New 1981-2010 Averages being used this year.
Note: This publication is currently undergoing major revisions. The current publication will be replaced with a new publication based on stakeholder requirements and scientific advances. We expect to begin sharing details on this soon. If you have input on content, format, or publication frequency at any time, please contact us at Water Supply Outlook, June 1, 2012

Sevier Water Supply Outlook, June 1, 2012

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


Sevier Summary

*Median of forecasts within each basin.

Sevier Basin Conditions

The following conditions influenced this month's forecasts:

Seasonal October through May precipitation was below average, at 80 percent of average.

May precipitation was much below average, at 10 percent of average, in the Sevier River basin.

Streamflow for the Sevier River at Hatch was 50 percent of average for May.

The remaining portions of the snowpack melted out during May in the Sevier River Basin. As of June 1st, the snowpack has melted out in the overall Sevier River Basin, as well as in the headwater areas.

Sevier River Drainage Snow Plot.
Sevier River Basin Headwaters Snow Plot.
Lower Sevier River Basin Below Piute Snow Plot.

Soil Moisture:
Modeled soil moisture content was above average in the Sevier River headwater areas going into the winter.

Climate Forecasts:
Generally, climate scenarios like El Nino and La Nina do not strongly influence conditions in the Sevier River Basin. The southern part of the basin sees more of an influence from El Nino and La Nina than the northern part of the basin does. However, even in the southern part of the basin, the statistical correlations between climate indices like the Southern Oscillation Index and streamflow volumes are minor. As such, climate conditions are given only low weight, if any, in our water supply forecasts for the Sevier River basin.

Forecast Summary:
By June 1st, the snowpack melted out in the Sevier River Basin, even in the headwater areas. May precipitation was much below average, at 10 percent of average. While April streamflows were above average at most locations in the Sevier River Basin due to early snowmelt, streamflows have fallen to much below average for May due to lack of snowpack and precipitation in May. The Sevier River at Hatch monthly streamflow volume for May was 50 percent of average.

Volumes during the June-July period are expected to range from 14 to 53 percent of average. Current April through July Seasonal volume forecasts range between 28 and 70 percent of average. The median April through July forecast volume is 50 percent of average.

The forecasts for the Sevier River at Hatch, the Sevier River near Kingston, the East Fork of the Sevier River, Piute Reservoir, and the Sevier River near Gunnison are 'Regulated or Observed' flow forecasts rather than 'Natural or Unregulated' forecasts, which are corrected for all upstream diversions.

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

Sevier Specific Site Forecasts (kaf)

Click site name for graph.
Hatch *April-July22245027
Kingston, Nr *April-July79.22812
Ef Sevier
Kingston, Nr *April-July21257128
Piute Res, Marysville,nr *April-July27304534
Clear Ck
Sevier, Nr, Diversions, Abv April-July11125713
Salina Ck
Emery, Nr April-July2.83.3424
Manti Ck
Manti, Nr, Dugway Ck, Blo April-July895411
Gunnison, Nr *April-July33424250
Beaver, Nr April-July10.6124613.5
Coal Ck
Cedar City, Nr April-July910.45412

*Regulated Forecast, i.e. Observed flow uncorrected for upstream diversion.
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).

Sevier End of Month Reservoir Contents (kaf)

Last Year
Last Year
untitled Otter Ck
Otter Creek Res, Antimony, Nr 52.5 46.0 88 52.5 100
untitled Sevier
Piute Res, Marysville,nr 71.8 50.6 70 66.1 92
untitled Gunnison Reservoir
20.3 18.0 89 16.9 83
untitled Sevier Bridge Reservoir, Juab, Nr
236.0 191.7 81 205.1 87
untitled Beaver
Minersville Res, Minersville, Nr 23.3 19.2 82 21.0 90
TOTAL 403.9 325.5 81 361.6 90

Monthly Streamflows

Precipitation Maps


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.

Rounding Conventions:
RangeRound to
1000+3 significant digits

Streamflow: The volume of water that flows past a specific stream site.

Water Year: The 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends. Thus, the year ending September 30, 2008, is called the "2008 water year."

Additional Information

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

Hydrologist: S. Bender