653.0
Horse Mesa	230.5	98	94	242.2	103	235.3	245.1
Mormon Flat	55.3	102	96	57.0	105	54.4	57.9
Stewart Mountain	65.4	101	94	68.1	106	64.4	69.8
Horseshoe	6.5	10	6	108.5	166	65.4	109.2
Bartlett	85.5	62	48	178.3	129	138.0	178.2
untitled
TOTAL	1745.7	110	75	2236.3	141	1581.3	2313.2


Bill Williams
Alamo	117.1	80	11	194.0	132	146.8	1045.0
Agua Fria
Lake Pleasant	798.7	104	92	813.2	105	770.9	869.9
Gila
San Carlos	8.8	2	1	204.3	49	413.8	875.0
Colorado
Lake Powell	8843.8	52	36	11822.0	70	16941.7	24322.0
Lake Mead	10388.2	51	40	11615.0	57	20450.4	26120.0
untitled
TOTAL	20039.5	52	38	24648.5	64	38576.8	52186.9

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

Lower Colorado Water Supply Outlook, April 1, 2021

Lower Colorado Summary

Salt Basin Conditions

Gila Basin Conditions

Little Colorado Basin Conditions

Salt Specific Site Forecasts (kaf)

Gila Specific Site Forecasts (kaf)

Little Colorado Specific Site Forecasts (kaf)

Lower Colorado End of Month Reservoir Contents (kaf)

Precipitation Maps

Definitions

Additional Information