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Sevier Water Supply Outlook, February 1, 2009

Prepared by Brent Bernard
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah


Sevier Summary

Snow Water Equivalent & Precipitation - conditions across the Sevier River drainage were affected this last month by above average temperatures which decreased snow water equivalents by 10%. Snow water equivalents decrease slightly to 100% of average due to rain on snow at lower elevations and several periods of above average temperature. Monthly precipition however totalled 105% of average which kept overall conditions at average. Season precipitation ended the month at 110% of average.

Soil Moisture & Streamflow - Currently we have no models soil moisture grids for the Sevier River Basin. Streamflow conditions were higher this month due to rain and melting snow. This can be attributed to the temperature anomolies for both max and min temperatures in January. Streamflows on the Sevier at Kingston were 90% of average.

Short Term Precipitation Forecasts - Weather guidance from National Weather Service models are indicating a period of wet weather during the next 5-10 days in the Sevier River Basin. Short term CPC guidance shows the possibility of above average precipitation for the second week of February.

General Discussions - Longer range predictions from NOAA's Climate Prediction Center are now factoring in a weak La Nina episode, predicted to last through the spring of 2009. Please reference the web link above for further details and effects within the Sevier River Basin. Volumetric forecasts were slightly lower this month due to declining snow water equivalents as a percent of average. Overall the volumetric forecasts ranged from 85% of average at the Sevier near Gunnison below San Pitch to 103% of average for the Sevier at Kingston. Both of these forecast points represent regulated/observed forecasts rather than corrected natural flow forecasts.

*Median of forecasts within each basin.

Sevier Basin Conditions

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

Sevier Specific Site Forecasts (kaf)

Click site name for graph.
Hatch April-July30549878
Kingston, Nr April-July9329773
Ef Sevier
Kingston, Nr April-July173610355
Marysvale, Nr, Piute Dam, Blo April-July418796133
Gunnison, Nr, San Pitch, Blo April-July149085275
Chicken Ck
Levan, Nr April-July1.33.6807.7
Oak Ck
Oak City, Nr, Little Ck, Abv April-July0.71.4842.3
Beaver, Nr April-July15.13011145
Minersville Res, Minersville, Nr April-July4.31710244
Coal Ck
Cedar City, Nr April-July11.52211432

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 Reservoir Contents (kaf)

Last Year
Last Year
untitled Otter Ck
Otter Creek Res, Antimony, Nr 52.5 24.7 47 29.3 56
untitled Sevier
Piute Res, Marysvale, Nr 71.8 29.2 41 38.6 54
untitled Gunnison Reservoir
20.3 8.9 44 1.1 5
untitled Sevier Bridge Reservoir, Juab, Nr
236.0 103.7 44 141.0 60
untitled Beaver
Minersville Res, Minersville, Nr 23.3 8.9 38 7.3 31
TOTAL 403.9 175.4 43 217.3 54

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 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.

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: Brent Bernard