The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation ranged from near 100 to 115 percent of average across the Salt and Verde River Basins.

March precipitation ranged from near 70 to 90 percent of average.

Streamflow:
Precipitation combined with snow melt resulted in above median streamflow in March. Streamflow volumes were near 115 percent of median on the Salt River, 430 percent on the Tonto River, and 270 percent of median on the Verde River.

Snow:
Significant snow remains at higher elevations in the Salt and Verde Basins. Basin snowpack was near 300 percent of average in the Verde Basin and 230 percent of average in the Salt Basin on April 1st. Although area coverage of snowpack has been decreasing, some locations that are typically void of snow on April 1st still contain up to 10 inches of water in the snowpack.

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

Soil Moisture:
Dry soils existed prior to the winter season. Soil moisture increased at lower elevations with rainfall during the winter. Areas with persistent snowpack throughout the winter maintained dry soils prior to the onset of snow melt.

Climate Forecasts:
El Nino climate conditions are expected to persist through the spring. The El Nino influence was accounted for in generation of forecasts this season. While El Nino climate conditions suggest increased chances for precipitation during the winter and early spring months, the relationship between El Nino and precipitation is much weaker during the April-June period.

Forecast Summary:
A significant snowpack exists at high elevations of the Salt and Verde Basins for this time of year. Above average runoff is anticipated over the next 2 months, however limited areal coverage of the snowpack combined with dry soils that existed prior to the onset of snow melt may reduce volumes. April through May streamflow volumes from 180 to 250 percent of median are expected.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation is near 110 percent of average in upper Gila River Basin.
March precipitation ranged from 100 to 110 percent of average in the upper Gila River Basin.

Streamflow:
March streamflow volumes were 200 to 280 percent of median in the San Francisco and upper Gila River Basin due to rainfall and snow melt during the month.

Snow:
Upper Gila Basin snowpack was near 240 percent of average on April 1st. The largest amount of water in the snowpack was at highest elevations, but snowcover at these elevations is limited in areal extent.

Upper Gila Basin Snow Plot.
San Francisco Basin Snow Plot

Soil Moisture:
Dry soils existed prior to the winter season. Soil moisture increased at lower elevations with rainfall during the winter. Areas with persistent snowpack throughout the winter maintained dry soils prior to the onset of snow melt.

Climate Forecasts:
El Nino climate conditions are expected to persist through the spring. The El Nino influence was accounted for in generation of forecasts this season. While El Nino climate conditions suggest increased chances for preciptation during the winter and early spring months, the relationship between El Nino and precipitation is much weaker during the April-June period.

Forecast Summary:
Above average snowpack exists in the upper Gila Basin particularly at highest elevations above 9000 feet. Above average runoff is anticipated over the next 2 months, however limited areal coverage of the snowpack combined with dry soils that existed prior to the onset of snow melt may reduce volumes. April through May streamflow volumes are expected to range mostly between 200 to 300 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-March precipitation ranged from 80 to 120 percent of average throughout the Little Colorado Basin.

March precipitation ranged from 50 to 85 percent of average. Headwater locations were near 90 percent of average.

Streamflow:
Although observed streamflow data was limited, March streamflow volumes in the Little Colorado were below median in the higher elevations. Below average precipitation and below average temperatures for the month reduced snow melt.

Snow:
Basin snowpack conditions ranged frome 180 to 300 percent of average on April 1st in the Southern Headwaters of the Little Colorado Basin.

Little Colorado Southern Headwaters Snow Plot
Central Mogollon Rim Snow Plot

Soil Moisture: Dry soils existed prior to the winter season. Soil moisture increased at lower elevations with rainfall during the winter. Areas with persistent snowpack throughout the winter maintained dry soils prior to the onset of snow melt.

Climate Forecasts:
El Nino climate conditions are expected to persist through the spring. The El Nino influence was accounted for in generation of forecasts this season. While El Nino climate conditions suggest increased chances for preciptation during the winter and early spring months, the relationship between El Nino and precipitation is much weaker during the April-June period.

Forecast Summary:
Significant snowpack exists in higher elevations of the Little Colorado drainage for this time of year. While above median volumes are expected over the next 2-3 months, dry soils that existed under the snowpack prior to the onset of snow melt could act to reduce snow melt runoff volumes. April through May streamflow volumes from near 200 to 500 percent of median are expected.

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