After a somewhat dry start to the water year, December precipitation was much above average in the Upper Colorado, Gunnison and Dolores basins. This brought the seasonal precipitation to just above average in all basins and the January 1st snow water equivalent to much above average.

December precipitation was 170% of average in the Upper Colorado mainstem basin, which made up for a rather dry start to water year 2009. As of January 1st, the overall basin snow water equivalent was 125% of average. The snowpack is not uniform across the basin; the areas on the northern side of the basin, bordering the White and Yampa basins, have snow water equivalent percentages not quite as high as those in the areas on the southern side of the basin, which border the Gunnison basin. The Roaring Fork basin has the highest snow water equivalent with over 140% of average. Model soil moisture was near normal heading into the winter and December streamflow was also near normal. The April through July streamflow forecasts range between 92% and 116% of average at this time.

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the Gunnison was near to slightly below average in the fall. Observed streamflow for the month of December was near average for the Gunnison.

-Snowpack/Precipitation...As of January 1st, snowpack across the Gunnison was 130 percent of average. Precipitation over the Gunnison Basin for December was much above average with 210 percent. Seasonal average precipitation for the Gunnison increased to 115 percent.

-Short Term Precipitation Forecast...The forecast models through next week keep the Gunnison Basin relatively dry with near average temperatures.

-General Discussion...The current snowpack and statistical forecast suggest the April-July forecast of 105 to 110 percent of average. However, the ESP guidance suggests a forecast of near average due to slightly lower than average soil moisture. The CPC guidance continues to show the possibility of equal chances of above or below average precipitation for January through March across the Gunnison Basin.

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the Dolores were below average in the fall. This was most likely due to limited monsoonal precipitation during the summer months. Observed streamflow for the month of December was mostly below average for the Dolores.

-Snowpack/Precipitation...As of January 1st, snowpack across the Dolores is currently 145 percent of average. Precipitation over the Dolores Basin for December was much above average with 235 percent. Seasonal average precipitation for the Dolores Basin increased to 115 percent.

-Short Term Precipitation Forecast...The forecast models through next week keep the Dolores Basin relatively dry with near average temperatures.

-General Discussion...The current snowpack and statistical forecast suggest the April-July forecast of 115 to 120 percent of average. However, the ESP guidance suggests a forecast of around 110 percent of average due to lower than average soil moisture. The CPC guidance continues to show a possibility of below average precipitation for January through March across the Dolores 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