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San Juan Water Supply Outlook, June 1, 2011


Prepared by Tracy Cox
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

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through May precipitation was 100 percent of average, up 5 percent from last month. May precipitation was 145 percent of average, which was much above average.

Snow:
Current snow water equivalent for the entire basin is 115 percent, which is above average. The Animas basin is 135 percent and above Navajo is 100 percent. All three are up from the May 1st percentages.
--- Animas River Basin Snow Plot.
--- Above Navajo Basin Snow Plot.

Streamflow:
Streamflow for the entire San Juan Basin was much below average for May at 55%. Seasonal streamflow since October continued to be much below average at 60%, due to the much below average fall precipitation.

Soil Moisture:
Modeled soil moisture as of November 1st, 2010 was average to below average across the entire San Juan Basin.

Climate Forecasts:
The correlation of La Nina and April through July water volumes in the San Juan basin does suggest slightly drier than average December through May precipitation, but it did not influence the June forecast process.

Forecast Summary:
The April-July forecast volumes went up 5% from last month due to the much above average precipitation in May. Forecast volumes for June range between 69 and 102 percent of average with a median value of 80%.



* 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		50%
Exceedance
Volume		Percent
Average		10%
Exceedance
Volume
San Juan
Pagosa Springs April-July19420591230
June-July10011199135
Carracas, Nr April-July29033583390
June-July13818599240
Navajo Res, Archuleta, Nr April-July47554569620
June-July19026076335
Farmington April-July825945781050
June-July450570100675
Bluff, Nr April-July815950771110
June-July440575103735
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July39458553
June-July17.5249632
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July47547863
June-July24319140
Piedra
Arboles, Nr April-July15617476195
June-July628090101
Los Pinos
Vallecito Res, Bayfield, Nr April-July16017786195
June-July9311095128
Animas
Durango April-July410450102490
June-July280320128360
Florida
Lemon Res, Durango, Nr April-July37447652
June-July21288536
La Plata
Hesperus April-July16.118.37321
June-July5.887310.7
Mancos
Mancos, Nr April-July24278231
June-July8.8127315.9
South Ck
Lloyds Rsvr Nr Monticello, Abv March-July0.370.44320.56

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).

Reservoir Monthly Inflow Forecasts






San Juan End of Month Reservoir Contents (kaf)

Usable
Capacity		EOM
Contents		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Capacity
untitled Los Pinos
Vallecito Res, Bayfield, Nr 125.4 111.3 89 112.9 90
untitled San Juan
Navajo Res, Archuleta, Nr 1701.3 1427.8 84 1505.7 89
untitled Florida
Lemon Res, Durango, Nr 39.8 23.5 59 31.5 79
untitled
TOTAL 1866.5 1562.6 84 1650.1 88

Monthly Streamflows



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: Tracy Cox