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Water Supply Outlook
National Weather Service Portland OR
153 PM PST Tuesday May 7 2024

...OREGON WATER SUPPLY SUMMARY AND SPRING FLOOD OUTLOOK AS OF
MAY 7TH 2024...

The water supply forecast for the spring and summer of 2024 is near
average for watersheds for most of Oregon, with some notable
exceptions. Water supply forecasts are below average for the Klamath
basin, some watersheds in southwest Oregon, and portions of far-
northeast Oregon. Meanwhile, water supply forecasts are above
average for most of southeast Oregon. Seasonal forecasts increased
10 to 20 percent from mid April to early May for most Oregon
watersheds due to precipitation and increased mountain snowpack. The
potential for spring snowmelt flooding in northeast Oregon is low,
generally less than 5 percent. 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 flooding is highly unlikely for central and
southeast Oregon. For areas west of the Cascades, spring snowmelt
flooding has historically not occurred and is not expected this year.

Precipitation so far this water year (Oct 2023 - Apr 2024) is near
average for most of the state but above average for far-southwest
and far-southeast Oregon and below average for south-central Oregon.
Temperatures for the water year thus far are above average and
notably so for 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 last update for this water year will be issued by June 5, 2024.


PRECIPITATION AND TEMPERATURES ACROSS OREGON

Precipitation for the 2024 water year thus far (Oct 2023 - Apr 2024)
ranges from 80 to 115 percent of average in Oregon, but most
portions of the state are near average, 90 to 110 percent. The
lowest values relative to normal are in far-northeast Oregon and the
Klamath basin, and the highest are in southeast Oregon. April
precipitation was below average for all but far-southeast Oregon,
but the last week of April and first week of May saw above-average
precipitation for most of the state.

Temperatures for October through April were 1 to 4 degrees above
average for almost all of Oregon, except near normal for the
Columbia basin portion of north-central Oregon. April temperatures
ranged from 2 degrees below normal to 2 degrees above normal, with
most of the state being near normal.

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 May 5, mountain snowpack was above average for most of Oregon,
with significant increases the past 2 weeks in mid and high
elevation snow for much of the Cascades and Blue Mountains. Recent
snowpack increases have come in the midst of the typical snowmelt
season.

Snowmelt is likely to resume in earnest by May 9th and continue
through mid May with a strong likelihood of above-average
temperatures statewide.

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.

ENSO conditions have transitioned from El Nino to neutral 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 major
influence on the upcoming fall and winter.

The outlook for May through July is for an enhanced likelihood of
above-average temperatures statewide. The precipitation outlook also
indicates a slightly-enhanced likelihood for below-average
precipitation for northeast 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,
where reservoir storage ranges from 45 to 75 percent of capacity.
Most reservoirs in central and eastern Oregon have filled to
capacity. Flood control reservoirs in western Oregon are dependent
on spring precipitation and snowmelt and are in the process of
refilling as of early May, most running a little below operating
rule curves.

Owyhee Reservoir, located in southeast Oregon, is the largest
irrigation project in the state. It has observed storage of about
711,000 acre-feet, an increase of about 50,000 acre-feet from a
month ago. This is 99 percent of capacity and 133 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 areas with below-average runoff are
interior southwest, south-central and far-northeast Oregon.

Runoff in April was generally near to below average in western
Oregon, below average in far-northeast Oregon, and near average
elsewhere. There are a few notable exceptions with much-above
monthly streamflow, especially the Owyhee watershed in far-southeast
Oregon.

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 some watersheds in southwest and northeast Oregon. The
highest forecasts, relative to average, are in southeast Oregon.

The forecast for the Columbia River at The Dalles, which is a good
index of conditions across the Columbia Basin, is 77 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/

$$