Flood Potential Outlook
Issued by NWS Portland, OR

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Water Supply Outlook
National Weather Service Portland OR
915 AM PST Wednesday March 6 2019

...OREGON WATER SUPPLY AND SPRING FLOOD POTENTIAL OUTLOOK AS OF
MARCH 6TH 2019...

The water supply forecast for the spring and summer of 2019 is near-
average for most Oregon watersheds. Exceptions are some above-
average forecasts in central and northeast Oregon and some below-
average forecasts in northwest and far-southeast Oregon. Cold
temperatures and ample snowfall in February resulted in increases in
all water supply forecast volumes in Oregon compared to a month ago.
The increased snowpack also raises concerns somewhat about the
potential for spring flooding in central and eastern Oregon,
although the threat of snowmelt-related flooding remains low.

The March 2019 outlook by the Climate Prediction Center calls for
enhanced likelihood of below-average temperatures statewide,
especially for the first half of the month. For precipitation, there
is enhanced likelihood of above-average in southern Oregon, with
equal chances of near, below, or above-average precipitation for
northern 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. Drought
conditions remain but have improved significantly since late
January. For information about drought declarations and impacts
around the state, visit the Oregon Water Resources Department
drought page at www.oregon.gov/owrd/pages/wr.drought.gov.

The next update will be issued by April 5, 2019.

============================================================
Precipitation and Temperatures across Oregon

Precipitation for the 2019 water year thus far (Oct 1, 2018 through
March 4, 2019) ranges from 75 to 100 percent of average in Oregon,
highest in northeast and southwest Oregon and lowest in northwest
Oregon. Precipitation during February was 150 to 200 percent of
average for most of the state, with the exception of 120 to 150
percent of average in northwest Oregon.

Temperatures this winter prior to February were predominantly above-
average, but there was an abrupt change in February, with
temperatures across Oregon 5 to 8 degrees below average and
relatively low freezing levels through the month.

Details on precipitation and temperatures:

NOAA National Weather Service - Northwest River Forecast Center
www.nwrfc.noaa.gov/water_supply/wy_summary/wy_summary.php

NOAA NWS - California-Nevada River Forecast Center (Klamath basin)
www.cnrfc.noaa.gov/water_resources_update.php

===================================================================
Snowpack across Oregon

As of early March, basin snowpack ranges from 90 to 150 percent of
average, in terms of the water content of the snow. This is a major
increase from late January, when basin snowpack ranged from 50 to
105 percent of average. Snow-water content relative to average is
lowest for northwest Oregon, especially in the north Cascades near
Mt. Hood and Mt. Jefferson, and highest in the Blue and Wallowa
Mountains of eastern Oregon.

Weather conditions November through January were not favorable for
building snowpack, with above-average temperatures and below-average
precipitation. However, February was an abrupt change to cold and
wet conditions, changing the snowpack condition from below to above
average in just a few weeks.

Additional snowpack information:

NOAA National Weather Service - Northwest River Forecast Center
www.nwrfc.noaa.gov/snow/

USDA Natural Resources Conservation Service
www.nrcs.usda.gov/wps/portal/nrcs/main/or/snow/

===================================================================
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 March outlook from the Climate Prediction Center calls for
enhanced likelihood of below-average temperatures statewide,
especially for the first half of the month. The outlook for
precipitation indicates an enhanced likelihood of above-average
precipitation in southern Oregon, with equal chances of near, below,
or above-average precipitation for northern Oregon.

The outlook for April through June calls for enhanced likelihood of
above-average temperatures, with equal chances of near, above,
or below-average precipitation statewide.

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

===================================================================
Reservoirs

Reservoir storage as of early March is below average, generally 30
to 80 percent of average for this time of year and 20 to 80 percent
of capacity. The major increases in mountain snowpack statewide
during February have improved prospects for at least some irrigation
reservoirs to fill later this spring. For Corps of Engineers
reservoirs in the Willamette basin, the refill season started in
early February. Most Willamette projects are filling slower than the
refill curve. Spring precipitation will have a big impact on them
filling by the end of May.

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

Additional reservoir information:

www.wcc.nrcs.usda.gov/basin.html
www.usbr.gov/pn/hydromet/select.html
www.nwd-wc.usace.army.mil/nwp/teacup/willamette/

===================================================================
Observed Streamflow

Observed streamflow so far this water year is below-average,
generally 45 to 80 percent in terms of runoff volume October 2018
through February 2019. The lowest values relative to normal are in
northwest Oregon and portions of southeast Oregon. The below-average
runoff so far this water year is caused by overall below-average
precipitation along with a lack of heavy-precipitation events
causing major rises on rivers during the winter.

Looking more recently at the past four weeks, streamflow was near-
average for rivers draining lower-elevation areas and below-average
for rivers draining higher-elevation areas, where most of the
precipitation in February fell as snow and didn`t produce much
runoff.

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 range from
about 65 to 110 percent of average in western Oregon and far
southeast Oregon and 100 to 140 percent of average in central and
eastern Oregon, highest in far-northeast Oregon. These forecasts
represent a major increase from a month ago, anywhere from 10 to 40
percent of average, due to the above-average precipitation and major
increases in mountain snowpack in February.

The forecast for the Columbia River at The Dalles, which is a good
index of conditions across the Columbia Basin, is 87 percent of
average for April-September, reflecting near to below-average
snowpack across much of the Columbia basin. This forecast value is
unchanged from a month ago and is 23 percent lower than this same
time last year.

Details on basin-scale water supply forecasts:

NOAA National Weather Service - Northwest River Forecast Center
www.nwrfc.noaa.gov/ws/

USDA Natural Resources Conservation Service
www.wcc.nrcs.usda.gov/wsf/

============================================================
Spring Flood Potential

The potential for flooding along rivers in central and eastern
Oregon is low despite the recent increases in mountain snowpack. In
northeast Oregon (Blue and Wallowa Mountains), there is a slightly
elevated risk of spring flooding due to higher than normal snowpack
as of early March. Accumulated snow at lower elevations in northeast
Oregon also adds to the slightly elevated risk. However, there is no
indication of an imminent rapid warm-up or heavy precipitation that
would result in flooding. This is something to monitor through the
spring.

Historically, the frequency of spring flooding east of the Cascades
is low, but when it does occur, it typically involves a combination
of snowmelt and rainfall runoff. Snowmelt-driven spring flooding
doesn`t occur in western Oregon. Stay tuned to snowpack conditions
and streamflow forecasts at www.nwrfc.noaa.gov.


Bryant
$$


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