November modeled soil moisture indicated 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 above average to below average in the major tributaries of the Green River.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Upper Green Basin. Observed streamflow for the month of February was 75 percent of average.

-Snowpack/Precipitation...In the Upper Green Basin, February precipitation was 75 percent of average. The basinwide to date snowpack condition is 85 percent of average with individual Snotel stations ranging from 48 to 102 percent of average.

-General Discussion...National Weather Service models suggest near to slightly above normal precipitation for the next 7-10 days. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below precipitation. The 90 Day CPC guidance is for below normal precipitation. The antecedent soil moisture conditions will not change prior to runoff. April through July forecast indicate below average to average runoff volumes.

-Model Soil Moisture/Observed Streamflow...While soil moisture indicate drier than average Fall conditions in portions of this region, headwater basins had near average conditions. Therefore, soil moisture deficits are not adversely effecting model guidance as much as in other regions. Observed streamflow for the month of February was above average.

-Snowpack/Precipitation...Currently, the Yampa and White River basin has the highest snowpack conditions within the Green, with 75 percent of the Snotel stations having values greater than 110 percent of average on March 1st. February precipitation was only 85 percent of average.

-General Discussion...National Weather Service models suggest near to slightly above normal precipitation for the next 7-10 days. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below precipitation. The 90 Day CPC guidance is for below normal precipitation. April through July forecast runoff volumes for the Yampa and White Basins ranged from average to above average.

-Model Soil Moisture/Observed Streamflow...Fall soil conditions in the Duchesne were similar to the Upper Green with many basins indicating much below average conditions. Observed streamflow for the month of February was below average.

-Snowpack/Precipitation...The snowpack condition in the Duchesne Basin on March 1st is same as on the 1st of the last two months (January and February) at 85 percent of average, with 78 percent of the Snotel stations located in in the basin reporting below average conditions. February precipitation was 95 percent of average.

-General Discussion...National Weather Service models suggest near to slightly above normal precipitation for the next 7-10 days. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below precipitation. The 90 Day CPC guidance is for below normal precipitation. Forecasts range below average on the headwaters of the basin to much below average at downstream locations.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Lower Green Basin. Observed streamflow for the month of February was below average.

-Snowpack/Precipitation...The Lower Green Basin snowpack condition was 80 percent of average on March 1st. February precipitation was 95 percent of average.

-General Discussion...National Weather Service models suggest near to slightly above normal precipitation for the next 7-10 days. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below precipitation. The 90 Day CPC guidance is for below normal precipitation. Forecasts at this time, are now all 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