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.Upper Colorado Water Supply Outlook, May 1, 2010

Upper Colorado Water Supply Outlook, May 1, 2010


Prepared by Brenda Alcorn, Tracy Cox
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Upper Colorado Summary




*Median of forecasts within each basin.


Upper Colorado Mainstem Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was near 90 percent of average in the Upper Colorado mainstem basin. April precipitation was near 140 percent of average.

Snow:
May 1st snow water equivalent was near 75 percent of average in the basin as a whole.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
April streamflow was near 110 percent of average.

Soil Moisture:
Modeled soil moisture states were near average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between El Nino conditions and winter precipitation in the Upper Colorado mainstem basin.

Forecast Summary:
Precipitation and streamflows were much above average and above average for the month of April in the Upper Colorado Basin. However, May 1st snow water equivalent remained below average at 75%. May through July streamflow volume forecasts range from 58 to 85 percent of average, with a median value of 72%. April precipitation and streamflow conditions resulted in a 5-15% increase to the April through July volume forecasts for most locations. The Upper Colorado basin April through July volume forecasts now range between 60 and 87 percent of average, with a median value of 75%.



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

Gunnison Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was 95 percent of average in the Gunnison Basin. April precipitation was 115 percent of average.

Snow:
May 1st snow water equivalent was 80 percent of average in the Gunnison Basin.
--- Gunnison basin snow water equivalent plot

Streamflow:
April streamflow was 125 percent of average.

Soil Moisture:
Modeled soil moisture states were below average heading into the winter.

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between El Nino conditions and winter precipitation in the Gunnison Basin.

Forecast Summary:
April precipitation was above average in the Gunnison Basin as a whole, as were the monthly streamflow volumes. However, May 1st snow water equivalent for the Gunnison dropped to below average at 80%. May through July volume forecasts range from 65 to 84 percent of average, with a median value of 75%. This resulted in very little change overall to the April through July volume forecasts, with some points going up a little and others down a little. The Gunnison Basin April through July forecasts now range between 73 and 91 percent of average, with a median value of 80%.



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

Dolores Basin Conditions

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through April precipitation was 105 percent of average in the entire Dolores Basin. April precipitation was 105 percent of average.

Snow:
May 1st snow water equivalent was 70 percent of average in the Dolores Basin.
--- Dolores basin snow water equivalent plot

Streamflow:
April streamflow was 120 percent of average.

Soil Moisture:
Modeled soil moisture states were below to much below average heading into the winter.

Climate Forecasts:
The correlation of El Nino and May through July water volumes in the Dolores Basin is so small that it did not influence the forecast process.

Forecast Summary:
Although April precipitation was near average in the Dolores Basin as a whole, the Dolores River headwaters were once again below average at 85%. In addition, the May 1st snow water equivalent was below average at 70%. May through July volume forecasts range from 62 to 75 percent of average, with a median value of 67%. Even with the above average April streamflow volumes, this resulted in about a 5% decrease in the April through July forecast volumes. The Dolores Basin April through July forecasts now range between 75 and 80 percent of average, with a median value of 75%.



* 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).

Reservoir Monthly Inflow Forecasts







Monthly Streamflows









Precipitation Maps








Hydrologist: Brenda Alcorn, Tracy Cox