The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October-January precipitation was near 255 percent of average in the Virgin Basin headwaters, and 130 to 280 percent of average basin wide.

January precipitation was near 10 percent of average in the Virgin Basin headwaters, and 5 to 35 percent of average throughout the remainder of the basin.

Snow:
February 1st snowpack in the Virgin River Basin ranged from 150 to 215 percent of average at elevations above 7500 feet. Above average temperatures and dry conditions in January allowed most lower elevation snow to melt off.

Virgin River Basin Snow Plot.

Streamflow:
January streamflow volumes were near the 1971-2000 median on the Virgin Basin headwaters.

Soil Moisture:
Above average soil moisture conditions exist throughout the Virgin River Basin.

Climate Forecasts:
La Nina climate conditions suggest slightly decreased chances of precipitation in this area. The La Nina influence was considered in generation of these forecasts.

Forecast Summary:
Significant precipitation in October and December resulted in above average soil moisture conditions and a high elevation snowpack that has exceeded the seasonal peak, which typically occurs in late March or early April. Dry conditions in January, more typical of existing La Nina climate conditions, resulted in decreased April-July runoff forecasts. Above median volumes are still anticipated at this time, however continued dry conditions may result in further decreases to forecast volumes. As of Februay 1st April-July runoff volumes are forecasted to range between 245 to 260 percent of median, or 145 to 160 percent of average.

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