November modeled soil moisture indicated much below and below average conditions for most of Green River Basin. (Click for November 1st image) This signal is incorporated in the ESP model guidance utilized by the CBRFC to generate forecasts. At the time of this publication, seasonal precipitation is near normal for most of the region. However, April precipitation was much above average in the Upper Green, Duchense, and Lower Green river basins. Snowpack is past the seasonal peaks. Median April water supply forecasts increased in the Upper Green, Duchense, and Lower Green river basins and dropped slighty in the Yampa/White river basin.

April precipitation was above average in the Upper Colorado and Gunnison Basins and near average in the Dolores basin. Snow water equivalent values peaked in the Upper Colorado and Gunnison Basins in the latter part of April with the Upper Colorado reaching 115% of the seasonal average peak and the Gunnison 110%. The Dolores Basin snow water equivalent peaked at the beginning of April at just under 100% of the seasonal average peak. May 1st snow water equivalent values were down quite a bit from their peaks with the Upper Colorado still near average at 95% of average, but the Gunnison and Dolores basins were both below average for this time of year at 80% and 50% of average respectively. Overall, the May 1st April through July forecast runoff volumes are similar to the April 1st forecasts in the Upper Colorado and Gunnison Basins and dropped slightly in the Dolores Basin.

-Model Soil Moisture/Observed Streamflow...Soil moisture for most of the upper basins in the San Juan were below average last fall. This was most likely due to limited monsoonal precipitation over the summer months. Observed streamflow for the month of April was near average in the upper portions of the basin, but below normal in the lower San Juan.

-Snowpack/Precipitation...Snow water equivalent for the entire San Juan Basin on May 1st was 75 percent of average. After three months of much below normal precipitation, the San Juan Basin recieved 95 percent of average precipitation during April. Due to the extremely wet December, seasonal precipitation has stayed near average and is currently 95 percent of average.

-Short Term Precipitation Forecast... As of May 6th, meteorological models were predicting increased chances for above normal temperatures and below normal precipitation through the middle of May.

-General Discussion...Due to the below average soil moisture in the upper basin this fall and the combination of current snowpack conditions and April observed flow, the median April-July forecast for the San Juan Basin is 85 percent of average. All forecasts are exactly the same as those issued April 1st. The median of the May-July forecasts is also 85 percent of average.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Upper Green River basin. Observed streamflow for the month of April was 80 percent of average.

-Snowpack/Precipitation...In the Upper Green River basin, April precipitation was 155 percent of average. On May 1st, the basinwide snowpack was 95 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. April through July guidance indicate below average to near average runoff volumes for points above Flaming Gorge.

-Model Soil Moisture/Observed Streamflow...Fall soil moisture estimates were near average in the headwaters of the Yampa and White River basin. Soil moisture deficits are not adversely effecting model guidance as much as in other regions. Observed streamflow for the month of April was 125 precent of average.

-Snowpack/Precipitation...On May 1st, the basinwide snowpack was 95 percent of average. April precipitation was 115 precent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below average precipitation. April through July guidance indicate runoff volumes from average to much above average for the Yampa and White River basin.

-Model Soil Moisture/Observed Streamflow...Fall soil conditions in the Duchesne were similar to the Upper Green with many basins indicating much below average conditions. Observed streamflow for the month of April was average.

-Snowpack/Precipitation...The snowpack in the Duchesne River basin on May 1st was 75 percent of average. April precipitation was 170 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. Forecasts range from average in the headwaters of the basin to below average at downstream locations.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Lower Green River basin and continues to drive lower model guidance. Observed streamflows for the months of February, March, and April were below average.

-Snowpack/Precipitation...The Lower Green River basin snowpack was 55 percent of average on May 1st. April precipitation was 155 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. Forecasts range from below average to near average with the exception of Ferron Creek forecasted at much below average.

-Model Soil Moisture/Observed Streamflow... Soil moisture was near to above average in the Upper Colorado heading into the winter. April streamflow was 125% of average. This was due, in large part, to elevated flows during the last 10 days of the month when there was decreased storminess and above average temperatures.

-Snowpack/Precipitation... After two months of below average precipitation, the Upper Colorado River Basin received 115% of average precipitation during April. Snow water equivalent was 95% of average on May 1st, however it peaked around 115% of the seasonal average peak on April 20th.

-Short Term Precipitation Forecast... As of May 6th, meteorological models were predicting increased chances for above normal temperatures and below normal precipitation through the middle of May.

-General Discussion... Most of the April through July volume forecasts stayed the same or increased slightly from the April 1st issuance. The most notable exceptions were decreases that occurred at Plateau Creek, which went from 91% to 80%, and Mill Creek, which went from 70% to 56%. The April through July streamflow volume forecasts now range between 56% and 111% of average, with a median value of 105%. The May through July streamflow volume forecasts now range between 53% and 109% 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 April was above average for the Gunnison.

-Snowpack/Precipitation... Precipitation over the Gunnison Basin for April ranged from average in the lower basin to much above average for the headwater basins. The May 1st snow water equivalent percent of average was 80 percent. Seasonal precipitation for the Gunnison is 100 percent of average.

-Short Term Precipitation Forecast... As of May 6th, meteorological models were predicting increased chances for above normal temperatures and below normal precipitation through the middle of May.

-General Discussion... April-July forecasts remained unchanged for the Gunninson Basin except for the North Fork of the Gunnison, which has a slight decrease. The median April-July forecast for the Gunnison Basin remains at 95 percent of average.

-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 April was below average for the Dolores.

-Snowpack/Precipitation... As of May 1st, snow water equivalent across the Dolores was 50 percent of average. The Dolores Basin recieved average precipitation for April. Seasonal precipitation for the Dolores Basin is at 90 percent of average.

-Short Term Precipitation Forecast... As of May 6th, meteorological models were predicting increased chances for above normal temperatures and below normal precipitation through the middle of May.

-General Discussion... With much of the snow pack below 10,000 feet melted and stream flow being below average in the Dolores Basin, April-July volume forecasts have been lowered slightly. The median April-July forecast is now at 80 percent of average, a 5 percent decrease from April 1st.

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