Flood Potential Outlook
Issued by NWS Portland, OR

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Water Supply Outlook
National Weather Service Portland OR
1152 AM PST Monday May 6 2019

MAY 6TH 2019...

The water supply forecast for the spring and summer of 2019 is above-
average for most Oregon watersheds, with the exception of a few
watersheds in far-northwest Oregon, especially coastal basins. Major
snowpack increases in February and heavy rain in early April greatly
boosted water supply forecasts for the April-September period but
also resulted in some spring flooding across much of the state in
early to mid April. Mountain snowpack has melted rapidly since mid-
April, but additional spring flooding is unlikely.

The May 2019 outlook by the Climate Prediction Center calls for
enhanced likelihood of above-average temperatures and below-average
precipitation statewide, especially so for western Oregon.

Refer to the sections below and links provided for details regarding
snowpack, precipitation, seasonal climate outlooks, reservoirs,
streamflow, water supply forecasts, and spring flood potential.

Most of Oregon has been affected by drought for the past year, with
very low streamflow seen statewide since summer 2018, but drought
conditions have improved significantly since February. For
information about drought declarations and impacts around the state,
visit the Oregon Water Resources Department drought page at

The next update will be issued by June 4, 2019.

Precipitation and Temperatures across Oregon

Precipitation for the 2019 water year thus far (Oct 1, 2018 through
May 5, 2019) ranges from 75 to 95 percent of average in Oregon,
highest in northeast and southwest Oregon and lowest in northwest
Oregon. April precipitation was 120 to 180 percent of average, with
most of the precipitation coming in early April and dry conditions
for the latter half of the month.

Temperatures this winter prior to February were mostly above-
average, but February and March temperatures were below-average
statewide. April temperatues were near-average to 2 degrees above
average statewide.

Details on precipitation and temperatures:

NOAA National Weather Service - Northwest River Forecast Center

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

Snowpack across Oregon

As of early May, much of the mountain snowpack has melted, with some
snow still present above 4500 feet in the Cascades and above 5500
feet in central and northeast Oregon mountains. Peak seasonal
snowpack occurred in mid-March to early-April and ranged from 100 to
160 percent of average.

Additional snowpack information:

NOAA National Weather Service - Northwest River Forecast Center

USDA Natural Resources Conservation Service

Precipitation and Temperature Outlook

The Climate Prediction Center produces monthly and seasonal
outlooks, in which there is a weighing of the odds of near-normal,
above-normal, or below-normal temperatures and precipitation.

The May 2019 outlook calls for enhanced likelihood of above-average
temperatures and below-average precipitation statewide, especially
for western Oregon. The June-July-August outlook calls for enhanced
likelihood of above-average temperatures statewide, with a slightly-
enhanced likelihood of above-average precipitation in eastern

Visit www.cpc.ncep.noaa.gov for more about seasonal outlooks.


Reservoir storage as of early May is above average. Storage
increased dramatically in early and mid April due to heavy rain and
rapid snowmelt. Most reservoirs are full, although there are some
exceptions, including Hyatt, Howard Prairie, Fish Lake and Fourmile
Lake in southwest Oregon, all around 50 percent full; Wickiup and
Cresent Lake around 70 percent full in central Oregon; and Phillips
Reservoir just above 50 percent full in eastern Oregon.

Owyhee Reservoir, the largest irrigation project in the state,
increased from about 445,000 acre-feet in early April to 657,000
acre-feet in early May, about 120 percent of average for this time
of year and 92 percent of capacity.

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 runoff so far this water year is below-average for
northwest Oregon rivers, near average for southwest Oregon rivers,
and near to above-average for central and eastern Oregon rivers.
April runoff was record-high for many rivers and above-average
statewide, except for near-average in far-northwest Oregon.

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

Water supply forecasts for April-September runoff volume are
generally above-average statewide except for some watersheds in far-
northwest Oregon with below to near-average forecasts. Values range
from about 75 to 125 percent of average in northwest Oregon, 125 to
200 percent of average in west-central and southwest Oregon, and 125
to 225 percent of average for central and eastern Oregon. Forecasts
have increased dramatically in recent weeks due to the heavy rain
and snowmelt runoff in early and mid April.

The forecast for the Columbia River at The Dalles, which is a good
index of conditions across the Columbia Basin, is 92 percent of
average for April-September, reflecting near to below-average
snowpack across much of the Columbia basin. This forecast value is
an increase of 5 percent from a month ago and 27 percent lower than
this same time last year.

Details on basin-scale water supply forecasts:

NOAA National Weather Service - Northwest River Forecast Center

USDA Natural Resources Conservation Service


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