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.Lake Powell Water Supply Outlook, February 1, 2012

Lake Powell Water Supply Outlook, February 1, 2012


Prepared by Alcorn
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Lake Powell Sub-Basin Summaries




*Median of forecasts within each basin.





*Median of forecasts within each basin.







*Median of forecasts within each basin.




Upper Green Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was 100 percent of average in the Upper Green basin. January precipitation was 125 percent of average.

Snow:
February 1st snow water equivalent was 100 percent of average in the basin.
--- Upper Green basin snow water equivalent plot.

Streamflow:
January streamflow was near 110 percent of average.

Soil Moisture:
Modeled soil moisture states indicated near average to above average soil moisture conditions last fall prior to snow accumulation.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between La Nina conditions and winter precipitation in the Upper Green basin.

Forecast Summary:
Seasonal precipitation in the Upper Green remains near average as a result of above average and much above average precipitation in October, November, and January. Snow water equivalent has increased from below average on January 1 to near average due to the above average precipitation in January. It is also important to note that fall soil moisture conditions were near to above average. As a result, current April through July streamflow volume forecasts increased by 15 to 20 percent and range between 74 and 100 percent of average with a median value of 94 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Yampa/White Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was 70 percent of average in the Yampa/White basin. January precipitation was near 60 percent of average.

Snow:
February 1st snow water equivalent was 65 percent of average in the basin.
--- Yampa basin snow water equivalent plot.

Streamflow:
January streamflow ranged between 110 and 120 percent of average.

Soil Moisture:
Modeled soil moisture states indicated above average to much above average soil moisture conditions last fall prior to snow accumulation.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Yampa/White basin.

Forecast Summary:
January precipitation was much below average in the Yampa/White basins. As a result of much below average conditions for both December and January, both seasonal precipitation and snow water equivalent are much below average. It is also important to note that fall soil moisture conditions were above to much above average. As a result of another below average month, current April through July streamflow volume forecasts have decreased by 5 to 10 percent and now range between 62 and 79 percent of average with a median value of 70 percent. Forecasts are slightly higher than current snow conditions might suggest due to wet antecedent conditions.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Duchesne Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was 85 percent of average in the Duchesne basin. January precipitation was 70 percent of average.

Snow:
February 1st snow water equivalent was 65 percent of average in the basin.
--- Duchesne basin snow water equivalent plot.

Streamflow:
December streamflow was 115 percent of average.

Soil Moisture:
Modeled soil moisture states indicated much above average soil moisture conditions last fall prior to snow accumulation.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Duchesne basin.

Forecast Summary:
Seasonal precipitation in the Duchesne is below average as a result of much below average and below average conditions in December and January. Snow water equivalent is also much below average for the majority of the basin. However, it is important to note that fall precipitation and soil moisture conditions were much above average. Wet antecedent conditions are resulting in somewhat higher forecasts for the Whiterocks and Uinta river basins. As a result, current April through July streamflow volume forecasts have decreased by 5 to 10 percent and range between 54 and 93 percent of average with a median value of 69 percent. Forecasts are slightly higher than current snow conditions might suggest due to wet antecedent conditions.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Lower Green Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was 80 percent of average in the Lower Green basin. January precipitation was 85 percent of average.

Snow:
February 1st snow water equivalent was 55 percent of average in the basin.
--- Lower Green basin snow water equivalent plot.

Streamflow:
January streamflow ranged from 120 to 130 percent of average.

Soil Moisture:
Modeled soil moisture states indicated near average to above average soil moisture conditions last fall prior to snow accumulation.

Climate Forecasts:
Climate forecasts were not a factor in the forecasts because there is not a strong correlation between La Nina conditions and winter precipitation in the Lower Green basin.

Forecast Summary:
Seasonal precipitation is below average and snow water equivalent is much below average in the Lower Green due to below average monthly precipitation in November, December, and January. It is also important to note the fall soil moisture conditions were near to above average. As a result, current April through July streamflow volume forecasts remain similar to January 1 and range between 56 and 75 percent of average with a median value of 65 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Upper Colorado Mainstem Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was near 75 percent of average in the Upper Colorado mainstem basin. Above average precipitation occured in October but was followed by two months of much below average precipitation in November and December. January precipitation was near normal at 95 percent of average.

