The Green River Basin continues to have a wide distribution of water supply outlook conditions. Storm patterns favored the basin below Flaming Gorge helping to increase the forecast for those areas. Conditions upstream from Flaming Gorge continue to be below average.

January precipitation was above average at 115%. This brings the seasonal precipitation to near average conditions throughout many basins. However, the snowpack remains below average at 80% basin wide. The below average soil moisture states within the model continue to decrease objective guidance values. While NOAA's Climate Prediction Center indicates the potential for wetter than normal conditions over the next 30 days, shorter term weather models do not indicate significant precipitation in the Upper Green River Basin over the next 10 days. This influenced the decrease in the coordinated forecast for many points. Like December, monthly inflow to Flaming Gorge was near 50% of average.

Monthly precipitation for January was 145% of average in the Yampa River basin. Snowpack increased from 85% of basin average on January 1, to 110% on February 1. The Elk and Little Snake drainages show the best conditions with some stations near their seasonal maximum. Due to these improved conditions, forecasts increased throughout the Yampa and White Basins.

January precipitation was 165 % of average. The snowpack, which had high variability at the end of December, has increase to 120% of average as of February 1. All stations within the Uinta Basin have average to above average conditions. As a result, forecasts increased throughout the basin.

Similar to the Yampa and Duchesne, January precipitation has brought the snow pack from below average to above average conditions in the Lower Green. Basin wide, snow pack is 120% of average as of February 1. As one would expect, forecasts for the Eastern side of the Wasatch Plateau increased to a basin median of 105%.

It's worth noting that monthly precipitation reported by lower elevation gages in the San Rafael Swell region was below average for January. However, this area does not normally contribute substantial snow melt volume to forecast points within the Lower Green Basin.

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