Significant precipitation occurred in early and late January resulting in very high runoff volumes. January volumes reached near 1500 percent of the monthly median in the Salt River Basin. In the Gila Basin volumes exceeded 400 percent of median with highest volumes on the San Francisco tributary. In the Little Colorado flows were measured in excess of 500 percent of median. Runoff volumes for the February through May period are expected to range from 100 to 300 percent of median. Higher volumes are possible if additional heavy precipitation events occur.

January through May runoff volumes in the Salt River Basin are expected to range from near 150 to 250 percent of the median. The snowpack in the upper Salt Basin ranges from 130 to 200 percent of average and has already exceeded the annual seasonal peak that usually occurs in early March. Due to saturated conditions, additional precipitation during the February through May period may contribute significantly to runoff volumes.

January through May runoff volumes in the Gila River Basin are expected to range from near 100 to 120 percent of median in the Gila headwaters and 150 to 180 percent of median in the San Francsico drainage. The snowpack in the San Francisco Basin ranges from 110 to 200 percent of average and has exceeded the average seasonal peak. Due to saturated conditions, additional precipitation during the February through May period may result in significant contribution to runoff volumes.

January through May runoff volumes in the Little Colorado Basin are expected to range from near 130 to 320 percent of median. Above average precipitation was received in December and January. Snowpack in the Little Colorado southern headwaters is near 200 percent of average and has exceeded the average seasonal peak. Due to saturated conditions, additional precipitation during the Februar through May period may result in significant contribution to runoff volumes.

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