Flood Potential Outlook
Issued by NWS Portland, OR

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Water Supply Outlook
National Weather Service Portland OR
310 PM PST Monday March 5 2018


The water supply forecast for the spring and summer of 2018 is below-
average for most Oregon watersheds, especially so for the southern
half of the state. April through September runoff-volume forecasts
range from 20 to 100 percent of average, lowest in south-central
Oregon and highest in northwest and far-northeast Oregon.

Snowpack is notably low in the Cascades and all mountain ranges in
eastern Oregon. After a relatively-dry December and a relatively-
warm January, there were several storms that increased snowpack in
the latter half of February, moreso for the northern than the
southern half of the state. February was also the first month this
winter with widespread below-average temperatures in Oregon.

The March 2018 outlook by the Climate Prediction Center calls for a
enhanced likelihood of below-average temperatures and above-average
precipitation in Oregon. Looking at April through June, there are
equal chances of near, above, or below-average precipitation and
temperatures across the state. For the summer outlook, there is an
enhanced possibility of above-average temperatures. For more
details, visit www.cpc.ncep.noaa.gov.

Refer to the sections below and links provided for details regarding
snowpack, precipitation, reservoir conditions, and water supply
forecasts for individual basins.

The next update will be issued by April 4, 2018.

Snowpack across Oregon

As of early March, basin snowpack ranges from 45 to 80 percent of
average, in terms of the water content of the snow. Values are
lowest across the southern half of the state.

Weather conditions in December and January were generally not
favorable for building snowpack. However, February temperatures were
below-average statewide and precipitatinotablyon was near or a
little below-average. Basin snowpack, in terms of snow-water
equivalent percent of average, increased by 10 to 25 percent in
February. That said, seasonal totals remain below average,
especially in the southern half of the state.

Additional snowpack information:

NOAA National Weather Service - Northwest River Forecast Center

USDA Natural Resources Conservation Service

Precipitation and Temperatures across Oregon

Precipitation for the 2018 water year thus far (Oct 1, 2017 through
March 4, 2018) ranges from 70 to 100 percent of average in Oregon,
highest in northwest and far-northeast Oregon and lowest in south-
central and southeast Oregon. Temperatures in December and January
were above-average, especially at higher elevations. Temperatures in
February were 1 to 3 degrees below-average statewide.

Details on precipitation and temperatures:

NOAA National Weather Service - Northwest River Forecast Center

NOAA NWS - California-Nevada River Forecast Center (Klamath basin)


Reservoir storage as of early March is generally average to a little
above-average for this time of year and 50 to 90 percent of storage
capacity. Many reservoirs around the state have carry-over storage
from last year.

Reservoir data is provided by the Natural Resources Conservation
Service, the Bureau of Reclamation, and the US Army Corps of

Additional reservoir information:


Observed Streamflow

Observed streamflow in February 2018 varied greatly, relative to
average, around the state. In southwest and south-central Oregon,
streamflow was much below average, while in far-northeast Oregon,
streamflow was above-average. Elsewhere in the state, streamflow was
near or a little below-average.

Visit waterwatch.usgs.gov for details on observed streamflow. Water
year and monthly runoff data is available at www.nwrfc.noaa.gov for
several locations in Oregon.

Forecast Streamflow and Seasonal Runoff Volumes

Forecasts for April-September runoff volume are mostly between 50
and 85 percent of average, with some forecasts in southern Oregon as
low as 20 percent of average and some in far-northwest and far-
northeast as high as 100 percent. These forecasts are updated daily
and have generally been trending upward since mid February, moreso
for northern Oregon basins.

The forecast for the Columbia River at The Dalles, which is a good
index of conditions across the Columbia Basin, is 110 percent of
average for April-September, an increase of 3 percent from a month
ago. This forecast for The Dalles reflects above-average snowpack in
northern Washington and the Rocky Mountain portion of the Columbia
River basin.

Details on basin-scale water supply forecasts:

NOAA National Weather Service - Northwest River Forecast Center

USDA Natural Resources Conservation Service


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