The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was near 77 percent of average in the upper Bear Basin. April precipitation was 139 percent of average.

Streamflow:
The Bear River at stateline recorded 128 percent of average streamflow. The Logan River above State Dam recorded 64 percent of average streamflow.

Snowpack:
May 1st snow water equivalent was 64 percent of average for the Bear Basin as a whole.


Upper Bear River Basin Snow Plot.
Bear River Below Woodruff Narrows Reservoir Snow Plot.
Bear River Basin Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom.

Climate Forecasts:
Climate forecasts were not a factored into the northern Utah forecasts because there is not a strong correlation between El Nino conditions and winter precipitation.

Forecast Summary:
Wet and cool April conditions improved this months water supply forecasts by 16 percent over last months median forecast. April through July seasonal volume forecasts now range between 25 and 79 percent of average with a median forecast volume of 56 percent of average. The residual forecast volumes for May through July range from 27 to 79 percent of average with a median forecast volume of 46 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was 76 percent of average in the Weber Basin. April precipitation was 140 percent of average.

Streamflow:
The Weber at Oakley recorded 67 percent of average streamflow.

Snowpack:
May 1st snow water equivalent was 73 percent of average for the Weber and Ogden River Basins.

Weber River Basin Snow Plot.
Upper Weber River Basin Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom.

Climate Forecasts:
Climate forecasts were not a factored into the northern Utah forecasts because there is not a strong correlation between El Nino conditions and winter precipitation.

Forecast Summary:
Wet and cool April conditions have improved this months water supply forecasts by 26 percent over last months median forecast volume. April through July seasonal volume forecasts now range between 25 and 74 percent of average with a median forecast volume of 65 percent of average. The residual forecast volumes for May through July range from 43 to 74 percent of average with a median forecast volume of 63 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was near 87 percent of average. April precipitation was 154 percent of average.

Streamflow:
Big Cottonwood Creek recorded 70 percent of average streamflow.

Snowpack:
May 1st snow water equivalent was 89 percent of average for Six Creeks Basin.

Six Creeks River Basin Snow Plot.

Big and Little Cottonwood Canyons Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom.

Climate Forecasts:
Climate forecasts were not factored into the northern Utah forecasts because there is not a strong correlation between El Nino conditions and winter precipitation.

Forecast Summary:
Six Creeks water supply conditions improved by 5 percent over last months median forecast volume. April through July seasonal volume forecasts now range between 46 and 85 percent of average with a median forecast of 65 percent of average. The residual forecast volumes for May through July range from 48 to 82 percent of average with a median forecast volume of 69 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October thought April precipitation was 77 percent of average. April precipitation was 136 percent of average.

Streamflow:
April streamflow was 65 percent of average for the Provo at Woodland.

Snowpack:
May 1st snow water equivalent for Utah Lake was near 62 percent of average in the basin as a whole, not including the Jordan River and Six Creeks.

Provo River, Utah Lake Basin Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom.

Climate Forecasts:
Climate forecasts were not factored into the northern Utah forecasts because there is not a strong correlation between El Nino conditions and winter precipitation here.

Forecast Summary:
Wet and cool April conditions improved water supply conditions by 18 percent over last months median forecast volume. April through July seasonal volume forecasts now range between 38 and 70 percent of average with a median forecast volume of 68 percent of average, up 18 percent from last month. The residual forecast volumes for May through July range from 45 to 71 percent of average with a median forecast volume of 65 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 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