The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation was near 70 percent of average in the upper Salt River Basin and 80 to 105 percent in Verde River Basins.

March precipitation was near 20 to 30 percent of average in the upper Salt and Verde River Basins.

Streamflow:
March streamflow was near 20 percent of median on the Salt River, 40 percent of median on the Tonto, and near median on the Verde River.

Snow:
The snowpack has been all but depleted with only isolated pockets of snow remaining in high elevation protected areas.

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

Soil Moisture:
Soil moisture conditions were below average at the onset of the runoff period due to dry conditions late last summer and fall. The wettest soils existed in the Verde River Basin, however these have become drier as the snow has melted and below average precipitation occurred in March.

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:
Below average precipitation occurred in March while the remaining snow melted. Seasonal precipitation was near average in headwater sections of the Verde Basin, but much below average elsewhere. Runoff conditions over the past 3 months in the Verde were closer to median values compared to the upper Salt where drier conditions have been more persistent.

These conditions are consistent with La Nina climate conditions that currently exist. Below average precipitation and below median runoff are observed more frequently during La Nina events. April-May forecast volumes range from 15 to 45 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation ranged from 15 to 60 percent of average.

March precipitation was generally less than 10 percent of average.

Streamflow:
February streamflow ranged from 15 to 20 percent of median.

Snow:
The snowpack has been depleted in the Gila River Basin with only isolated pockets of snow at higher elevations in the San Francisco Basin.

Upper Gila Basin Snow Plot.
San Francisco Basin Snow Plot

Soil Moisture:
Very dry conditions in the Gila Basin for several months has resulted in below average soil moisture conditions.

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 Gila River Basin has experienced below average precipitation dating back to last summer. Runoff conditions have subsequently been much below median throughout the winter and early spring. These conditions have been consistent with La Nina climate condtions that currently exist. Although La Nina conditions are expected to weaken into early summer, climate outlooks suggest below average precpitation into early summer. April-May forecast volumes range from 20 to 35 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation ranged from near 60 percent of average in the headwater locations up to 120 percent of average near the basin outlet.

March precipitation ranged from 10 to 50 percent of average throughout most of the Little Colorado Basin.

Streamflow:
March streamflow on the Little Colorado at Lyman was near 20 percent of median.

Snow:
Snowpack has been depleted in the Little Colorado Basin. Only isolated pockets of snow remain at highest elevations.

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, but have since dried due to below average precipitation.

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 through the spring. Below average seasonal precipitation exists over most of the Little Colorado Basin, with below average soil moisture conditions in the headwaters. Snowpack was below average for the season and has since melted off. April-May streamflow volumes are forecast to range from near 5 to 20 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