San Juan Water Supply Outlook, June 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-July115 122 128 60 133 140
June-July27 34 40 42 45 52
Carracas, Nr April-July183 193 205 54 215 230
June-July47 57 69 44 80 95
Navajo Reservoir, Archuleta, Nr April-July300 315 335 46 355 380
June-July50 64 83 29 104 130
Farmington April-July390 420 450 41 495 535
June-July90 120 153 33 195 235
Bluff, Nr April-July360 395 420 38 460 505
June-July75 107 134 30 175 220
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July30 32 34 63 36 38
June-July8 9.5 11.7 51 13.8 15.5
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July34 36 39 60 41 44
June-July10 11.2 14.6 49 16.8 20
Little Navajo
Oso Div Dam,bl,chromo,nr April-July3.1 3.2 3.3 43 3.4 3.5
June-July0.3 0.4 0.5 25 0.61 0.7
Piedra
Arboles, Nr April-July84 88 94 45 100 107
June-July17 21 27 36 33 40
Los Pinos
Vallecito Reservoir, Bayfield, Nr April-July95 104 110 57 117 127
June-July31 40 46 46 53 63
Animas
Durango April-July147 160 176 42 190 210
June-July57 70 86 39 100 121
Florida
Lemon Reservoir, Durango, Nr April-July22 23 25 45 27 29
June-July5.5 7.2 8.8 33 11 13
La Plata
Hesperus April-July7 7.5 8 35 8.5 9.3
June-July1.7 2.2 2.7 32 3.2 4
Mancos
Mancos, Nr April-July7.9 8 8.6 28 8.8 9.9
June-July1 1 1.6 16 1.9 3

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