The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-February precipitation was near 80 percent of average in the upper Salt River Basin and 90 to 130 percent of average in the Verde River Basin.

February precipitation was 75 percent of average in the upper Salt Basin and near average in the Verde Basin.

Streamflow:
February streamflow was near 30 percent of median on the Salt River, 45 percent of median on the Tonto, and 75% of median on the Verde River.

Snow:
March 1st snowpack varied from 50 to 165 percent of average in the Verde River Basin, with the majority of sites reporting below average conditions. Snowpack in the upper Salt River Basin was generally less than 65 percent of average. In all areas snowpack was limited in areal coverage.

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 as more frequent precipitation events have occurred this winter.

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:
February storms affected primarily the upper Verde and western Arizona with near to above average precipitation for the month. The Salt River Basin experienced below average precipitation and entered the runoff season with drier soil moisture conditions compared to the Verde Basin. While a few sites reported above average snowpack conditions, most areas have recorded much below average snowpack. Streamflow in February was also well below median.

These conditions are somewhat consistent with La Nina climate conditions that currently exist. Below average precipitation and below median runoff are observed more frequently during La Nina events. March-May forecast volumes are for 20 percent of median in the Salt River Basin, near 35 percent of median in the Tonto Basin, and near 40 percent of median in the Verde Basin.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-February precipitation was ranged from near 30 to 50 percent of average.

February precipitation was ranged from near 30 to 45 percent of average.

Streamflow:
February streamflow was near 35 percent of median.

Snow:
March 1st snowpack conditions were near 50 percent of average in San Francisco Basin and 20 to 40 percent of average in the upper Gila Basin.

Upper Gila Basin Snow Plot.
San Francisco Basin Snow Plot

Soil Moisture:
Below average precipitation 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 March-May streamflow volumes in the Gila River Basin. These include below average seasonal precipitation and soil moisture, and much below average snowpack. The presence of La Nina climate conditions suggest drier than average conditions have a better chance of occuring through the forecast period. March-May forecast volumes range from 15 to 30 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-February precipitation ranged from near 60 percent of average in the headwater locations up to 125 percent of average near the basin outlet.

February precipitation ranged from 65 to 105 percent of average throughout most of the Little Colorado Basin.

Streamflow:
February streamflow on the Little Colorado at Lyman was near 45 percent of median.

Snow:
Basin snowpack conditions on February 1st were near 70 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 the headwater locations. Elsewhere soil moisture conditions were similar or wetter than last year entering the runoff period.

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:
The presence of La Nina climate conditions suggest below average precipitation into the spring. Below average seasonal precipitation exists over most of the Little Colorado Basin, with below average soil moisture conditions in the headwaters. Snowpack conditions changed little from February 1st to March 1st, and remain below average. March-May streamflow volumes are forecast to range from near 15 to 40 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