San Juan Water Supply Outlook, May 1, 2021

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

Contents

San Juan Summary






*Median of forecasts within each basin.


San Juan Basin Conditions




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


San Juan 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
San Juan
Pagosa Springs April-July103 114 122 57 133 150
May-July75 86 94 52 105 122
Carracas, Nr April-July173 190 205 54 220 255
May-July128 145 160 53 175 210
Navajo Reservoir, Archuleta, Nr April-July265 295 325 44 345 410
May-July186 215 245 43 265 330
Farmington April-July330 365 405 37 460 610
May-July250 285 325 37 380 530
Bluff, Nr April-July300 335 375 34 440 590
May-July220 255 295 35 360 510
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July29 32 34 63 38 43
May-July21 24 26 58 30 35
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July34 37 39 60 43 49
May-July26 29 31 57 35 41
Little Navajo
Oso Div Dam,bl,chromo,nr April-July3.1 3.5 3.9 51 4.3 5.1
May-July2 2.4 2.8 52 3.2 4
Piedra
Arboles, Nr April-July68 81 90 43 100 119
May-July46 59 68 44 78 97
Los Pinos
Vallecito Reservoir, Bayfield, Nr April-July71 80 92 47 102 119
May-July57 66 78 46 88 105
Animas
Durango April-July118 145 164 40 193 250
May-July100 127 146 40 175 230
Florida
Lemon Reservoir, Durango, Nr April-July14.5 17 19.5 35 23 28
May-July12 14.5 17 35 20 25
La Plata
Hesperus April-July5 6.1 7 30 8.2 10.5
May-July3.5 4.6 5.5 30 6.7 9
Mancos
Mancos, Nr April-July5.5 6.3 7.5 24 8.5 10.5
May-July4 4.8 6 25 7 9

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).

San Juan 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 Los Pinos
Vallecito Reservoir, Bayfield, Nr 56.6 76 45 95.1 128 74.0 125.4
untitled San Juan
Navajo Reservoir, Archuleta, Nr 1044.6 77 62 1296.8 95 1361.0 1696.0
untitled Florida
Lemon Reservoir, Durango, Nr 13.2 55 33 19.8 82 24.1 39.8
untitled
TOTAL 1114.4 76 60 1411.7 97 1459.0 1861.2

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: Ashley Nielson