March brought a mix of conditions to the Green River. The Upper portion of the basin had near average precipitation while the Yampa. Duchesne and Lower Green saw below average to well below average precipitation. Fortunately, temperatures were cool with daily maximums 3-7 Fahrenheit degrees below average and minimums 1 to 3 Fahrenheit degrees below average. This preserved much of the snowpack in the Yampa, Duchense and Lower Green basins where conditions are still above the April 1st average. In the Upper Basin, snowpack improved slightly from 90 percent on March first to 95 percent on April 1st.

March was a much drier month than we have seen so far this winter in the Upper Colorado Basin, especially in the Dolores River Basin which received just 35% of average precipitation during March. The headwaters of the Gunnison and Upper Colorado mainstem basins received close to normal precipitation for the month, while the rest of the areas in those basins received between 40% and 80% of average precipitation. As a result, median forecasts for the April through July runoff volumes dropped 15% in the Dolores Basin and remained steady in the Gunnison and Upper Colorado mainstem basins.

-Model Soil Moisture/Observed Streamflow...Soil moisture for all of the upper basins in the San Juan are near normal. However, soil moisture conditions were above average for the lower portions of the San Juan. Observed streamflow for the month of March was above average for the headwaters of the San Juan, while the lower portions of the San Juan were much above average.

-Snowpack/Precipitation...Snowpack above Navajo Reservoir dropped to 130 percent of average while the Animas and the entire San Juan Basin dropped to 125 percent. Precipitation over the San Juan Basin for March was much below average with 35 percent. Seasonal average precipitation for the San Juan Basin dropped to 120 percent.

-Short Term Precipitation Forecast...The forecast models through five days keep the San Juan Basin relatively dry with near average temperatures into the beginning of next week.

-General Discussion...The current snowpack along with both statistical forecast and ESP numbers suggest lowering the forecast across all of the headwaters of the San Juan. The CPC guidance continues to show the possibility of increased chances of below normal precipitation for April through June across the San Juan Basin.

Near average March precipitation brought the median basin forecast up to 85 percent in the Upper Green. However, dry soil conditions continue to influence the April through July Forecast in the Upper Green. While snowpack in near normal at many sites, modeled soil moisture is well below average with some regions in the 20 to 30 percent of the 30 year average. This accounts for the difference in the snow observations and the April through July runoff forecast.

March precipitation was only 70 percent average. Basin wide, snowpack remained 110 percent on April 1st. Key stations in portions of the Sierra Madre and Park Range increased snowpack. As a result, model guidance increased for some points and the median basin forecast is 125 percent. This increase is seen on the Elk River and Elkhead Creek, which are expected to see April through July volumes that are much above average.

Below average precipitation in March led to a reduction in forecasted volumes for points in the Duchesne River Basin. Continued cool temperatures and the potential for additional storms to impact the area during the first portion of April should keep runoff volumes near average to slightly above average.

The Lower Green Basin had the least March precipitation in the region. Snowpack dropped 15% from the March 1st but is still 120% of the April 1st average. Runoff volumes are anticipated to be near average.

The Upper Colorado mainstem basin as a whole received about 85% of the average March precipitation, but this was not distributed uniformly across the basin. The headwaters on the southern side of the basin above Glenwood Springs received near normal precipitation for the month while areas below this received closer to 50% of average precipitation. Temperatures were a bit on the cool side for the month overall, as they have been for most of the winter. As a result of these near normal precipitation and temperature conditions in the higher elevations during March, the snow water equivalent remained above normal for this time of year at 125% of average on April 1st; this is only a 5% drop from the March 1st percent of average. The Roaring Fork basin snow water equivalent remains the highest in the basin at close to 150% of average. Model soil moisture is still near to just below average at this time as the runoff gets ready to start. Current meteorological models are indicating a chance for continued unsettled weather during the first half of April over western Colorado. If this occurs, there is potential for additional snowpack accumulation, or at the very least little loss of snowpack due to melt. With all this in mind, there were minimal changes made to the forecasts from last month with just a few points in the Eagle and Roaring Fork basins, as well as affected downstream points, being raised slightly. The April through July streamflow forecasts now range between 100% and 150% of average.

Precipitation in the Gunnison Basin varied for the month of March. In the northeast portions of the basin, precipitation was around average. For the rest of the basin, precipitation was below average. April 1st percent of average snow water equivalent in the Gunnison Basin ranges from 105% to 160%. On average, this is a 10% reduction from the March 1st percent of average snow water equivalent. However, overall the snowpack is 130% above the average seasonal maximum accumulation.
Streamflow in the Gunnison Basin was 90% of normal for March. Modeled soil moisture states are around average, except for the North Fork of the Gunnison which is below average. April through July volume forecasts in the Gunnison Basin remained steady except for East River and Gunnison River at Gunnison, where there was a slight increase, and Paonia Reservoir, where there was a slight decrease. Volume forecasts range from 135% to 160% of average.

The Dolores Basin saw monthly precipitation well below average for March. April 1st percent of average snow water equivalent in the Dolores ranges from 110% to 140%. This is a 30% reduction from March 1st percent of average snow water equivalent. However, the cool temperatures in March allowed the snowpack to remain higher than the average seasonal maximum accumulation at 120%.
Streamflow in the Dolores Basin was 125% of average for March. Modeled soil moisture conditions in the basin remain around average. With the well below average precipitation for March, the April through July volume forecasts in the Dolores Basin have been reduced. The forecast for McPhee Reservoir is now 450 kaf. However, this is still above the average of 320 kaf. Volume forecasts in the Dolores Basin range from 135% to 150% 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