The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 125 percent of average in the Upper Green basin. March precipitation was 105 percent of average in the basin as a whole; however, portions of the basin received much above average precipitation such as the headwaters of the mainstem of the Green River which received near 150 percent of average.

Snow:
April 1st snow water equivalent was 120 percent of average in the basin.
--- Upper Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 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 La Nina conditions and winter precipitation in the Upper Green basin.

Forecast Summary:
With the addition of another month of near average precipitation and localized areas with much above average precipitation, the seasonal precipitation and snow water equivalent still remain above average for the Upper Green. As a result of the current conditions, the April through July streamflow volume forecasts increased by approximately 5 to 10 percent from the March 1 forecasts. Current forecasts range between 100 and 140 percent of average with a median value of 114 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 130 percent of average in the Yampa/White basin. March precipitation was 120 percent of average in the basin as a whole.

Snow:
April 1st snow water equivalent was 130 percent of average in the basin.
--- Yampa basin snow water equivalent plot.

Streamflow:
March streamflow was near 100 percent of average.

Soil Moisture:
Modeled soil moisture states were near average heading into the winter for the Yampa, Little Snake,and White River basins.

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:
With the addition of above average precipitation in March, the seasonal precipitation and current snow water equivalent remain much above average. It is also important to note that many of the snotel locations have record or near record snow water equivlent for this time of the year. As a result of the current conditions, the April through July streamflow volume forecasts have increased by approximately 10 to 20 percent. Current forecasts range between 128 and 162 percent of average with a median value of 151 percent. Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 155 percent of average in the Duchesne basin. March precipitation was 85 percent of average the basin as a whole; however, portions of the basin received much below average precipitation such as the headwaters of Ashley Creek, Big Brush, and Whiterocks.

Snow:
April 1st snow water equivalent was 145 percent of average in the basin.
--- Duchesne basin snow water equivalent plot.

Streamflow:
March streamflow was 90 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 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 and current snow water equivalent still remain much above average in spite of the below average March precipitation. As a result of the current conditions, the majority of the April through July streamflow volume forecasts did not change from March. However, forecasts for the Duchesne, Strawberry, and Rock Creek rivers have increased by approximately 5 to 10 percent while forecasts for Ashley Creek, Big Brush, and Whiterocks have decreased by approximately 5 to 10 percent as a result of the much below average March precipitation. Current forecasts range between 106 and 193 percent of average with a median value of 153 percent. Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 160 percent of average in the Lower Green basin. March precipitation was 90 percent of average.

Snow:
April 1st snow water equivalent was 120 percent of average in the basin as a whole.
--- Lower Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 80 percent of average.

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

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:
With the addition of near average precipitation in March, the seasonal precipitation and current snow water equivalent remain much above average and above average, respectively. As a result of the current conditions, the April through July streamflow volume forecasts are similar to the March forecasts with the exception of Green River at Green River, UT which increase by 11 percent. Current forecasts range between 121 and 151 percent of average with a median value of 141 percent.

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 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.

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