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This is Marilyn Lohmann, Service Hydrologist at WFO Pendleton. I will be reviewing the
mountain snowpack over the last month and the water supply forecasts for the coming
months. 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.
February was a very stormy month with a large increase in the snowpack and precipitation
across the region. Snowpack in the central and southern Washington Cascades increased
from near 60 percent of normal to slightly above normal with amounts near 105 percent
of normal. In southeast Washington the snow water equivalent increased from 85 percent
of normal to 114 percent of normal. We will look at a few locations within the basins
to see how the snowpack changed over the last month.
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. Looking at the black line, we can see that this site had a steady accumulation during
the month, but remains slightly below normal. The Sasse Ridge Snotel site is located in
the Upper Yakima Basin at 4200 feet. This site saw a large increase during the month
of February and is now near normal. The Bumping Ridge Snotel, elevation 4600 feet
is in the Central Washington Cascades. Looking at the black line, we can see there was a
large increase throughout the month, with amounts near normal.
Across the Oregon, there were some good increases as well, but as you can see on this graphic
from March 4th , the snowpack is still below normal over most of the state. Amounts increased
from around 20 to 30 percent of normal over the Cascades to near 60 percent of normal.
The John Day Basin increased from around 50 percent of normal last month to near 70 percent
of normal. The Umatilla Basin and Grande Ronde Basin ranged from 70 to 75 percent of normal
at the start of February and have improved to near 85 to 95 percent of normal. We will
look at some individual sites within the basins in the next several slides.
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, there was a large increase, but
still remains well 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 had a modest increase through the month, but remains well below normal.
For the John Day Basin, we can look at the Blue Mountain Springs Site at 5900 feet. This
location had a substantial increase through the month, however it still continues to be
below normal. For the Umatilla basin in 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 through the month and is slightly below normal.
In the Grande Ronde Basin, the Moss Springs Snotel Site at 5800 feet continues to show
a good accumulations of snow and has increased to above normal.
The Northwest River Forecast Center uses Ensemble Streamflow Prediction or ESP generated forecasts
as the official water supply method. The 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 my be updated daily as the discretion of the NWRFC. For updated forecasts and a
more information of ESP forecasts, please see the river forecast centers website at
the address given. This map from the Northwest River Forecast
Center shows a snapshot of the water supply forecasts for the coming season. There has
been a fairly good improvement in the water supply expected across the region. Locations
in Washington that were expected to see supplies 75 to 90 percent of normal are now expected
to see near normal conditions, with above normal water supply expected in northern Idaho
and Montana. Across Oregon, the northern portions have improved but the southern portions of
the state are still expecting below normal amounts, with the well below normal amounts
extending into the Snake River area of Southern Idaho.
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. The volume forecast for, the Yakima
River near Parker has continues to show an increase over the last month. Water supply
amounts are now expected to be near 120 percent of normal.
The forecasted volume of water (the blue dot) for the Grande Ronde River near Troy has increased
some and is expected to be slightly above normal at 115 percent.
For the Umatilla River at Pendleton, for the period April through September, the volume
forecast has increased slightly and is between 85 to 90 percent of normal.
For the site The Columbia River at The Dalles,
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 has increased from around 90 percent of normal
at the start of February to near 100 percent of normal. The previous seen plots and additional
water supply locations are available in an interactive form on the Northwest River Forecast
Centers website at the address listed on the concluding slide.
The three month outlook from the Climate Prediction
Center for March, April and May calls for near to above normal temperatures and equal
chances for above or below normal precipitation. For more information on the unseasonably dry
and drought conditions both here in the Northwest and across the country, please visit the National
Integrated Drought Information System webpage at the address above. You can view the Drought
Monitor, look at current and forecast conditions as well as impacts from drought and also find
resources relating to drought. 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. Please join me again in early April to see how the snowpack is
progressing and updated water supply forecasts. If you have any questions, please contact
me by email or the phone number listed here.