March brought a mix of conditions to the Green River. The Upper portion of the basin had near average precipitation while the Yampa. Duchesne and Lower Green saw below average to well below average precipitation. Fortunately, temperatures were cool with daily maximums 3-7 Fahrenheit degrees below average and minimums 1 to 3 Fahrenheit degrees below average. This preserved much of the snowpack in the Yampa, Duchense and Lower Green basins where conditions are still above the April 1st average. In the Upper Basin, snowpack improved slightly from 90 percent on March first to 95 percent on April 1st.

Near average March precipitation brought the median basin forecast up to 85 percent in the Upper Green. However, dry soil conditions continue to influence the April through July Forecast in the Upper Green. While snowpack in near normal at many sites, modeled soil moisture is well below average with some regions in the 20 to 30 percent of the 30 year average. This accounts for the difference in the snow observations and the April through July runoff forecast.

March precipitation was only 70 percent average. Basin wide, snowpack remained 110 percent on April 1st. Key stations in portions of the Sierra Madre and Park Range increased snowpack. As a result, model guidance increased for some points and the median basin forecast is 125 percent. This increase is seen on the Elk River and Elkhead Creek, which are expected to see April through July volumes that are much above average.

Below average precipitation in March led to a reduction in forecasted volumes for points in the Duchesne River Basin. Continued cool temperatures and the potential for additional storms to impact the area during the first portion of April should keep runoff volumes near average to slightly above average.

The Lower Green Basin had the least March precipitation in the region. Snowpack dropped 15% from the March 1st but is still 120% of the April 1st average. Runoff volumes are anticipated to be near 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