Note: This publication is currently undergoing major revisions. The current publication will be replaced with a new publication based on stakeholder requirements and scientific advances. We expect to begin sharing details on this soon. If you have input on content, format, or publication frequency at any time, please contact us at cbrfc.webmasters@noaa.gov.Great Basin Water Supply Outlook, May 1, 2011

Great Basin Water Supply Outlook, May 1, 2011


Prepared by B.Bernard
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Great Basin Summary






*Median of forecasts within each basin.


Bear Basin Conditions

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.



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

Weber Basin Conditions

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.



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

Six Creeks Basin Conditions

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.



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

Utah Lake Basin Conditions

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.



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









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).


Monthly Streamflows









Precipitation Maps








Hydrologist: B.Bernard