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Flood Potential Outlook
Issued by NWS Portland, OR

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FGUS76 KPQR 032301
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Water Supply Outlook
National Weather Service Portland OR
400 PM PST Wednesday April 3 2024

...OREGON WATER SUPPLY SUMMARY AND SPRING FLOOD OUTLOOK AS OF
APRIL 3RD 2024...

The water supply forecast for the spring and summer of 2024 is near
average for watersheds in the Cascades and most of northeast Oregon,
below average for the Klamath basin and most of western Oregon, and
above average for some watersheds in east-central and southeast
Oregon. Forecasts declined 10 to 20 percent for most watersheds in
western Oregon and the Klamath basin. There was a mix of increases
and decreases for forecasts for much of central and eastern Oregon.
Water supply forecasts may evolve significantly through April. The
potential for spring snowmelt flooding is low, generally 10 to 30
percent, for watersheds in central and northeast Oregon. Any
flooding that occurs would likely be caused by either a period of
much-above average temperatures or a combination of above-average
temperatures and moderate to heavy precipitation. Spring snowmelt
flooding has historically not occurred along rivers west of the
Cascades and is not expected this year.

Precipitation so far this water year (Oct 2023 - Mar 2024) is near
average for most of the state but above average for coastal portions
of southwest and southeast Oregon. Temperatures for the water year
thus far are above average and notably so portions of northeast and
south-central Oregon.

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

The next update to this outlook will be issued by May 6, 2024.


PRECIPITATION AND TEMPERATURES ACROSS OREGON

Precipitation for the 2024 water year thus far (Oct 2023 - Mar 2024)
ranges from 75 to 115 percent of average in Oregon, but most
portions of the state are near average, 90 to 110 percent. The
lowest values are in far-northeast Oregon and the Klamath basin, and
the highest are in southeast Oregon. March precipitation was above
average for most of the southern half of Oregon and coastal portions
of northwest Oregon and below average for most of the northern half
of Oregon.

Temperatures for October through March were 1 to 4 degrees above
average for almost all of Oregon, except near normal for the
Columbia basin portion of north-central Oregon. March temperatures
were 1 to 4 degrees below normal for the southern half of the state
and near average for the northern half of the state.

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

Westwide Drought Tracker Precipitation & Temperature graphics
wrcc.dri.edu/wwdt/index.php?region=or


SNOWPACK ACROSS OREGON

As of April 1, mountain snowpack was above average for most of
Oregon, with basin snowpack ranging from 85 to 125 percent of
average. The highest totals relative to average are across the
southern third of the state, and the lowest totals in far-northeast
Oregon. Snowpack in the Cascades is generally above average north
and below average south. Snowpack increased notably in the first
half of March, with significant snowmelt in late March.

Additional mountain snow is possible through April, but the snowmelt
season that began in late March has continued in early April and is
likely continue through April, with brief interruptions due to
cooler temperatures and mountain snow. Oregon snowpack typically
melts out between early May and early June.

Additional snowpack information:

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

USDA Natural Resources Conservation Service
nwcc-apps.sc.egov.usda.gov/imap/


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.

El Nino conditions are moderate through the spring and expected to
be transition to ENSO neutral by early summer and are likely to
transition to La Nina by autumn 2024. ENSO conditions have a minimal
impact on summer conditions but will likely have a strong influence
on the upcoming fall and winter.

The outlook for April through June is for an enhanced likelihood of
above-average temperatures. The precipitation outlook also indicates
a slightly-enhanced likelihood for below-average precipitation for
northwest Oregon, with equal chances of near, above, or below
average elsewhere. The outlook for the likelihood of above-average
temperatures and below-average precipitation continues through the
summer.

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


RESERVOIRS

Reservoir storage for most irrigation reservoirs across the state is
generally above average, with the exception of southwest Oregon.
Reservoir storage ranges from about 50 to 100 percent of capacity.
Notably, most reservoirs in central and eastern Oregon have filled
to capacity. Flood control reservoirs in western Oregon are
dependent on spring precipitation and snowmelt to refill March
through May, and most are currently refilling a little behind the
rule curve schedules.

Owyhee Reservoir, the largest irrigation project in the state, has
observed storage of about 660,000 acre-feet, an increase of 124,000
acre-feet from a month ago. This is 92 percent of capacity and 131
percent of average for this time of year.

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


OBSERVED STREAMFLOW

Observed runoff so far this water year has been above average for
most watersheds statewide, particularly so for watersheds in central
and southwest Oregon. The only area with below-average runoff is
south-central and interior southwest Oregon.

Runoff in March was generally near to above average statewide, but
above average for coastal portions of western Oregon and below
average for watersheds in the Klamath basin.

Visit waterwatch.usgs.gov for details on observed streamflow. Runoff
data is available at www.nwrfc.noaa.gov/natural/index.html at water
year and monthly time scales for several locations in Oregon.


WATER SUPPLY SEASONAL FORECASTS

Water supply forecasts for April-September runoff volume are near to
above average for most of the state, except for below-average
forecasts for watersheds in west-central and northwest Oregon and
within the Klamath basin in south-central Oregon. The highest
forecasts, relative to average, are in central and east-central
Oregon.

The forecast for the Columbia River at The Dalles, which is a good
index of conditions across the Columbia Basin, is 81 percent of
average for April-September.

Details on basin-scale water supply forecasts:

NOAA NWS - Northwest River Forecast Center
www.nwrfc.noaa.gov/ws/

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

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

$$