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Virgin Water Supply Outlook, January 1, 2010

Prepared by G. Smith
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah


Virgin Summary

Forecast Note
Forecasts in this publication are now being referenced to the 1971-2000 median value. Median represents the mid point of all the April-July volumes observed during this 30 year period. Half of the observed volumes are above this value, and half below this value. Historically forecasts were represented as a percent of the 1971-2000 average (or mean) value. However, the average values were skewed by a few very wet years and are not considered the best metric on which to reference forecasts.

*Median of forecasts within each basin.

Virgin Basin Conditions

The following conditions influenced this month's forecasts:

Seasonal October-December precipitation was near 90 percent of average in the Virgin Headwaters, and 65 percent of average basin wide.

December precipitation was near 190 percent of average in the Virgin Headwaters, and 120 to 170 percent of average throughout the remainder of the basin.

January 1st snowpack in the Virgin River Basin ranged from 105 to 290 percent of average. January 1st snowpack is near 50 percent of the average seasonal peak.

Virgin River Basin Snow Plot.

Soil Moisture:
Below average precipitation during the autumn months created drier soil moisture conditions.

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

Forecast Summary:
Drier soil moisture conditions tend to reduce forecast volumes. However, the presence of El Nino climate conditions combined with much above average snowpack resulted in April-July forecast volumes between 115 and 135 percent of median.

* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

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).

Precipitation Maps

Hydrologist: G. Smith