Modeled soil moisture continues to indicate much below and below average conditions for most of Green River Basin. (Click for November 1st image) This signal is incorporated in the ESP model guidance utilized by the CBRFC in generating our forecasts. At the time of this publication, seasonal precipitation is near normal for most of the region. Snowpack ranges from average to below average in the major tributaries of the Green River.

Despite above average December precipitation, the snow water equivalency in the Upper Green Basin remains below average. Low snowpack combined with the basin wide much below average soil moisture conditions resulted in ESP model guidance near 80% of the April through July average. While the antecedent soil moisture conditions will not change prior to runoff, there is ample time to accumulate snow in the upper basin. With this in mind, forecasts were kept at the upper bound of guidance levels for points in the Upper Green resulting in near-to and below-average volume predictions.

Currently, the Yampa and White River basins has the highest snowpack observations with most Snotel stations indicating average or above average values for January 1st. While soil simulations indicate drier than average conditions in portions of this region, headwater basins have near average conditions. Soil moisture deficits are not adversely effecting model guidance as much as in other regions. April through July forecast indicate near average runoff volumes for the Yampa and White basins.

December precipitation was 140 percent of average. This brought the Snowpack in the Duchesne Basin from 37 Percent of average on December 1st to 85 percent of average on January 1st. However, some Snotel stations located in the Eastern portion of the Uinta South slope report below average conditions. Soil conditions in the Duchesne are similar to he Upper Green with many basins indicating much below average conditions. Forecasts range near average on the headwaters of the basin to below average at downstream locations.

The Lower Green Basin has the lowest snowpack in the Green Basin as of January 1st. Despite this, forecasts range from near average to below 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