The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-December precipitation ranged from 75 to 110 percent of average in the Salt River Basin and 130 to 180 percent of average in the Verde River Basin.

December precipitation was 165 percent of average in the Salt River Basin, and near 200 percent in the Verde River Basin.

Streamflow:
December streamflow was near 65 percent of median on the Salt River and 190% of median on the Verde River.

Snow:
January 1st snowpack conditions were 200 percent of average in the Verde River Basin and 105 percent of average in the upper Salt River Basin.

Salt River Basin Snow Plot.
Verde River Basin Snow Plot.

Soil Moisture:
Below average precipitation during the late summer and fall resulted in below average modeled soil moisture states in the upper Salt River Basin. Wetter soil moisture conditions exist in the Verde Basin.

Climate Forecasts:
La Nina climate conditions suggest decreased chances for precipitation in this area. The La Nina influence was accounted for in generation of these forecasts.

Forecast Summary:
Despite above average seasonal precipitation, and above average January 1st snowpack, La Nina climate conditions suggest below average precipitation over the next few months. Forecasted runoff volumes represent this with lowest forecasts in the Salt River Basin where drier soil moisture conditions exist. January-May forecast volumes are near 90 percent of median in the Tonto and Verde River Basins and 65% of median in the Salt River Basin.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-December precipitation was near 55 percent of average.

December precipitation ranged from 80 to 110 percent of average.

Streamflow:
December streamflow ranged from 40 to 65 percent of median.

Snow:
Basin snowpack conditions were near 90 percent of average in San Francisco Basin and 60 percent of average in the upper Gila Basin.

Upper Gila Basin Snow Plot.
San Francisco Basin Snow Plot

Soil Moisture:
Below average precipitaiton has resulted in below average modeled soil moisture states.

Climate Forecasts:
La Nina climate conditions suggest decreased chances for precipitation in this area. The La Nina influence was accounted for in generation of these forecasts.

Forecast Summary:
Several conditions exist that support much below median January-May streamflow volumes in the Gila River Basin. Below average seasonal precipitation and soil moisture, much below average snowpack, and the presence of La Nina climate conditions resulted in January-May forecast volumes that range from 45 to 65 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-December precipitation varied significantly, from near 70 percent of average in the headwater locations up to 160 percent of average near the basin outlet.

December precipitation ranged from 140 to 230 percent of average.

Streamflow:
Minimal streamflow observations exist for December. December volume on the Little Colorado near Lyman was near 40 percent of median.

Snow:
Basin snowpack conditions were near 130 percent of average in the southern Headwaters.

Little Colorado Southern Headwaters Snow Plot
Central Mogollon Rim Snow Plot

Soil Moisture: Modeled soil moisture states varied throughout the Little Colorado. Below average seasonal precipitation resulted in below average soil moisture conditions in those areas. Elsewhere soil moisture conditions are similar or wetter than last year at this time.

Climate Forecasts:
La Nina climate conditions suggest decreased chances for precipitation in this area. The La Nina influence was accounted for in generation of these forecasts.

Forecast Summary:
Although snowpack was above average for January 1st, the wide range of seasonal precipitation indicate varying soil moisture conditions, with driest soils in eastern headwater areas. The presence of La Nina climate conditions suggest below average precipitation into the spring. January-May streamflow volumes are forecast to range from 35 to 85 percent of median.

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