New 1981-2010 Averages being used this year.
Note: This publication is currently undergoing major revisions. The current publication will be replaced with a new publication based on stakeholder requirements and scientific advances. We expect to begin sharing details on this soon. If you have input on content, format, or publication frequency at any time, please contact us at cbrfc.webmasters@noaa.gov.San Juan Water Supply Outlook, June 1, 2012

San Juan Water Supply Outlook, June 1, 2012


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

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through May precipitation was between 65 to 85 percent of average at most locations in the San Juan Basin.

May was the third consecutive month with very dry conditions. Precipitation in May ranged from 0 to near 55 percent of average over most of the San Juan Basin. The Basin average from the month of May was 25% of average.

Snow:
Snow melted off at measuring sites by early June. The warm and dry spring caused snow to melt out a full 4 to 6 weeks early at many locations.

Animas River Basin Snow Plot.

San Juan Basin (above Navajo Reservoir) Snow Plot.

Streamflow:
Streamflow volumes were much below average in May due to the lack of snow. Runoff volumes in May ranged from 40 to 60 percent of average.

Soil Moisture:
Modeled soil moisture was near to above average at highest elevations entering the winter season. Below average soil moisture conditions existed over the southern half of the basin and in tributaries further downstream.

Climate Forecasts:
La Nina climate conditions existed through the winter months. The La Nina climate condition suggests drier than average conditions possible over the San Juan Basin. The La Nina climate condition was considered when developing the forecasts.

Forecast Summary:
The 2012 season was defined by very dry and warm conditions that persisted throughout the spring that resulted in a very early snow melt. At times during the spring the snow pack was at record or near record low levels due to the dry and warm conditions. Runoff volume forecasts were reduced as the season progressed and the dry conditions persisted. Forecasts have been reduced slightly from those issued in early May and some are in the bottom 5 of the historical record. April-July runoff volumes are expected to range from 35 to 55 percent of the 1981-2010 average. June-July runoff volumes volumes are expected to range from near 10 to 30 percent of average.



* 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-July10911453132
June-July17252640
Carracas, Nr April-July15517947220
June-July16402581
Navajo Res, Archuleta, Nr April-July30033045385
June-July205017.2106
Farmington April-July45047042490
June-July355010.670
Bluff, Nr April-July37540537455
June-July11.9429.291
Rio Blanco
Pagosa Springs, Nr, Blanco Dam, Blo April-July22254632
June-July252211.6
Navajo
Chromo, Nr, Oso Div Dam, Blo April-July29324936
June-July5.182711.8
Piedra
Arboles, Nr April-July9010650121
June-July4.7202735
Los Pinos
Vallecito Res, Bayfield, Nr April-July9610655117
June-July17.3282839
Animas
Durango April-July20023055255
June-July38653092
Florida
Lemon Res, Durango, Nr April-July30336038
June-July3.87.32611.9
La Plata
Hesperus April-July10.311.14812.2
June-July1.52243.1
Mancos
Mancos, Nr April-July11.912.94214.4
June-July1.52.5244

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 125.4 123.7 99 111.3 89
untitled San Juan
Navajo Res, Archuleta, Nr 1701.3 1302.7 77 1427.8 84
untitled Florida
Lemon Res, Durango, Nr 39.8 31.6 79 23.5 59
untitled
TOTAL 1866.5 1458.0 78 1562.6 84

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: Greg Smith