Water Supply forecasts vary over the Green River basin from below normal values in the Upper Basin (points above Flaming Gorge) to near normal conditions in the other regions. This follows water year 2007 where observed flows through out the basin were below to much below average. However, it is still early in the snow accumulation season and there is ample time for conditions to change.

The Upper Green Basin stands out as having the lowest April through July Forecasts in the Colorado River Basin at this time. Despite December's above average precipitation, snow pack remains below average. After 5 years of below average flows, soils are very dry and influenced a lower forecast. This soil moisture deficit will persist through the forecast season. While climate forecasts indicate the chance for above average precipitation over the northern portion of the basin, this has yet to materialize.

Portions of the Yampa Basin are the only regions of the Green where forecasts are above 100% of average. This includes the Little Snake and Elk Rivers.

Snow pack in the Uinta Basin varies greatly. While some lower elevation stations are reporting near average snow water equivalent conditions, upper elevation sites remain below average. December's monthly precipitation was above average partly due to very high amounts at low elevations station that do not normally recieve significant precipitation. Meteorological models indicate the western portion of the basin will receive significant precipitation the second weekend of January that will improve the snow pack in the short term.

As in the Duchesne Basin, large amounts of precipitation at lower elevation gages pushed the monthly totals near 200 percent of average. Runoff in the Lower Green Basin, points in the Price and San Rafael drainages, is expected to be near average. Some snow sites in the along the Wasatch Plateau are above average as a result of favorable storm direction during events in early December. Slightly to the east, stations report near average conditions. As in the Western Uinta Basin, there exists the potential for significant accumulation with the storms arriving in early January.

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