The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 95 percent of average in the Upper Green basin as a whole. March precipitation was 50 percent of average.

Snow:
April 1st snow water equivalent was 85 percent of average in the basin as a whole. Low and mid elevation snowmelt occurred due to much above average temperatures in March.
--- Upper Green basin snow water equivalent plot.

Streamflow:
March 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:
March precipitation was much below average; however, seasonal precipitation in the Upper Green remains near average as a result of above average precipitation in months other than December and March. As a result of early snowmelt and much below average precipitation during March, the snow water equivalent decreased from near average to below average. As a result, current April through July streamflow volume forecasts in the headwaters of the Upper Green have decreased by 5 to 10 percent while forecasts for basins located in the Wyoming range (Ham's Fork) or the North Slope of the Uintas decreased by 15 to 20 percent. Forecasts now range between 60 and 99 percent of average with a median value of 86 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 70 percent of average in the Yampa/White basin. March precipitation was near 30 percent of average. This is the driest March on record for many of the SNOTEL sites in the basin.

Snow:
April 1st snow water equivalent was 50 percent of average in the basin. Significant snowmelt occurred at low and mid elevations due to much above average temperatures in March.
--- Yampa basin snow water equivalent plot.

Streamflow:
March streamflow was 140 percent of average as a result of the early snowmelt.

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:
Due to much below average March precipitation, seasonal precipitation is now below average in the Yampa/White. Significant snowmelt occurred during March due to the warm and dry conditions. By April 1st, the snow water equivalent had been reduced from 80 percent of average on March 1st to near 50 percent of average. Many of the SNOTEL locations have record or near record low snow water equivalent for this time of year. As a result of the unusual dry and warm conditions in March, current April through July streamflow volume forecasts have drastically decreased by 25 to 40 percent with the greatest decreases occurring in the Elkhead and Little Snake basins. Forecasts now range between 38 and 59 percent of average with a median value of 54 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 80 percent of average in the Duchesne basin. March precipitation was 60 percent of average.

Snow:
April 1st snow water equivalent was 55 percent of average in the basin. Low and mid elevation snowmelt occurred due to much above average temperatures in March.
--- Duchesne basin snow water equivalent plot.

Streamflow:
March streamflow was near 120 percent of average over the basin.

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:
March precipitation was much below average in the Duchesne and seasonal precipitation still remains below average. Significant snowmelt occurred below 9000 feet due to the warm and dry conditions in March. As of April 1st, the snow water equivalent over the basin as a whole had been reduced from 70 percent of average on March 1st to 50 percent of average. As a result, current April through July streamflow volume forecasts decreased by 5 to 10 percent in the higher elevation basins and by 20 to 30 percent in lower elevation basins such as Currant Creek, Strawberry, and Big Brush drainages. Forecasts now range between 29 and 78 percent of average with a median value of 62 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 80 percent of average in the Lower Green basin. March precipitation was 45 percent of average.

Snow:
April 1st snow water equivalent was 40 percent of average in the basin. Significant snowmelt occurred due to much above average temperatures in March.
--- Lower Green basin snow water equivalent plot.

Streamflow:
March streamflow was near 90 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:
March precipitation was much below average in the Lower Green and seasonal precipitation remains below average. As a result of the snowmelt during March, the snow water equivalent is now much below average and has been reduced from 65 percent on March 1st to 40 percent of average. As a result, current April through July streamflow volume forecasts have decreased by 10 to 20 percent and now range between 39 and 59 percent of average with a median value of 53 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