Snow:
February 1st snow water equivalent was near 70 percent of average in the basin as a whole. While it is still below average, it is an improvement from the 60 percent of average observed on January 1st.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
January streamflow was near 110 percent of average.

Soil Moisture:
Modeled soil moisture states were above average heading into the winter.

Climate Forecasts:
La Nina climate conditions exist but these do not show a strong correlation with winter precipitation in the Upper Colorado mainstem basin, and therefore were not influential in the development of streamflow volume forecasts.

Forecast Summary:
Because of the below average November and, especially, December precipitation, as of February 1 both the seasonal precipitation and snow water equivalent are below average at 75% and 70%, respectively. However, due to a very good runoff season last year and a wet October, above average soil moisture conditions existed in the Upper Colorado mainstem heading into the winter season. As a result of near normal January precipitation most forecasts are unchanged from last month. Current April through July streamflow volume forecasts range between 70 and 86 percent of average with a median value of 80 percent.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Gunnison Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was 85 percent of average in the Gunnison Basin. Above average precipitation occured in October. Dry conditions and much below average precipitation occurred in November and December.

January precipitation was near to above average in upper Gunnison and East River Basins, with near to slightly below average precipitation elsewhere.

Snow:
February 1st snow water equivalent was 75 percent of average in the Gunnison basin.

Gunnison Basin snow water equivalent plot

Streamflow:
January streamflow volumes ranged from 70 to 90 percent of average.

Soil Moisture:
Modeled soil moisture states were above average entering the winter season.

Climate Forecasts:
La Nina climate conditions exist but these do not show a strong correlation with winter precipitation in the Gunnison Basin, and therefore were not influential in the development of streamflow volume forecasts.

Forecast Summary:
A wet October was followed by drier condtions in November and December. January precipitation was near or above average at most locations. Seasonal precipitation was near 85 percent of average as of February 1st, with a basin snow water equivalent value near 75 percent of average. High runoff in 2011 and a wet October resulted in above average soil moisture in the Gunnison Basin entering the winter season. April-July streamflow runoff volumes changed little from those issued January 1st and are expected to range between 60 and 80 percent of the 1981-2010 average.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Dolores Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was near 90 percent of average. Precipitation was above average in October, much below average in November, and near to below average in December.

January precipitation ranged from 80 to 95 percent of average.

Snow:
February 1st snow water equivalent was 75 percent of average in the Dolores Basin.

Dolores Basin snow water equivalent plot

Streamflow:
January streamflow volumes in the Dolores River Basin were near 65 percent of average.

Soil Moisture:
Modeled soil moisture states were near average entering the winter season.

Climate Forecasts:
La Nina climate conditions exist but does not show a strong correlation with winter precipitation in the Dolores Basin. Therefore, it was not influential in the development of streamflow volume forecasts.

Forecast Summary:
Near average soil moisture existed in the Dolores River Basin entering the winter season. Seasonal precipitation was near 90 percent of average on February 1st, with October the only month with above average precipitation. February 1st snow water equivalent was 75 percent of average in the Dolores Basin. April-July streamflow runoff volumes are expected to range from 65 to 80 percent of the 1981-2010 average.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

San Juan Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through January precipitation was near average. October was wet, while November through December experienced drier than average conditions.

January was dry with a basin average precipitation near 65 percent.

Snow:
February 1st snow water equivalent for the entire basin was near 75% of average.
Animas River Basin Snow Plot.

San Juan Basin (above Navajo Reservoir) Snow Plot.

Streamflow:
Streamflow volumes for January ranged from 60% of average at the Basin outlet to near 90% of average at higher elevations.

Soil Moisture:
Modeled soil moisture has been updated since January 1st and 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 exist and a weak to moderate La Nina episode is anticipated to continue through the winter season. The La Nina climate condition suggests drier than average conditions possible over the San Juan Basin. The La Nina climate condtion was considered when developing the forecasts.

Forecast Summary:
Seasonal precipitation is near average due to a wet October. Snowpack conditions are below average due to drier weather November through January. Soil Moisture varied entering the winter season, with near or slightly above average conditions in high elevations in the northern headwaters, and below average conditions elsewhere. La Nina climate conditions suggest below average precipitation is possible over the San Juan Basin through spring. April-July runoff volumes are expected to range from 75 to 90 percent of the 1981-2010 average.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

















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



















Monthly Streamflows

















Precipitation Maps