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San Juan Water Supply Outlook, February 1, 2009


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

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the San Juan were below average last fall. This was most likely due to limited monsoonal precipitation over the summer months. Observed streamflow for the month of January was mostly below average for the San Juan.

-Snowpack/Precipitation...Snow water equivalents for the entire San Juan Basin on February 1st was 115 percent of average. Precipitation over the San Juan Basin for January was much below average with 55 percent. Seasonal precipitation for the San Juan Basin decreased to 105 percent of average.

-Short Term Precipitation Forecast...The forecast models through the end of the first week of February keep the San Juan Basin relatively dry.

-General Discussion...The CPC guidance has the possibility of above average precipitation and below normal temperatures for the second week of February. However, for February through April, CPC suggests a chance for below average preciptation. Due to the below average soil moiture in the upper basin this fall and the combination of current snowpack conditions and the CPC forecast, the median April-July forecast for the San Juan Basin is 110 percent of average.



*Median of forecasts within each basin.


San Juan Basin Conditions




* 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-July147250111355
Carracas, Nr April-July275440109665
Navajo Res, Archuleta, Nr April-July5808851131280
Farmington April-July83013401111850
Bluff, Nr April-July70013201071940
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July436011381
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July4975109108
Piedra
Arboles, Nr April-July142245107390
Los Pinos
Vallecito Res, Bayfield, Nr April-July152220107305
Animas
Durango April-July320475108670
Florida
Lemon Res, Durango, Nr April-July476411084
La Plata
Hesperus April-July17.12710840
Mancos
Mancos, Nr April-July14.43510656
South Ck
Lloyd's Rsvr Nr Monticello, Abv March-July0.61.3992.4

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 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 73.9 59 75.9 61
untitled San Juan
Navajo Res, Archuleta, Nr 1701.3 1264.7 74 1455.7 86
untitled Florida
Lemon Res, Durango, Nr 39.8 18.1 46 22.4 56
untitled
TOTAL 1866.5 1356.7 73 1554.0 83

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 1971-2000 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