The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 70 percent of average in the Upper Green basin. March precipitation was 80 percent of average.

Snow:
April 1st snow water equivalent was near 60 percent of average in the basin as a whole.
--- Upper Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 85 percent of average.

Soil Moisture:
Modeled soil moisture states ranged from below average to near average heading into the winter.

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

Forecast Summary:
Due to below average seasonal precipitation to date and much below average April 1st snow water equivalent values the April through July streamflow volume forecasts are much below average at this time. These forecasts have dropped slightly and now range between 38 and 66 percent of average, with a median value of 50 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 80 percent of average in the Yampa/White basin. March precipitation was 75 percent of average.

Snow:
April 1st snow water equivalent was 75 percent of average in the basin as a whole.
--- Yampa basin snow water equivalent plot.

Streamflow:
March streamflow was near 60 percent of average.

Soil Moisture:
Modeled soil moisture states were near average heading into the winter for the Little Snake and White River basins. Modeled states ranged from below average to near average heading into winter for the Yampa basin.

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

Forecast Summary:
Due to below average seasonal precipitation to date and below average April 1st snow water equivalent values the April through July streamflow volume forecasts are below average at this time. These forecasts have dropped slightly and now range between 54 and 76 percent of average, with a median value of 70 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 70 percent of average in the Duchesne basin. March precipitation was 75 percent of average.

Snow:
April 1st snow water equivalent was 70 percent of average in the basin as a whole.
--- Duchesne basin snow water equivalent plot.

Streamflow:
March streamflow was 85 percent of average.

Soil Moisture:
Modeled soil moisture states were much below average to below average heading into the winter.

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

Forecast Summary:
Due to below average seasonal precipitation to date and below average April 1st snow water equivalent values the April through July streamflow volume forecasts are much below average at this time. These forecasts have dropped slightly and now range between 45 and 75 percent of average, with a median value of 65 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 95 percent of average in the headwaters of the Lower Green basin. March precipitation was 100 percent of average.

Snow:
April 1st snow water equivalent was 70 percent of average in the basin as a whole. The Price and San Rafael headwaters did not receive as much snow as those further to the south.
--- Price basin snow water equivalent plot.

Streamflow:
March streamflow was near 80 percent of average.

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

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

Forecast Summary:
Due to the below average April 1st snow water equivalent values, and the much below average soil moisture heading into winter the April through July streamflow volume forecasts are much below average at this time. These forecasts have dropped slightly and now range between 44 and 60 percent of average, with a median value of 50 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was near 80 percent of average in the Upper Colorado mainstem basin. March precipitation was near 70 percent of average.

Snow:
April 1st snow water equivalent was near 75 percent of average in the basin as a whole.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
March streamflow was near 80 percent of average.

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

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between El Nino conditions and winter precipitation in the Upper Colorado mainstem basin.

Forecast Summary:
As a result of below average March precipitation, many of the April through July streamflow volume forecasts decreased by 5-10% from last month. Due to below average seasonal precipitation and snow water equivalent, these forecasts range between 45 and 80 percent of average with a median value of 70 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 95 percent of average in the Gunnison basin. March precipitation was 95 percent of average.

Snow:
April 1st snow water equivalent was 95 percent of average in the Gunnison basin.
--- Gunnison basin snow water equivalent plot

Streamflow:
March streamflow was 80 percent of average.

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

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between El Nino conditions and winter precipitation in the Gunnison basin.

Forecast Summary:
March precipitation throughout the Gunnison basin was 95% of average. April 1st snow water equivalent for the Gunnison continued to be near average with 95%. Therefore, the April through July volume forecast did not change much from last month. The Gunnison forecasts now range between 74 and 91 percent of average, with a median value of 80 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 105 percent of average in the entire Dolores basin. March precipitation was 115 percent of average.

Snow:
April 1st snow water equivalent was 105 percent of average in the Dolores basin.
--- Dolores basin snow water equivalent plot

Streamflow:
March streamflow was 35 percent of average.

Soil Moisture:
Modeled soil moisture states were below to much below average heading into the winter.

Climate Forecasts:
The correlation of El Nino and April through July water volumes in the Dolores basin is so small that it did not influence the forecast process.

Forecast Summary:
Although March precipitation throughout the Dolores Basin was 115% of average, March precipitation in the upper portions of the Dolores basin was below to much below average. Seasonal October through March precipitation in the upper portions of the Dolores basin was average to below average. Therefore, the April through July volume forecast was lowered slightly by 5%. The Dolores forecasts now range between 81 and 87 percent of average, with a median value of 80 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation amounts dropped from last month, but remained near average at 105%.
March precipitation was below average with 70%.

Snow:
Current snow water equivalent for the entire basin dropped from last month and is now 100%, which is near average. The Animas basin snow water equivalent dropped as well and is now 95% percent of average. The above Navajo snow water equivalent dropped also from last month and is average with 100%.
--- Animas River Basin Snow Plot.
--- Above Navajo Basin Snow Plot.

Streamflow:
Streamflow for the entire San Juan Basin was below average in March. Seasonal streamflow since October was 55% due to the much below average summer through fall precipitation.

Soil Moisture:
Modeled soil moisture as of November 1st, 2009 was below to much below average.

Climate Forecasts:
The correlation of El Nino and April through July water volumes in the San Juan basin is so small that it did not influence the forecast process.

Forecast Summary:
Current snowpack conditions decreased slightly in March, but remained near average. Monthly precipitation for March was only 70% of average basin wide. This helped drive the San Juan Water Supply April-July forecast down 10% from the previous month to 90% of average.

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).

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.

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