Note: This publication is currently undergoing major revisions. The current publication will be replaced with a new publication based on stakeholder requirements and scientific advances. We expect to begin sharing details on this soon. If you have input on content, format, or publication frequency at any time, please contact us at cbrfc.webmasters@noaa.gov.Lake Powell Water Supply Outlook, February 1, 2009

Lake Powell Water Supply Outlook, February 1, 2009


Prepared by Alcorn
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Lake Powell Sub-Basin Summaries

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.



*Median of forecasts within each basin.


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.



*Median of forecasts within each 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 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.



*Median of forecasts within each basin.




Upper Green Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Yampa/White Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Duchesne Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Lower Green Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Upper Colorado Mainstem Basin Conditions

-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%.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Gunnison Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Dolores Basin Conditions

-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.



* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

San Juan Basin Conditions




* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

















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).

Reservoir Monthly Inflow Forecasts



















Monthly Streamflows

















Precipitation Maps