Hydrologic Outlook issued December 27 at 2:58AM PST by NWS Portland OR

ESFPQR

A series of storm systems will continue to bring a wet weather
pattern across northwest Oregon through the weekend. This will lead
to rises on rivers and creeks through at least December 30th. There
is currently a 30-50% chance that several rivers in northwest Oregon
will reach minor flood stage over the next 10 days, including: the
Wilson River, Siletz River, Tualatin River, Siuslaw River, Marys
Rivers, and the Pudding River. The Luckiamute River has the highest
chance of hitting minor flood stage at 85%. In addition, there is a
20-25% chance the Nehalem River, Trask River, Yamhill River and
Mohawk River will reach minor flood stage.

Heavy rainfall may also lead to ponding of water, general lowland
flooding and localized urban flooding, especially in low lying areas
or other areas with poor drainage. Heavy rainfall will also increase
the potential for landslides in areas of steep terrain and debris
flows over areas that have been burned by wildfires over the past
few years.

There is still some uncertainty regarding the exact track of these
upcoming storm systems and associated rain amounts. There is
currently a 10% chance the southern Willamette Valley will receive
2-3″ of rain and the adjacent higher terrain of the Coast Range and
Cascades will receive 3-5″ of rain Saturday evening through Sunday
morning. This represents the worst case scenario, which would result
in more widespread flooding issues. That said, the most likely
scenario is 1-2″ of rain in the southern Willamette Valley and 2-3″
in the adjacent higher terrain of the Coast Range and Cascades. This
would result in minor and less widespread flooding. Shifts in the
forecast storm track can change the current outlook, so be sure to
monitor weather.gov/portland for the latest weather updates, as well
as any watches, warnings, or advisories that may be issued. To view
the latest river forecasts, visit water.noaa.gov/wfo/pqr.