Eugene, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

704
FXUS66 KPQR 181744
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
944 AM PST Thu Dec 18 2025


.SYNOPSIS...A strong frontal system with an associated
atmospheric river will arrive early today, persisting through
the night. High confidence in widespread minor and moderate
flooding with increasing confidence in major flooding. Cascade
snow remains in the forecast as well as another round of gusty
winds. Rain persists through early next week with continued
flooding through Saturday.

&&


.SHORT TERM...Now through Friday night...The strong to potentially
extreme atmospheric river that we have been discussing the last
few days is beginning to make its steady track eastward.
Satellite shows the initial stages of the atmospheric river
moving over the Pacific Northwest this morning. Starting off as
a stratus shield, some drizzle and light rain is forming along
the coast and in the southern Willamette Valley. So far rain
rates are around 0.05 inch in an hour. This rain will intensify
as it pushes inland. Current satellite derived components of
this AR show that it currently contains around 225% of normal
precipitable water and potential blended rain rates of 0.13
inch/hr. Rain will begin to intensify around morning rush hour
traffic with heaviest amounts expected south of Marion County in
Oregon. If you live in the north, don`t let that fool you.
There will still be heavy rain, just not necessarily at the same
rate rates we have seen over the last week. This AR is going to
move much quicker than previous systems as well with the bulk
of the rain lasting around 12-18 hours; there will be continued
rain though through the weekend. Widespread flooding is forecast
and will be discussed in more detail below.

In addition to rain, wind is another concern. The surface level
plot shows a period of strong winds along the coast around 10
AM this morning with a coastal jet forming south of Tillamook.
These winds will spread inland through the late morning and
early afternoon. These winds are not necessarily front driven as
the wind that occurred on Tuesday, but rather an artifact of
the system in total. Winds at around 5000 ft are expected to be
around 60-70 mph with some models suggesting speeds up to 75
mph. Closer to the surface gusts of 45 mph will be possible. In
the case those winds are able to mix down, though this is a low
probability, high end winds could reach as high as 60 mph along
the coast, 40-50 mph within the valley, and around 60 mph at
higher elevations. An inhibiting factor for those speeds is that
this system is not convective. This fact makes it significantly
more difficult to tap into these winds. As it stands though,
there is enough confidence to issue a Wind Advisory for the
Coast Range, Willamette Valley and the foothills of the
Cascades. A High Wind Warning is also in effect for the coastal
areas. A component to consider is that even if speeds do not
necessarily reach exceptional speeds, the ample rain from
previous days and more abnormal direction (south to
southwesterly) will make tree damage more likely leading to
blocked roadways and power outages. These strong winds will
dissipate after the bulk of the AR passes tonight.

Now who is ready to talk about snow? Snow levels are currently
around 3000 ft and will linger there for a few more hours.
Precipitation is beginning to fall as snow but overall is fairly
light. As this system takes control of the region, snow levels
will rise considerably and therefore the Cascades will
experience only rain. This rain will likely erode some of the
snow that has fallen over the previous days. Hope is not lost
though as cold air will trickle in behind the system from north
to south. Snow levels will drop to around 2000 ft Friday morning
north of Santiam Pass on Friday. Further south, the remnants of
the AR may keep temperatures slightly too warm for widespread
snow but would see it along the peaks and potentially at the
passes. For our winter sports enthusiasts, it`s not time to get
too excited as precipitation during this time will be much less
than on Thursday and therefore wildly impactful snow is not
expected. -27

.LONG TERM...Saturday through Wednesday...Much more settled
weather this weekend into early next week. The remnants from the
atmospheric river will linger through Saturday with showers
persisting through the day. Accumulation will be light and more
typical for this time of year. Areas that will receive the most
precipitation will be along the coast and the south Washington
Cascades where up to an inch is possible through Sunday.

On Sunday night into Monday, a low pressure system near
Vancouver Island will remain nearly stationary pushing what
appears to be a shortwave over the area. Some models suggest
another closed low could form at the base of that trough which
would cause a surge of precipitation, but at this point
confidence is incredibly low due to the messy nature of the
pattern. If this this closed low comes to fruition cannot rule
out an evening of breezy winds Monday into Tuesday but again,
until it`s better realized there are no major concerns at this
point. -27

&&

.AVIATION...The atmospheric river will continue to push inland
this morning and winds will continue to increase, with lowering
ceilings, and precipitation. Look for steadily degrading
conditions this morning. The strongest wind and heaviest rain
are expected between about 18-20Z to 03-06Z. There is a 10%
chance of gusts as high as 55 kt along the coast, especially
around KONP, around 40 kt from KCVO south in the Willamette
Valley, 35 kt around KPDX, and over the Cascades as high as 60
kt. LLWS is expected with a low level jet forming between
2000-5000 ft AGL. At the upper end of that range gusts up to 70
kt are possible. At the surface winds will be strongly
southwesterly. VIS will drop significantly with these types of
speeds and heavy rain.

As the system dissipates towards the end of the forecast period
will see VIS improve but CIGs will be a bit more difficult to
see significant changes, but models only hold on about 20-30%
chance of MVFR conditions or worse in some TAF sites, so some
improvement is possible for time between 09-13Z. Rain will
persist though will become lighter after 06Z Fri.

KPDX AND APPROACHES...Main impact will be wind and VIS due to
heavy rain. Winds will fluctuate through the day with peak winds
occurring between 20Z Thu through 06Z Fri.

