The Northern Great Basin started the water year with an average October and a record dry November before experiencing a very wet December in the Weber, Six Creeks and Utah Lake Basins. The Bear River Basin is still struggling with below average numbers however it is too early in the accumulation season to predict a much below average year. As of January 4, weather guidance models are indicating several strong and wet storms for the Colorado Basin which will improve numbers in all basins in the short term. All basins are currently forecast in the below average catagory which ranges from 70%-89% of average.

December monthly precipitation was just above average at 112%. Snow water equivalent however were only 70% of average. Therefore, the April through July forecasts for Bear River basin vary from 51% at Stewart Dam to 84% in headwater basins above Evanston. Conditions look to be improving with a wet storm forecast for January 5-8th which should bring conditions closer to normal in the short term.

December precipitation was 132% of average over the Weber River Basin. Snow water equivalents were 83% of average. April through July forecasts ranged from 68% at Lost Creek to 85% at Wanship.

December precipitation was an impressive 156% of average for the Six Creeks Basin. This represents much above average for the month of December. Salt Lake City numbers ranked December 2007 as the 5th wettest December in 108 years of records. Snow water equivalents in the basin were variable however with and average SWE at 85%. This is due in part to an extremely dry November. Forecasts range from 72% of average at Parleys Canyon to 89% of average at Big Cottonwood Canyon.

December monthly precipitation was much above average over the Provo River Basin at 170%. Over the Utah Lake Basin however monthly precipitation was 145%. Snow water equivalent indexes for the Utah Lake Basin were 83% of average on January 1. After a very dry November, December helped improve an otherwise dry and poor start to this years forecast season. Forecasts range from 67% to 84% of the April-July 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