Lower Colorado Water Supply Outlook, January 1, 2021

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by Z. Finch
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Lower Colorado Summary






*Median of forecasts within each basin.


Salt Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Gila Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Little Colorado Basin Conditions




Snow Water Equivalent in Percent of Median.
* Percent usable capacity, not percent average contents.
Click for multi-month Graph.


Salt Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Median		30%
Exceedance
Volume		10%
Exceedance
Volume
Salt
Roosevelt, Nr January-May34 51 77 25 101 195
Tonto Ck
Roosevelt, Nr, Gun Ck, Abv January-May0.3 2.5 6.4 15.2 18.1 45
Verde
Tangle Ck, Blo, Horseshoe Dam, Abv January-May41 49 65 41 105 167


Gila Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		70%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Median		30%
Exceedance
Volume		10%
Exceedance
Volume
Gila
Gila, Nr January-May14 15.1 17.6 31 25 42
Virden, Nr, Blue Ck, Blo January-May15.5 18.5 22 29 33 62
Solomon, Nr, Head Of Safford Vly January-May26 34 41 30 63 114
San Carlos Reservoir, Coolidge Dam, At January-May12 19 25 26 45 80
San Francisco
Glenwood, Nr January-May5 5.2 6.6 31 10 19.4
Clifton January-May10.7 12 15.9 26 23 42


Little Colorado Specific Site Forecasts (kaf)

Click site name for graph.
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-June0.7 1 1.3 18.3 1.9 3.1
Zuni
Black Rock Res, Abv January-May0 0 0 0 0.1 0.3
Chevelon Ck
Winslow, Nr, Wildcat Cyn, Blo January-May0 1.1 1.8 12.9 3.9 7.7

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).

Lower Colorado End of Month Reservoir Contents (kaf)

EOM
Contents		Percent
EOM
Average		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Average		EOM
Average		Usable
Capacity
Salt
Roosevelt 1324.3 158 80 1157.9 138 838.9 1653.0
Horse Mesa 222.0 102 91 233.0 107 218.0 245.1
Mormon Flat 55.4 104 96 56.3 106 53.3 57.9
Stewart Mountain 65.1 105 93 67.1 109 61.8 69.8
Horseshoe 7.9 25 7 44.4 142 31.3 109.2
Bartlett 85.4 80 48 123.9 116 107.0 178.2
untitled
TOTAL 1760.1 134 76 1682.6 128 1310.2 2313.2
Bill Williams
Alamo 121.1 94 12 161.2 126 128.4 1045.0
Agua Fria
Lake Pleasant 666.4 126 77 735.4 140 527.0 869.9
Gila
San Carlos 22.9 7 3 47.5 15 324.9 875.0
Colorado
Lake Powell 10149.1 57 42 12603.9 71 17744.8 24322.0
Lake Mead 10319.9 51 40 10886.4 54 20297.1 26120.0
untitled
TOTAL 21158.3 54 41 24273.2 62 38893.9 52186.9

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:
RangeRound to
0-1.990.01
2.0-19.90.1
20-1991.0
200-9995.0
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: Z. Finch