Beaverton, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

791
FXUS66 KPQR 162339
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
339 PM PST Tue Dec 16 2025

.SYNOPSIS...Very active weather continues with repeated frontal
systems bringing heavy rain, gusty winds, flooding, and even
some Cascade snow through the remainder of the week.
Confidence is highest in strong wind chances tonight into early
Wednesday, and for heavy rain and flooding Thursday and Friday.

&&

.SHORT TERM...Now through Wednesday Night...Respites from active
weather will be brief through much of the next week. An area of
earlier light rain as exited to the north/east of the region,
but an impressively potent shortwave will approach and pass
overhead late this evening through midday Wednesday. As this
wave moves onshore, a surface low will track north of Vancouver
Island while a strong trailing cold front affects areas well to
its south. A low-level jet of 50-70 kt at 925 hPa ahead of this
cold front will increase the chances of strong winds reaching
the surface through tonight as the jet makes its closest
approach. Low heights aloft within the frontal trough will
support at least shallow convection, which may both generate
isolated thunderstorms as well as mix down the high momentum air
from not too far off the surface.

Locations along the immediate coast will be most susceptible to
the strongest winds, with gusts possibly exceeding 60 mph
through tonight. Areas just inland from the coast as well as
areas of higher terrain including the Coast Range, Willapa
Hills, Cascades and foothills will also be more likely to see
stronger wind gusts of 50-55 mph. A High Wind Warning therefore
remains in effect for the coast and Wind Advisories for other
aforementioned locations through 6 AM Wednesday. Within inland
valleys, conditions will also certainly be breezy, however
confidence in frequent or widespread gusts to 40-45 mph or more
is lower. Downslope effects as the jet passes over the Coast
Range and any convection may aid in generating locally stronger
winds, but widespread damaging gusts seem less likely than other
areas. The correlation of the high wind threat with possible
thunderstorms has also merited a Marginal Outlook for severe
wind gusts from the Storm Prediction Center. While these storms
may not match the theoretical dynamics associated with severe
weather, any cell deep enough to generate lightning will also be
deep enough to interact with the low-level jet.

This front will also bring another round of rain beginning this
evening, becoming heavier and more widespread tonight, before
winding down through Wednesday afternoon. Given the relatively
short duration of precipitation, rainfall amounts are not
excessive. Most likely totals will range from 0.25-1.0" along
the I-5 corridor, 0.5-2.0" along the coast and within the Coast
Range, and 1-3" within the Cascades and foothills. While area
rivers are very likely to rise in response to this rain, none
are forecast to reach flood stage in the next 36 hours. Behind
the progressive cold front, snow levels will drop precipitously
from 6000-7000 ft this evening down to 2000-3000 ft by early
Wednesday morning. As most of the precipitation should fall
ahead of the boundary, high-terrain snow totals remain fairly
low. The south Washington Cascades along with the high peaks of
the Oregon Cascades may see totals above 6-12", but closer to
pass elevations, totals of 3-6" are more likely. A Winter
Weather Advisory therefore remains in effect across the south
Washington Cascades from 10 PM this evening through 10 PM
Wednesday. While strong winds are also expected within the
Advisory area, the relatively wet snow character may limit the
risk of lofting and blowing snow impacting visibility. There is
a 10% chance snow levels fall below 1800-2000 ft, in which case
totals of 8-12" at pass-level may occur. Temperatures are also
expected to quickly fall below freezing at pass-level as the
front passes, which may result in any wet roads becoming slick
after about 3-5 AM. Early morning travelers over the Cascades
should keep an eye out for black ice. -36


.LONG TERM...Thursday through Tuesday...The latter portion of
the workweek will feature another potent atmospheric river over
the Pacific Northwest. Based on forecast vapor transport, the
upcoming AR would be classified as strong to extreme, however
caution should be used if trying to tie those labels to
potential impacts. Unlike the AR which affected western
Washington last week, this system is more likely to produce
higher rain totals farther to the south in western Oregon, and
its duration is also likely to remain shorter, limiting the
chances for more extreme high-end rainfall amounts. Nonetheless,
well above normal rainfall amounts through the first half of
December across most of northwestern Oregon have primed the area
for potential flooding even with lesser rainfall totals. The
exception may be for Lane County, where considerably less rain
has fallen in recent weeks yielding soils are farther from
saturation. Thursday through Thursday night, rainfall rates may
initially post a threat for urban or small stream flooding,
especially in areas farther north nearer the Columbia River
where soils remain wet. To the south, higher or more persistent
rain rates may be needed to yield this sort of flooding, but the
risk remains regardless. The Thursday evening commute is the
most likely to be affected by roadways with standing water,
although impacts may linger into the Friday morning commute
south of US-20.

Overall, as is typical with ARs, the highest precipitation
totals are likely to be over the coastal terrain and across the
Cascades, and the warm dynamics will also favor increasing snow
levels during the heaviest precipitation. While the details of
the precipitation forecast may change slightly from update to
update, the consensus remains that the highest totals will fall
in the Coast Range and Cascades south of US-26. Most likely
48-hour rainfall amounts from 4 AM Thursday to 4 AM Saturday
will increase from north to south across the region, from
around 2" around Kelso/Longview and Portland/Vancouver, around
3" near Salem, and around 4" near Eugene, with similar values at
coastal cities. In higher terrain, 4-8" is more likely, while
even higher-end amounts of 8-10" may very well be observed
somewhere across these areas. River forecast remain very
sensitive to these details of the precipitation distribution,
and specific drainages which are most likely to see higher
floods may not be apparent until the event is well underway. At
this point, a number of rivers draining the Coast Range and
Cascades are forecast to reach either Minor or Moderate flood.
As runoff moves downstream, even the main stem of the Willamette
River has some risk of reaching flood stage late in the week,
about a 5-10% chance. Some larger rivers draining to the coasts
of Lincoln and Lane County will also be the most likely to see
tidal overflow if river crests occur near high tide. Further
detail can be found in the Hydrology discussion below.

