Lower Colorado Water Supply Outlook, April 1, 2020

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-May450 460 470 152 500 530
April-May100 110 120 94 150 180
Tonto Ck
Roosevelt, Nr, Gun Ck, Abv January-May95 96 97 231 102 109
April-May4 5 6 102 11 18
Verde
Tangle Ck, Blo, Horseshoe Dam, Abv January-May225 230 235 150 240 270
April-May14 19 23 64 30 55


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-May92 94 96 171 100 109
April-May18 20 22 133 26 35
Virden, Nr, Blue Ck, Blo January-May113 115 116 153 122 136
April-May22 24 25 119 31 45
Solomon, Nr, Head Of Safford Vly January-May230 235 240 175 255 275
April-May35 42 45 115 60 83
San Carlos Reservoir, Coolidge Dam, At January-May188 190 193 203 210 230
April-May23 25 28 152 47 65
San Francisco
Glenwood, Nr January-May42 43 44 210 49 56
April-May4 5.3 6 82 11 18
Clifton January-May116 118 119 195 126 139
April-May12 13.5 14.6 84 22 35


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-June7.5 7.8 8.1 114 9.3 10.8
April-June1.7 2 2.3 66 3.5 5
Zuni
Black Rock Res, Abv January-May0 0.03 0.05 10.6 0.07 0.1
April-May0 0.03 0.05 50 0.07 0.1
Chevelon Ck
Winslow, Nr, Wildcat Cyn, Blo January-May27 28 29 209 31 32
April-May1 2 3 176 4.5 6

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 1582.2 155 96 1152.2 113 1023.7 1653.0
Horse Mesa 242.2 103 99 239.7 102 235.3 245.1
Mormon Flat 57.0 105 99 56.0 103 54.4 57.9
Stewart Mountain 68.1 106 98 67.2 104 64.4 69.8
Horseshoe 108.5 166 99 106.0 162 65.4 109.2
Bartlett 178.3 129 100 175.1 127 138.0 178.2
untitled
TOTAL 2236.3 141 97 1796.3 114 1581.3 2313.2
Bill Williams
Alamo 194.0 132 19 148.2 101 146.8 1045.0
Agua Fria
Lake Pleasant 813.2 105 93 797.4 103 770.9 869.9
Gila
San Carlos 204.3 49 23 156.3 38 413.8 875.0
Colorado
Lake Powell 11822.0 70 49 9049.0 53 16941.7 24322.0
Lake Mead 11615.0 57 44 10873.4 53 20450.4 26120.0
untitled
TOTAL 24648.5 64 46 21024.4 54 38723.6 53231.9

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