The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through May precipitation was near 86 percent of average in the upper Bear Basin. May precipitation was 145 percent of average.

Streamflow:
The Bear River inflow to Woodruff Narrows Reservoir was recorded 51 percent of average streamflow. The Logan River above State Dam recorded 45 percent of average streamflow.

Snowpack:
This year's snow peaked at approximately 70 percent of the average maximum. A brief period of warm temperatures from mid April until April 26th created a good melt before a late season winter storm dropped more snow and again delayed the melt until mid May. As of June 3 the only significant snow remaining is on north slopes above 9100 feet.


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:
Another Wet and cool month held water supply forecasts steady with no change in the April through July median. April through July seasonal volume forecasts range between 25 and 79 percent of average with a median forecast volume of 56 percent of average. The residual forecast volumes for June through July range from 37 to 93 percent of average with a median forecast volume of 61 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through May precipitation was 84 percent of average in the Weber Basin. May precipitation was 132 percent of average.

Streamflow:
The Weber at Oakley recorded 47 percent of average streamflow due to cool weather and little snowmelt making it to the channel.

Snowpack:
This year's snow pack peak accumulation occurred during mid April at approximately 80 percent of average. The melt was delayed by a series of late spring storms that by mid April caused the snow plots to merge with average on the declining limb of the snow plots. Currently the only significant snow left in the Weber Basin is above 9500 feet and should melt rapidly during the next 10 days or less.

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 conditions persisted thoughout the Weber basin in May, however there was no change this month to the median April though July forecast volume. April through July seasonal volume forecasts range between 24 and 97 percent of average with a median forecast volume of 65 percent of average. The residual forecast volumes for June through July range from 50 to 100 percent of average with a median forecast volume of 65 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through May precipitation was near 97 percent of average. May precipitation was 155 percent of average.

Streamflow:
Big Cottonwood Creek recorded 44 percent of average streamflow due to unseasonably cool temperatures.

Snowpack:
This year's seasonal peak snow occurred during mid April at approximately 90 percent of average before the first melt began. Then at the end of April a large late season winter storm dropped 7 feet of snow in 4 days in the upper Cottonwood Canyons and delayed the melt until Late May. Currently the only significant snow remaining is above 9000 feet is in the American Fork and the Cottonwood Canyons drainages.

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:
Another cool and wet month in April delayed the snow melt runoff however the April through July median forecast volumes remains unchanged from last month. April through July seasonal volume forecasts range between 44 and 84 percent of average with a median forecast of 65 percent of average. The residual forecast volumes for June through July range from 56 to 102 percent of average with a median forecast volume of 82 percent of average.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October thought May seasonal precipitation was 83 percent of average. May precipitation was 114 percent of average.

Streamflow:
Streamflow conditions for the Provo at Woodland was recorded at 49 percent of average. Inflow to Utah Lake was recorded at 63 percent of average.

Snowpack:
This year's seasonal peak snow occurred approximately May 10th at 80 percent of average for the Utah Lake drainage as a whole. Cool weather during late April delayed the melt some what, however as of June 3rd the only significant snow remaining is above 9100 feet in the headwaters of the Provo and American Fork drainages.

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:
Despite the cool and wet weather during May there was little change in the median April through July forecast median volume. April through July seasonal volume forecasts range between 53 and 72 percent of average with a median forecast volume of 67 percent of average. The residual forecast volumes for June through July range from 50 to 87 percent of average with a median forecast volume of 77 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