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 in generating our forecasts. At the time of this publication, seasonal precipitation is near normal for most of the region. Snowpack ranges from above average to below average in the major tributaries of the Green River.

There was a large discrepancy in the January precipitation between the northern half of the Colorado River Basin and the southern half. The Upper Colorado Basin had 120% of average precipitation during the month, while the Gunnison Basin had 80% and the Dolores Basin had just 55% of average. The February 1st snow water equivalent percent of average decreased from January 1st in the Gunnison and Dolores basins but is still above average, as it is in the Upper Colorado.

-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 January was mostly below average for the San Juan.

-Snowpack/Precipitation...Snow water equivalents for the entire San Juan Basin on February 1st was 115 percent of average. Precipitation over the San Juan Basin for January was much below average with 55 percent. Seasonal precipitation for the San Juan Basin decreased to 105 percent of average.

-Short Term Precipitation Forecast...The forecast models through the end of the first week of February keep the San Juan Basin relatively dry.

-General Discussion...The CPC guidance has the possibility of above average precipitation and below normal temperatures for the second week of February. However, for February through April, CPC suggests a chance for below average preciptation. Due to the below average soil moiture in the upper basin this fall and the combination of current snowpack conditions and the CPC forecast, the median April-July forecast for the San Juan Basin is 110 percent of average.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Upper Green Basin. Observed streamflow for the month of January was 90 percent of average.

-Snowpack/Precipitation...In the Upper Green Basin, January precipitation was 105 percent of average. The basinwide to date snowpack condition is 90 percent of average with individual Snotel stations ranging from 43 to 113 percent of average.

-General Discussion...The 30 Day and 90 Day CPC guidance shows equal chances for above, normal, or below precipitation. While the antecedent soil moisture conditions will not change prior to runoff, there is ample time to accumulate snow in the upper basin. April through July forecast indicate below average to average runoff volumes.

-Model Soil Moisture/Observed Streamflow...While soil moisture indicate drier than average Fall conditions in portions of this region, headwater basins had near average conditions. Therefore, soil moisture deficits are not adversely effecting model guidance as much as in other regions. Observed streamflow for the month of January was near average.

-Snowpack/Precipitation...Currently, the Yampa and White River basins has the highest snowpack conditions within the Green, with most Snotel stations having values greater than 115 percent of average values on February 1st. Observed streamflow for the month of January was near average.

-General Discussion...The 30 Day and 90 Day CPC guidance shows equal chances for above, normal, or below precipitation. April through July forecast runoff volumes for the Yampa and White Basins ranged from near average to above average.

-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 January was near average.

-Snowpack/Precipitation...The snowpack condition in the Duchesne Basin on February 1st is the same as January 1st at 85 percent of average. However, some Snotel stations located in the Eastern portion of the Uinta South slope continue to report below average conditions. January precipitation was 95 percent of average.

-General Discussion...The 30 Day and 90 Day CPC guidance shows equal chances for above, normal, or below precipitation. Forecasts range below average on the headwaters of the basin to much below average at downstream locations.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Lower Green Basin. Observed streamflow for the month of January was near average.

-Snowpack/Precipitation...The Lower Green Basin snowpack condition was 85 percent of average on February 1st. January precipitation was 110 percent of average.

-General Discussion...The 30 Day and 90 Day CPC guidance shows equal chances for above, normal, or below precipitation. Forecasts remain at near average to below average.

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

-Snowpack/Precipitation... January precipitation was 120% of average in the Upper Colorado River Basin keeping the water year precipitation at 110% of average. The basin wide February 1st snow water equivalent percent of average also held steady, as compared to January 1st, at 125% although some individual sub-basins did see changes. The Muddy Creek basin, which includes Wolford Mountain Reservoir, had the greatest gain in the snowpack and is now over 110% of average, compared to less than 90% of average at the beginning of January. On the flip side, the Mill Creek basin in Utah near the Colorado border had a decrease of over 30% of average in its snowpack from last month. The Roaring Fork basin snow water equivalent percent of average decreased by about 10% from last month, but is still the highest in the Upper Colorado Basin at over 130% of average.

-General Discussion... Changes to the April through July streamflow volume forecasts from last month generally corresponded to the changes in the snowpack. Muddy Creek had the biggest increase going from 92% to 103% of average and Mill Creek had the biggest decrease going from 106% to 96%. The rest of the forecast volumes remained the same or were increased up to 5% over last month's forecasts reflecting changes in snow water equivalent. The April through July streamflow volume forecasts now range between 96% and 116% of average, with a median value of 110%.

-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 January was average for the Gunnison.

-Snowpack/Precipitation...Precipitation over the Gunnison Basin as a whole for January was below average at 80 percent. However, the northern portions of the basin were near average while the southern portions were much below average. As a result, the February 1st snow water equivalent percent of averages changed very little from the January 1st values in the East River and North Fork Gunnison drainages, and dropped 5-10 percent in the Tomichi and Lake Fork drainages. Seasonal precipitation for the Gunnison is 110 percent of average and overall snow water equivalent remains above average at 115% of average.

-Short Term Precipitation Forecast...The forecast models through the first week of February keep the Gunnison Basin relatively dry with slighly above average temperatures.

-General Discussion...The CPC guidance shows the possibility of above average precipitation and below normal temperatures for the secound week of February. However, for February through April, CPC suggests a chance for above average temperatures and below average preciptation. Due to the average soil moiture in the upper basin this fall and the combination of current snowpack conditions and the CPC forecast, the median April-July forecast for the Gunnison Basin is 110 percent of average. This is up 5 percent from last month's forecast due to the average January precipitation and steady snowpack across the northern portions of the Gunnison.

-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 January was mostly below average for the Dolores.

-Snowpack/Precipitation...As of February 1st, snow water equivalents across the Dolores were currently 120 percent of average. Precipitation over the Dolores Basin for January was much below average with 55 percent. Seasonal average precipitation for the Dolores Basin is average with 100 percent.

-Short Term Precipitation Forecast...The forecast models through the first week of February keep the Dolores Basin relatively dry with above average temperatures.

-General Discussion...The CPC guidance shows the possibility of above average precipitation and below normal temperatures for the secound week of February. However, for February through April, CPC suggests a chance for above average temperatures and below average preciptation for the Dolores Basin. Due to the below average soil moiture in the upper basin this fall and the combination of current snowpack conditions and the CPC forecast, the median April-July forecast for the Dolores Basin is 105 percent 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