Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
April precipitation was 197 percent of average.
Seasonal, October through April precipitation was 152 percent of average.

Streamflow:
April streamflow for the Logan River nr Logan was 115 percent of average. Woodruff Narrows inflow on the Bear River was 183 percent of average.

Snowpack:
May 1st snow water equivalent was 205 percent of the daily average. Many SNOTEL sites in the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.

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

Soil Moisture:
Modeled Soil Moisture states were near average to above average for the northern Uinta Mountains heading into the winter.

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

Forecast Summary:
Cooler than average temperatures during the month and much above average precipitation on top of already above average snow accumultations have combined to create near record snow pack conditions as of May 1st. Current April through July seasonal volume forecasts remain much above average and range between 156 and 245 percent of average with a median value of 221 percent. Many of these forecast volumes are in the top five historical observed volumes.

Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
April precipitation was 209 percent of average. Seasonal October through April precipitation was 157 percent of average.

Streamflow:
Streamflow above Rockport Reservoir last month were 133 percent of average.

Snowpack:
May 1st snow water equivalent was 197 percent of the daily average. Many SNOTEL sites in the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.

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

Soil Moisture:
Modeled Soil Moisture states were mostly above normal in the western Uinta Mountains near the headwaters of the Weber heading into winter.

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:
Cooler than average temperatures during the month and much above average precipitation on top of already above average snow accumultations have combined to create near record snow pack conditions as of May 1st. Current April through July seasonal volume forecasts remain much above average, and range between 174 and 268 percent of average with a median value of 197 percent. Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
April precipitation was 197 percent of average. Seasonal October through April precipitation was 159 percent of average.

Streamflow:
Streamflows for Emigration Creek near Salt Lake City last month were 166 percent of average.

Snowpack:
May 1st snow water equivalent was 201 percent of the daily average. Many SNOTEL sites in the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.

---Six Creeks River Basin Snow Plot.
---Big and Little Cottonwood Canyons Snow Plot.

Soil Moisture:
Modeled Soil Moisture states were near average in the Six Creeks Basin heading into winter.

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:
Cooler than average temperatures during the month and much above average precipitation on top of already above average snow accumultations have combined to create near record snow pack conditions as of May 1st. Current April through July seasonal volume forecasts are much above average, and range between 150 and 231 percent of average with a median value of 177 percent of average. Many of these forecast volumes are in the top five historical observed volumes.

Many of these forecast volumes are in the top five historical observed volumes.

The following conditions influenced this month's forecasts:

Precipitation:
April precipitation was 196 percent of average. Seasonal October through April precipitation is 159 percent of average.

Streamflow:
Streamflow for the Provo at Woodland last month was 93 percent of average. Unregulated inflows to Utah Lake were 131 percent of average.

Snowpack:
May 1st snow water equivalent was 212 percent of the daily average. Many SNOTEL sites in the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.

---Provo River, Utah Lake Basin Snow Plot.

Soil Moisture:
Modeled Soil Moisture states were average to above average heading into the winter.

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:
Cooler than average temperatures during the month and much above average precipitation on top of already above average snow accumultations have combined to create near record snow pack conditions as of May 1st. April through July seasonal volume forecasts remain much above average and range between 174 and 213 percent of average with a median value of 205 percent. Many of these forecast volumes are in the top five historical observed volumes.

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