San Juan Water Supply Outlook, May 1, 2019

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by Greg Smith
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-July250 260 270 126 285 305
May-July198 210 220 122 235 255
Carracas, Nr April-July420 445 460 121 480 515
May-July315 340 355 118 375 410
Navajo Reservoir, Archuleta, Nr April-July810 870 930 127 970 1060
May-July580 640 700 124 740 830
Farmington April-July1280 1350 1420 129 1500 1650
May-July975 1050 1120 127 1200 1350
Bluff, Nr April-July1270 1350 1420 129 1500 1660
May-July950 1030 1100 129 1180 1340
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July58 63 67 124 71 76
May-July47 52 56 124 60 65
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July66 71 75 115 80 86
May-July53 58 62 115 67 73
Piedra
Arboles, Nr April-July265 280 295 140 310 330
May-July184 199 215 141 230 250
Los Pinos
Vallecito Reservoir, Bayfield, Nr April-July215 235 255 131 270 305
May-July180 200 220 129 235 270
Animas
Durango April-July460 500 535 129 555 685
May-July380 420 455 125 475 605
Florida
Lemon Reservoir, Durango, Nr April-July53 59 65 118 71 80
May-July47 53 59 120 65 74
La Plata
Hesperus April-July27 29 31 135 34 37
May-July22 24 26 143 29 32
Mancos
Mancos, Nr April-July29 31 34 110 38 41
May-July21 23 26 108 30 33

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 47.1 64 38 85.3 115 74.0 125.4
untitled San Juan
Navajo Reservoir, Archuleta, Nr 1116.7 82 66 1222.4 90 1361.0 1696.0
untitled Florida
Lemon Reservoir, Durango, Nr 12.5 52 32 21.5 89 24.1 39.8
untitled
TOTAL 1176.4 81 63 1329.2 91 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: Greg Smith