As snow levels again fall below 3500 ft, chances for
accumulating pass-level snow in the Cascades increases Friday
into the weekend, however with the bulk of precipitation on the
warm side of the front, significant accumulations are not
anticipated. As moist zonal flow then continues through the
weekend, persistent lowland rain and high elevations snow
chances also continue. While the detail remain relative low
confidence, current long-range guidance does not favor another
high-end rainfall event through the middle of next week. -36

&&

.AVIATION...Radar imagery as of late Tuesday morning show light
showers approaching the coast as the next system approaches the
area. Terminal observations show VFR CIGs across the Willamette
Valley and MVFR CIGs at KAST and LIFR CIGs at KONP. The next
frontal system will increase rainfall across the region after
00z  Wednesday. This frontal system is more robust than the
rain showers from this morning. Tonight, there is high
confidence (>80% chance) for IFR CIGs or lower and moderate
confidence (40-60% chance) for MVFR CIGs across Valley
terminals. The environment will be convective, so there is also
a 15-20% chance of thunderstorms over the coast, Coast Range and
some of the interior terminals. These chances generally
increase after 00Z Wed and persist through 12z Wed. Heavy rain
from thunderstorms may briefly drop CIGs/VIS to IFR thresholds
or lower at any terminal. Guidance suggests widespread
improvement to VFR across the region after 12-15z Wed.

Wind is also becoming more of a concern over the next 24 hours.
Around 00Z Wednesday, along with the passage of the front, south
to southwesterly winds will begin to ramp up not only at the
surface but aloft. Could see surface gusts up to 40-45 kt along
the coast and 25-30 kt across the Valley overnight. Around 2000
ft, guidance suggests strong southwesterly winds up to 50 kt.
This will lead potentially strong cross winds for E-W aligned
runways. Added LLWS for inland terminals between 05-09z Wed, but
shear should be unidirectional.

KPDX AND APPROACHES...Predominately VFR through this afternoon.
After 00z Wed, there is a 30-50% chance for MVFR CIGs and a 5%
chance for southwesterly wind gusts exceeding 45 kt. Southwest
winds likely gust around 25-30 kt from 00-12z Wed with the next
front. CIGs improve to predominately VFR after 12z Wed. -10

&&

.MARINE...Observations at buoy 46029 and 46060 as of late
Tuesday afternoon show southerly winds with gusts up to 25 kt
and seas hovering around 10-12 ft at 11-12 sec. This brief lull
will end later this afternoon when another frontal system
approaches the waters. This will return breezy south-
southwesterly winds with widespread gusts ramping up to 35-40 kt
this afternoon and evening, and peaking around 40-45 kt
overnight. For the inner waters out 10 NM including the Columbia
River Bar, there is also a 20-50% chance for maximum wind gusts
exceeding 48 kt (storm force) due to a coastal jet, with the
highest chances between Cape Falcon and Cape Foulweather. Any
gusts of this magnitude would be isolated and brief in nature;
therefore, there is not enough confidence to warrant a Storm
Warning. Instead, Gale Warnings are in effect from 4 PM this
afternoon through 10 AM Wednesday across all waters including
the Columbia River Bar. Behind the front, winds turn westerly
after 10 PM tonight. Seas also re-build to 14-17 ft this evening
and peak around 18-20 ft at 11-12 ft tonight into Wednesday
morning as a westerly swell increases. Chances for seas
exceeding 20 ft are around 20-30%, with the highest chances
north of Cape Falcon.

Winds gradually ease after 4 AM Wednesday and seas should begin
to subside between 10 AM-1 PM Wednesday. High confidence (>80%
chance) seas fall below 15 ft by Wednesday evening. Another
atmospheric river arrives Thursday-Friday, swinging another
strong front that may bring another round of Gales (60-70%
chance), with the highest chances south of Cape Falcon as this
system is progressing toward central and southern Oregon. -10

&&

.HYDROLOGY...Potential for river flooding is highest on
Thursday and Friday due to the abundant rainfall from an
atmospheric river. Heaviest rainfall occurs for a relatively
short period of time from Thursday through Thursday night. The
already saturated soils and high rivers combined with the
incoming well above normal rainfall has resulted in an elevated
risk for flooding late this week. 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. One difference between the last series of ARs and the
one arriving on Thursday 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. Luckily, where rainfall has so far
been the heaviest across southwestern Washington and far
northwestern Oregon may see the lowest totals from this system,
although even 1-2 inches of rain over 24 hours may be enough to
cause additional flooding in these very saturated areas.

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 30-70% 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 slightly lower but still significant chances of
15-45%. These rivers will begin to rise later on Thursday as
heavy rain continues, not cresting until Friday in most cases.
The Willamette River main stem itself also 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 4 AM
Thursday through 4 AM Saturday to highlight these risks.

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. -36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Wind Warning until 6 AM PST Wednesday for ORZ101>103.

     Wind Advisory until 6 AM PST Wednesday for ORZ104>107-123>125.

WA...High Wind Warning until 6 AM PST Wednesday for WAZ201.

     Wind Advisory until 6 AM PST Wednesday for WAZ202-203-208.

     Winter Weather Advisory from 10 PM this evening to 10 PM PST
     Wednesday for WAZ211.

PZ...Gale Warning until 10 AM PST Wednesday for PZZ210-251>253-
     271>273.

     Hazardous Seas Warning from 10 AM to 10 PM PST Wednesday for
     PZZ210-251>253-271>273.

&&

$$

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