&&

.MARINE...Winds have been a bit slower to respond this morning
as the atmospheric river sits well offshore. However, once they
start to increase we will see a drastic intensification of
speeds. Due to a coastal jet forming along the central and
southern waters, a Storm Warning has been issued for low-end
wind speeds. There is currently around a 10% chance of gusts as
high as 55 kt, but confidence is incredibly low for that to
occur. Instead, the most likely scenario are gusts around 48-50
kt. Seas too will build with a longer westerly fetch and a
strong southerly wind wave. Because these two sea states are not
well aligned, we will struggle to see seas grow above 20 ft.
There is around a 25% chance of seas greater than 18 ft.

As the system shifts inland winds will quickly ease and wind
waves will follow suit. The dynamic westerly swell though will
remain due to a nearly stationary system in the northeast
Pacific. Through the weekend will see few changes. -27


&&

.HYDROLOGY...Today through Friday will be heads-up days in
regards to river flooding due to the abundant rainfall from a
strong atmospheric river. Heaviest rainfall occurs for a
relatively short period of time through tonight. Due to already
saturated soils and swollen rivers from previous rain, rivers
will be more prone to experience flooding. As is typical in
atmospheric rivers, the highest rainfall totals are likely to be
over areas of terrain including the Coast Range and Cascades,
while lesser totals can be expected across inland valleys.
Nonetheless, rainfall is likely to be measured in inches across
most of the region. High rain rates this afternoon will promote
urban and small stream flooding though where that will occur is
uncertain. It`s important to watch your surroundings as urban
flooding can come upon quickly and without notice. One
difference between the last series of ARs and today`s event is
the placement of highest rainfall totals. This next system
favors a more southern maximum, and thus areas that previously
missed the heaviest rain will see the higher accumulations this
time around.

Due to the lack of observed rain, particularly in Lane County,
some basins will be more capable of handling heavy rainfall
without experiencing flooding. Other areas to the north within
the Coast Range in Lincoln, Tillamook, Benton, Polk, Yamhill,
and Washington Counties may see more overlap between recently
observed heavy rainfall and additional high totals with this
upcoming system. Similarly, river basins covering the central OR
Cascades in Lane and Linn Counties may have a slightly more
optimistic outlook than north into Marion and Clackamas
Counties, but that does not mean flooding cannot happen in all
of the aforementioned areas.

Based on recent forecasts, there will be widespread flooding
with four rivers forecast to reach major flood state, six to
reach moderate, and more than ten to reach minor flood stage. At
this point, the rivers with the highest chances of reaching
flood stage are those which drain the central Oregon Coast
Range, including the Wilson, Trask, Siletz, and Siuslaw draining
toward the coast, and the Marys, Luckiamute, Yamhill, and
Tualatin draining toward the Willamette. The chances for these
rivers to reach at least Minor flood stage are 35-75% at this
time. Those draining toward the coast, particularly in Lincoln
and Lane Counties where rainfall is likely to continue later
into Friday may see minor tidal overflow as rivers crests
coincide with high tide on Friday, though this occurrence
remains lower confidence. Rivers draining the Cascades,
including the Mohawk, Santiam, Pudding, Molalla, Clackamas, and
Sandy, have increased with chances of 25- 90%. These rivers will
begin to rise later on Thursday as heavy rain continues, not
cresting until Friday in most cases. Latest forecasts have
introduced multiple floods reaching moderate to major flood
stage, including the Molalla River near Canby, Clackamas River
near Estacada, and the Johnson Creek near Sycamore. There is
also potential for the Clackamas near River near Oregon City to
reach record stages if latest rainfall forecasts remain on
track.

The Willamette River main stem itself has a 5-10% chance of
reaching flood stage above Willamette Falls, and slightly higher
chances in tidally-influenced portions downstream of Oregon
City, however runoff will take longer to reach the Willamette
and flooding would be delayed later than in its tributaries. A
Flood Watch remains in effect across all of northwestern Oregon
and southwestern Washington from through 4 PM Saturday to
highlight these risks. Note that the watch has been extended to
encapsulate areas that may be slower to respond.

These river forecasts remain very sensitive to rainfall
forecasts, and interested parties should expect changes as the
event nears. The latest river forecasts across the region can be
found at www.water.noaa.gov/wfo/pqr.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Coastal Flood Advisory from 8 AM this morning to 4 PM PST this
     afternoon for ORZ101>103.
     High Wind Warning from 8 AM this morning to 7 PM PST this
     evening for ORZ103-107.
     Wind Advisory from 8 AM this morning to 7 PM PST this evening
     for ORZ104>106-108>118-123>125.
     Winter Weather Advisory until 10 AM PST this morning for
     ORZ121-126-127.
WA...Coastal Flood Advisory from 8 AM this morning to 4 PM PST this
     afternoon for WAZ201.
     Wind Advisory from 8 AM this morning to 7 PM PST this evening
     for WAZ202>208.
     Winter Weather Advisory until 10 AM PST this morning for
     WAZ211.
PZ...Hazardous Seas Warning until 4 AM PST early this morning for
     PZZ210-251>253-271>273.
     Gale Warning until 10 PM PST this evening for PZZ210-251-271.
     Storm Warning until 10 PM PST this evening for PZZ252-253-272-
     273.
&&

$$

www.weather.gov/portland

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