The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through December precipitation was near 70 percent of average in the Upper Colorado mainstem basin. The new water year started well with above average precipitation in October; however, November precipitation was below average and then December precipitation was just 35 percent of average.

Snow:
January 1st snow water equivalent was near 60 percent of average in the basin as a whole.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
December streamflow was near 110 percent of average.

Soil Moisture:
Modeled soil moisture states were above average heading into the winter.

Climate Forecasts:
La Nina climate conditions exist but these do not show a strong correlation with winter precipitation in the Upper Colorado mainstem basin, and therefore were not influential in the development of streamflow volume forecasts.

Forecast Summary:
Because of the below average November and, especially, December precipitation, as of January 1 both the seasonal precipitation and snow water equivalent are much below average at 70% and 60%, respectively. However, due to a very good runoff season last year and a wet October, above average soil moisture conditions existed in the Upper Colorado mainstem heading into the winter season. Therefore, current April through July streamflow volume forecasts range between 72 and 86 percent of average with a median value of 80 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through December precipitation was 75 percent of average in the Gunnison Basin. Above average precipitation occured in October. Dry conditions and much below average precipitation occurred in November.

December precipitation was also much below average, ranging from 30 percent of average in the East River watershed to 70% of average in the Uncompaghre watershed. The Gunnison basin-wide average for December was 50%.

Snow:
January 1st snow water equivalent was 65 percent of average in the Gunnison basin.

Gunnison Basin snow water equivalent plot

Streamflow:
December streamflow volumes ranged from 85 to 90 percent of average.

Soil Moisture:
Modeled soil moisture states were above average entering the winter season.

Climate Forecasts:
La Nina climate conditions exist but these do not show a strong correlation with winter precipitation in the Gunnison Basin, and therefore were not influential in the development of streamflow volume forecasts.

Forecast Summary:
A wet October was followed by drier condtions in November and December. Seasonal precipitation was near 75 percent of average as of January 1st, with a basin snow water equivalent value near 65 percent of average. High runoff in 2011 and a wet October resulted in above average soil moisture in the Gunnison Basin entering the winter season, impacting the forecasts. April-July streamflow runoff volumes are expected to range between 60 and 80 percent of the 1981-2010 average as of January 1st.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through December precipitation was 90 percent of average. Precipitation was above average in October and much below average in November.

December precipitation was near 90% of average.
Snow:
January 1st snow water equivalent was 85 percent of average in the Dolores Basin.

Dolores Basin snow water equivalent plot

Streamflow:
Many streamflow gages do not function well during the winter. December streamflow volumes in the Dolores River Basin have been estimated near 60% of average.

Soil Moisture:
Modeled soil moisture states were near to above average entering the winter season.

Climate Forecasts:
La Nina climate conditions exist but does not show a strong correlation with winter precipitation in the Dolores Basin. Therefore, it was not influential in the development of streamflow volume forecasts.

Forecast Summary:
Near to above average soil moisture existed in the Dolores River Basin entering the winter season. Above average precipitation occurred in October. Precipitation was much below average in November and near to below average in December. Seasonal precipitation was 90 percent of average on January 1st with snow water equivalent near 85 percent of average. April-July streamflow runoff volumes are expected to range from 70 to 80 percent of the 1981-2010 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 1981-2010 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