The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation remains much above average in the Upper Colorado mainstem basin at 130 percent of average. March precipitation was near 125 percent of average in the basin as a whole. However, the uppermost headwaters of the basin received near 150% of average precipitation for the month.

Snow:
April 1st snow water equivalent was near 130 percent of average in the basin as a whole. This is significant for this time of year as it is also near 130% of the average seasonal peak. Many snotel sites in the upper portion of the basin have snow water equivalent values in the top 5% of their historical records, with a few at record levels.
--- Upper Colorado basin snow water equivalent plot

Streamflow:
March streamflow was near 100 percent of average.

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

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

Forecast Summary:
Almost all forecast volumes were raised from last month due to yet another month of above average precipitation combined with the much above average snow water equivalent at this point in the season. Current April through July streamflow volume forecasts range between 120 and 150 percent of average with a median value of 135 percent. Many of these forecast volumes are in the top five of historical volumes observed since 1970.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 115 percent of average in the Gunnison basin. March precipitation was 90 percent of average.

Snow:
April 1st snow water equivalent was near 115 percent of average in the Gunnison basin; this is around 110% of the seasonal peak.
--- Gunnison basin snow water equivalent plot

Streamflow:
March streamflow was 90 percent of average.

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

Climate Forecasts:
Climate forecasts were not a factor because there is not a strong correlation between La Nina conditions and winter precipitation in the Gunnison basin.

Forecast Summary:
March precipitation throughout the Gunnison basin was average at 90%. Seasonal precipitation for the Gunnison basin dropped a little from last month to 115% of average. April 1st seasonal snow water equivalent for the Gunnison was above average with 115%; whereas the snow water equivalent is 110% of the average seasonal peak. Since there was a slight increases in the seasonal snow water equivalent in the northern portions of the Gunnison basin, the current April through July streamflow volume forecasts remained the same from last month's forecast. Current April through July streamflow volume forecasts range between 83 and 133 percent of average with a median value of 110 percent.

The following conditions influenced this month's forecasts:

Precipitation:
Seasonal October through March precipitation was 95 percent of average in the entire Dolores basin. March precipitation was just 60 percent of average.

Snow:
April 1st snow water equivalent was 85 percent of average in the Dolores basin as a whole; this is about 75% of the seasonal peak.
--- Dolores basin snow water equivalent plot

Streamflow:
March streamflow was 60 percent of average.

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

Climate Forecasts:
The correlation of La Nina and April through July water volumes in the Dolores basin is small that it did not influence the forecast process.

Forecast Summary:
March precipitation throughout the Dolores basin was much below average at 60%. Seasonal precipitation for the Dolores basin dropped from last month to 95% of average. April 1st seasonal snow water equivalent for the Dolores was average with 85%; whereas the snow water equivalent is 75% of the average seasonal peak. Since the percent of average for both seasonal snow water equivalent and seasonal precipitation decreased from last month, the current April through July streamflow volume forecasts dropped in the Dolores Basin from last month's forecast. Current April through July streamflow volume forecasts range between 68 and 71 percent of average, with a median value of 70 percent.

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