The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was 86 percent of average in the upper Bear Basin. April precipitation was 77 percent of average.

Streamflow:
The Bear River at Utah/Wyoming Stateline last month was 172 percent of average. The Bear River at Stewart Dam was 76 percent of average. The Logan River above State Dam was estimated at 115 percent of average streamflow.

Snowpack:
As of May 1st the snowpack is all but gone below 8800ft and is much below average as a whole. The current snow water equivalent for the Bear Basin is 32 percent of average. As of water year 2012 the CBRFC has re-calculated all snow stations to reflect the new 30 year average from 1981-2010.


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. Modeled soil moisture states indicate above average moisture conditions as of April 1st. This is a contributor to the above average baseflows in the Bear River Basin.

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

Forecast Summary:
Overall the winter of 2012 has been drier and warmer than average. Seasonal precipitation throughout the Bear Basin as of May 1 was 86 percent of average. Indexed snow water equivalents are currently 32 percent of average with snow remaining only in the upper elevation zones. Streamflow forecast have been reduced significantly since March 1st due to below average precipitation and warmer than average temperatures causing snow to melt out early. The May through July forecasts are now ranked in the top 5 lowest years on record. April through July seasonal volume forecast range from 34 to 58 percent of average with a median volume of 51 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation is 75 percent of average. April precipitation was 85 percent of average.

Streamflow:
The Weber at Oakley gage was estimated to be 96 percent of average. The inflow to Rockport Reservoir was 73 percent of average.

Snowpack:
As of May 1st the snowpack is all but gone below 8800ft and is much below average as a whole. The current snow water equivalent index is 29 percent of average. As of water year 2012 the CBRFC has re-calculated all snow stations to reflect the new 30 year average from 1981-2010.

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

Soil Moisture:
Modeled Soil Moisture, click on map to zoom. Modeled soil moisture states indicate above average moisture conditions as of December 1st. This is a contributor to the above average baseflows in the Weber River Basin.

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

Forecast Summary:
Overall the winter of 2012 has been drier and warmer than average. Seasonal precipitation throughout the Weber River Basin as of May 1 was 75 percent of average. Indexed snow water equivalents on May 1st were 29 percent of average with snow remaining only in the upper elevation zones. Streamflow forecast have been reduced significantly since March 1st due to below average precipitation and warmer than average temperatures causing snow to melt early. The May through July Weber Basin forecasts are now ranked in the top 10 lowest years on record. April through July seasonal volume forecasts range between 36 and 56 percent of average with a median forecast volume of 42 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was near 78 percent of average. April precipitation was 97 percent of average.

Streamflow:
April streamflow for City Creek near Salt Lake City was 60 percent of average. Big Cottonwood Creek nr Salt Lake City was 84 percent of average.

Snowpack:
As of May 1st the snowpack is all but gone below 8800ft and is much below average as a whole. The current indexed snow water equivalent is 32 percent of average. As of water year 2012 the CBRFC has re-calculated all snow stations to reflect the new 30 year average from 1981-2010.

Six Creeks Headwaters Basins Snow Plot.

Big and Little Cottonwood Canyons Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom. Modeled soil moisture states indicate mostly above average mositure conditions as of December 1st. Although flows are dropping in the Six Creeks basin, above average soil moistures have been influencing baseflows through the fall and April was the first month that they dropped to near average.

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

Forecast Summary:
Overall the winter of 2012 has been drier and warmer than average. Seasonal precipitation throughout the Weber River Basin as of May 1 was 78 percent of average. Indexed snow water equivalents on May 1st were 32 percent of average with snow remaining only in the upper elevation zones. Streamflow forecast have been reduced significantly since March 1st due to below average precipitation and warmer than average temperatures causing snow to melt early. Many of the May through July Six Creeks forecasts are now ranked near or in the top 10 lowest years on record. April through July seasonal volume forecasts range between 22 to 58 percent of average with a median forecast of 41 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October thought April seasonal precipitation was 76 percent of average. April precipitation was 72 percent of average.

Streamflow:
Streamflows for the Provo at Woodland was 118 percent of average. Unregulated inflow to Utah Lake was 72 percent of average which represents a significant drop from the previous month.

Snowpack:
As of May 1st the snowpack is all but gone below 8800ft and is much below average as a whole. Current snow water equivalent measurements are 24 percent of average. As of water year 2012 the CBRFC has re-calculated all snow stations to reflect the new 30 year average from 1981-2010.

Provo River, Utah Lake Drainage Snow Plot.

Soil Moisture:
Modeled Soil Moisture, click on map to zoom. Modeled soil moisture states indicate mostly average to above average conditions as of December 1st. This is a contributor to the current baseflows conditions in the Provo and Utah Lake forecast.

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

Forecast Summary:
Overall the winter of 2012 has been drier and warmer than average. Seasonal precipitation throughout the Utah Lake and Provo River Basins as of May 1 was 78 percent of average. Indexed snow water equivalents on May 1st for the Provo/Utah Lake basin were 24 percent of average with snow remaining only in the upper elevation zones. Streamflow forecast have been reduced significantly since March 1st due to below average precipitation and warmer than average temperatures causing an early melt which diminshes watersupply. Many of the May through July forecasts are now ranked between the 19th-7th lowest years on record. April through July seasonal volume forecasts range between 30 and 60 percent of average with a median forecast volume of 41 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