March precipitation was below average in the Upper Colorado Basin and much below average in the Gunnison and Dolores basins. The April 1st snow water equivalent was above average in the Upper Colorado Basin and near average in the Gunnison and Dolores basins; this is a decrease in the snow water equivalent percent of average in all basins from March 1st with the largest drop having occurred in the Dolores basin. The decreases in the forecasts from last month for each basin generally follow the decreases in the snow water equivalent percent of average.

-Model Soil Moisture/Observed Streamflow... Soil moisture was near to above average in the Upper Colorado heading into the winter. March streamflow was near average.

-Snowpack/Precipitation... March precipitation was 80% of average in the Upper Colorado River Basin, making it two months in a row with below average precipitation. However, the seasonal precipitation is still near average and the snow water equivalent was still just above average at 110% as of April 1st.

-Short Term Precipitation Forecast... The forecast models through the middle of April suggest that the Upper Colorado Basin will see above average precipitation.

-General Discussion... In general, forecasts were dropped about 5% from last month due to the below average precipitation and the decrease in the snow water equivalent percent of average. Larger drops occurred in the lower part of the basin where the forecasts for Plateau Creek, Colorado near Cisco and Lake Powell had decreases closer to 10% of average. The Mill Creek forecast had the biggest decline going from 96% of average to 70% of average due to the loss of snow in that area. The April through July streamflow volume forecasts now range between 70% and 114% of average, with a median value of 105%.

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the Gunnison was near to slightly below average in the fall. Observed streamflow for the month of March was near average for the Gunnison.

-Snowpack/Precipitation...Precipitation over the Gunnison Basin for March was below average at 70 percent. The April 1st snow water equivalent percent of average was 100 percent, which dropped about 5 percent from March 1st. Seasonal precipitation for the Gunnison is 100 percent of average.

-Short Term Precipitation Forecast...The forecast models through the middle of April suggest that the Gunnison Basin will see above average precipitation.

-General Discussion...Due to the average soil moiture in the upper basin this fall, the current snowpack conditions, and the below average precipitation in March, the median April-July forecast for the Gunnison Basin is 95 percent of average. This is down 10 percent from last month's forecast.

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the Dolores was below average in the fall. This was most likely due to limited monsoonal precipitation during the summer months. Observed streamflow for the month of March was average to below average for the Dolores.

-Snowpack/Precipitation...As of April 1st, snow water equivalent across the Dolores was 95 percent of average, which was about a 15 percent drop from March 1st. Precipitation over the Dolores Basin for March was much below average with 50 percent. Seasonal precipitation for the Dolores Basin dropped to 85 percent of average.

-Short Term Precipitation Forecast...The forecast models through the middle of April suggest above average precipitation.

-General Discussion...Due to the combination of below average soil moiture in the upper basin this fall, current snowpack conditions, above normal temperatures in early March, and the much below average precipitation in March, the median April-July forecast for the Dolores Basin is 85 percent of average. This is down 20 percent from last month's forecast.

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