The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-January precipitation is near 120 percent of average in the Salt River Basin and 130 percent in the Verde River Basin.

January precipitation was significant due to heavy rainfall during the second half of the month. January precipitation ranged from 200 to 400 percent of average over most of the Salt and Verde Basins.

Streamflow:
Significant Runoff occured the third week of January due to heavy rainfall. January streamflow volumes varied widely and included 850 percent of median on the Salt, 700 percent of median on the Verde Mainstem and over 1600 percent of median on the Tonto River.

Snow:
Record or near record snowpack conditions for February 1st existed at several higher elevation locations. Feruary 1st snowpack conditions were near 300 percent of average in the Verde and upper Salt River Basins.

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

Soil Moisture:
Soils have become saturated in middle to lower elevation areas that received rainfall during January. At higher elevations where snowpack has persisted throughout the winter modeled soil moisture states remain slightly drier compared to this time last year.

Climate Forecasts:
El Nino climate conditions suggest increased chances for precipitation in this area. The El Nino influence was accounted for in generation of these forecasts.

Forecast Summary:
Above average precipitation is anticipated over the next 6-8 weeks due to the El Nino climate conditions. Additional rainfall combined with wet soils and the much above average snowpack are expected to yield February through May runoff volumes from 200 to 300 percent of median. Significant rainfall would result in even larger volumes due to the wet soils.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-January precipitation is near average in the upper Gila River Basin.
January precipitation ranged from 220 to 300 percent of average due to heavy rainfall during the 3rd week of the month.

Streamflow:
January runoff volumes were significant, particularly in the San Francisco drainage. Upper Gila runoff volumes were near 300 to 350 percent of median while those in the San Francisco drainage were near 450 percent of median.

Snow:
Upper Gila Basin snowpack conditions increased to 185 percent of average for February 1st. Basin snowpack conditions in San Francisco drainage were near 225 percent of average on February 1st.

Upper Gila Basin Snow Plot.
San Francisco Basin Snow Plot

Soil Moisture:
Wetter soils now exist in the Gila Basin areas that received rainfall during January. At higher elevations where snowpack has persisted through the winter, modeled soil states have changed little from early in the season. Soil moisture states in the San Francisco drainge were wetter entering the season compared to last year.

Climate Forecasts:
El Nino climate conditions suggest increased chances for precipitation in this area. The El Nino influence was accounted for in generation of these forecasts.

Forecast Summary:
Above average precipitation is anticipated over the next 6-8 weeks due to the El Nino climate conditions. Additional rainfall combined with wet soils and the much above average snowpack are expected to yield February through May runoff volumes between 150 and 400 percent of median.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-January precipitation is near 110 percent of average.
Significant precipitation fell in January with monthly totals ranging from 240 to 380 percent of average in the Little Colorado River Basin.

Streamflow:
January streamflow volumes in the Little Colorado Basin varied depending on elevation of the stream gage and proximity to the snowpack. January volumes exceeded 150 percent of median where rainfall had a greater influence on streamflow.

Snow:
Basin snowpack conditions ranged frome 190 to 300 percent of average on February 1st in the southern Headwaters of the Little Colorado Basin.

Little Colorado Southern Headwaters Snow Plot
Central Mogollon Rim Snow Plot

Soil Moisture: Modeled soil moisture remains slightly drier than this time last year under areas of continous snowpack. At lower elevations below the snow line soil moisture states have become much wetter since mid January.

Climate Forecasts:
El Nino climate conditions suggest increased chances for precipitation in this area. The El Nino influence was accounted for in generation of these forecasts.

Forecast Summary:
Above average precpitation is anticipated over the next 6-8 weeks due to the El Nino climate conditions. Additional rainfall combined with the wetter soils and significant snowpack are expected to yield February through May runoff volumes from near 200 to 550 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 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