Snowpack and Water Supply Briefing January 2013

Uploaded by NWSPendleton on 10.01.2013

Hi, this is Marilyn Lohmann, Service Hydrologist at WFO Pendleton. I will review the mountain
snowpack and water supply forecast across the Pendleton Forecast Area as of January
This map, produced by the Natural Resource Conservation Service shows the percent of
normal snow water equivalent ( or amount of water being held in the snowpack) for the
various basins across the state of Washington. We saw good amounts of snow in the higher
elevations during the month of December. The Lower Snake Basin, has the lowest amounts
across the state with snow water equivalent near 85 percent of normal. In the Cascades,
the snow water was around 120 percent of normal in the Upper Yakima Basin and around 140 percent
of normal in the Lower Yakima Basin. In the next few slides, we will look at a few locations
within the basins to see how the snowpack changed.
  These charts show the snow water equivalent
for the water year, October through September. The blue line is the maximum observed, while
the red line is the minimum. The green line is the average. Using these charts we can
see how the snow water equivalent accumulates through the winter and spring and compare
it to the average. The Touchet Snotel Site is in the Walla Walla Basin , around 5500
feet. We can see the black line showing the observed snow water equivalent has been increasing
through the late fall and winter and is slightly below normal.
The Sasse Ridge Snotel site is located in the Upper Yakima Basin at 4200 feet. Looking
at the black line, we can see there was steady accumulation through the month and is above
The Bumping Ridge Snotel, elevation 4600 feet is in the Central Washington Cascades and
is about the mid point in elevation across the Lower Yakima Basin. This area continued
to see a strong increase during the last part of the month and continues to rise through
early part of January with amounts above normal.  
Across the Oregon portion of the Pendleton Forecast Area, The snow pack is slightly below
normal with the least amount in the far northeast corner with 70 percent of normal for the Grande
Ronde Powder, Burnt and Imnaha Basins. The Upper Deschutes and Crooked Basins are slightly
above normal with 108 percent of normal, while the John Day and Umatilla Basins are 90 percent
of normal. We will take a look a some individual sites within the basins in the next several
In the Lower Deschutes/Columbia Basin, Clear Lake Snotel is at an elevation of 3500 feet.
Looking at the black line, the current year observation, this site saw a strong increase
during mid to late December and is slightly below normal.
In the Upper Deschutes Basin, Three Creek Meadows Snotel site is at about 5600 feet.
We can look at the solid black line and note that the site saw steady accumulation during
December and is near normal. For the John Day Basin, we can look at the
Blue Mountain Springs Site at 5900 feet. This location show a steady increase through the
month of December, but remains below normal.  
For the Blue Mountains, we can look at the High Ridge Site at 4900 feet. Looking at the
black line, we can see that there was steady accumulation during the month of December,
but still remains below normal.  
In the Grande Ronde Basin, the Moss Springs Snotel Site at 5800 feet also showed some
increase during the month, but remain much below normal.
  The Northwest River Forecast Center uses Ensemble
Streamflow Prediction or ESP generated forecasts as the official water supply method. This
year, new 30 year runoff normals covering the years 1981 to 2010 are being used. For
all of the published locations, the updated normals are less than the 1971-2000 dataset.
This is due to the relatively dry runoff period from 2001-2010. New ESP forecast will be published
on the NWRFC website at a minimum of once per week, but may be updated daily as the
discrestion of the NWRFC. For updated forecasts and a more information of ESP forecasts, please
see the river forecast center’s website at the address given.
For the Yakima River System, we will look at the Yakima River near Parker. Looking at
the plot, the solid green line is the 30 year normal. The box plots show the entire range
of forecast values with the blue dot the 50% percentile or most likely value. We will be
using the 50th percentile and comparing it to normal. At this time, the Yakima River
near Parker is expected to see about 125 to 130 percent of the 30 year normal water volume
for the period April through September. The forecasted volume of water (the blue dot)
that is expected to pass through the Grande Ronde River near Troy is currently at 105
percent of normal. The model used to produce these figures uses the current 10 days of
forecasted precipitation and assumes normal precipitation through the rest of the forecast
For the Umatilla River at Pendleton, for the period April through September, the forecast
calls for around 85 percent of normal. This lower value corresponds to the below normal
snowpack seen in the previous slides.  
The water supply point, The Columbia River at The Dalles can be an indicator for the
entire Columbia Basin. Once again we see the average plotted in green, with the most likely
value the blue dot. The volume for the April through September period expected to be just
slightly above normal. The previous seen plots are available in an interactive form on the
Northwest River Forecast Centers website at the address listed on the final slide.
  The three month outlook from the Climate Prediction
Center for January through March, shows equal chances of below or above normal temperatures
and precipitation. Thus we would expect to see near normal winter time weather through
the coming weeks with both wet and dry periods.  
Once again, additional water supply forecasts and the interactive forecasts can be found
at the Northwest River Forecast Center's Webpage at the address listed. If you have any questions,
please contact me by email or the phone number listed here.  Please join me again in February,
as we continue to assess the snowpack and the water supply forecasts for the coming