872
FXUS66 KPQR 222345
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
345 PM PST Sat Feb 22 2025

.SYNOPSIS...Active weather through early next week as a
moderate to strong atmospheric river and multiple frontal
systems bring moderate to heavy rain and periods of strong winds
to the area today through Monday. Greatest flood concerns for
coastal rivers, with ponding of water and rises of creeks and
streams as the main concern inland. Quieter conditions expected
mid to late next week.

&&

.SHORT TERM...Saturday Afternoon through Monday Night...Visible
satellite imagery this afternoon shows a very clear picture of
the atmospheric river approaching the Pacific Northwest with a
stream of moisture and clouds stretching all the way from the
coast out through the Pacific Ocean to west of Hawaii. Multiple
frontal systems will move through the region through Monday,
bringing multiple rounds of precipitation associated with the
atmospheric river. The warm front associated with the first
frontal system moved inland this morning and brought a round of
rain to the area, which is increasing over the Cascades this
afternoon. The stronger cold front is currently moving onshore
along the coast, bringing the first round of widespread
moderate to heavy rainfall tonight into tomorrow. Expect
rainfall totals from this evening through Sunday morning to
range from 1.25-2.50 inches for coastal areas and the higher
terrain, with amounts approaching 1 inch in the interior
lowlands.

The period of heaviest rainfall looks to occur during
the day on Sunday as PWAT values remain above 1 inch and IVT
values peak in the 500-750 kg/m/s range along the Oregon Coast.
Rainfall Sunday afternoon will also be aided by forcing from a
shortwave trough embedded in southwest flow aloft, along with
the next associated surface frontal boundary. Model QPF during
the day on Sunday depicts an additional 1-2 inches of rain for
the coast and higher terrain, with another 0.75-1.00" for the
interior valleys through Sunday evening. Sunday night will bring
a relative lull in precipitation between systems as transient
upper level ridging passes overhead.

The last in the series of frontal systems will then bring one
more shot of moderate to heavy rain to the area on Monday, this
time focused more along coastal areas. Those coastal areas
could see another 1-2 inches of rain through Monday night, with
an additional 0.50-1" looking more likely for area east of the
Coast Range. The period of heavier precipitation will come to an
end as this upper level trough crosses the region Monday night.
Refer to the Hydrology section below for details regarding
potential flood impacts from this event.

Wind will be the other main forecast concern over the next few
days as the series of seasonably strong frontal systems crosses
the region. The first round of wind is this afternoon into
tonight as the cold front continues moving onshore. Generally
expect winds with this front to gust to 40-50 mph along the
coast. It would not be out of the question to see a stray gust
or two to 60 mph this afternoon on beaches and headlands, but do
not expect these conditions to be widespread enough to warrant
any wind headlines for the coast today. Gusty south winds will
also spread inland to the Willamette Valley this evening.
Expect winds generally in the 25-35 mph range with a few gusts
as high as 40 mph this afternoon and early evening. Sunday`s
system looks to bring similar magnitude winds, with another
round of 40-50 mph along the coast and 25-35 mph winds in the
inland valleys.

Monday`s system looks to bring perhaps the strongest winds of
the event as models show relatively good agreement in a strong
surface low bottoming out around 980 mb as it passes offshore
during the day on Monday while tracking towards Vancouver
Island. NBM probability for 60 mph winds increases to
approximately 50-60 percent along the coast Monday
afternoon/evening. Do not quite have the confidence for a High
Wind Watch on the coast at this time, but that may be a
consideration in future forecast packages. Would expect the
strongest winds to mostly be confined to beaches and headlands,
with gusts more likely to be in the 40-50 mph range for inland
coastal communities. Similarly, Monday`s system will present the
best chance for advisory level winds in the inland valleys as
NBM probs for 45 mph gusts increase to 30-50% from Portland to
Eugene during the day on Monday, peaking near the Salem area.
Will need to pay close attention to how models evolve with
respect to the track of the surface low as a track closer to the
coast will increase the potential for stronger winds across the
area. Will also need to consider the impacts from saturated
soils as that could contribute to the potential for downed
weakened or dead trees over time. /CB/HEC

.LONG TERM...Tuesday through Friday...Showers will be winding
down across the area on Tuesday in the wake of the atmospheric
river as high pressure begins to build in behind the departing
trough. Could see some minor snow accumulations return to the
Cascade passes Monday night through early Tuesday as the passing
trough drops snow levels down to around 4000 feet. Beyond Tuesday,
WPC ensemble clusters indicate a 50/50 chance between a weak
weather system bringing another quick shot of rain on Thursday
or a ridgier pattern developing over the Pacific Northwest and
western CONUS through much of next week, promoting a warmer and
drier pattern across the region. This is reflected in the individual
ensemble members, as well, though even if rain does occur
Thursday, ensemble guidance is in good agreement of low
accumulation amounts. The NBM mean probabilities for for high
temperatures to surpass 60 degrees in the Willamette Valley
during the middle to latter part of next week has lowered
somewhat to around 45-65%. /CB/HEC

&&

.AVIATION...Radar, satellite, and surface observations as of 2330z
Sat depict IFR/MVFR CIGs along the coast and MVFR/low-end VFR CIGs
across the Willamette Valley as a cold front pushes through the
area. CIGs are forecast to fall predominately to MVFR as the front
moves through and brings rain. Guidance suggests a 20-40% chance
that CIGs in the Valley fall to IFR or lower between 06-18z Sun.
Heavy rain at times could briefly reduce visibility to IFR/MVFR
thresholds or lower at any given terminal through tonight

Expect southerly winds with gusts up to 40 kt along the coast and
30 kt across the Willamette Valley. An exception to these
southerly winds would be the Columbia River Gorge and eastern
Portland Metro Area (KPDX/KTTD), where easterly winds may
prevail through this evening. Because winds around 2000 feet are
forecast out of the southwest around 40-50 kt, low level wind
shear (LLWS) was included in the TAFs for all terminals. Expecting
more directional shear towards the Portland Metro and strong
speed shear everywhere else. The threat of LLWS subsides after
03-06z Sun.

PDX AND APPROACHES...Predominately MVFR through the rest of the
TAF period with the frontal passage. Easterly winds around 10-15
kt shifting more southeasterly to southerly with gusts up to 25
kt late tonight into early Sunday morning.        -Alviz

&&

.MARINE...Active weather will continue across the waters this
weekend into early next week. The first front is pushing through
this afternoon, bringing southerly winds with gusts to 40-45 kt
across the waters. Expect gale force wind gusts to continue
through the evening, but after 7-10 PM Saturday winds will ease
slightly for waters north of Cape Falcon as pressure gradients
ease. These areas will see gusts weaken to around 30 kt, while
marine zones south of Cape Falcon will continue to experience
gusts up to 40 kt through Sunday afternoon. Therefore, the current
Gale Warnings remain in effect through Sunday evening. Sunday
night into early Monday morning, winds across all marine zones
briefly weaken under 20 kt before the next robust system arrives.
Seas this weekend through early Monday morning will be around
12-15 feet at 13 seconds, as a combo of wind waves and a westerly
swell.

Monday to Tuesday, a strong low pressure system tracking toward
Vancouver Island is forecast to significantly increase southerly
winds and seas. After mid to late morning Monday, southerly winds
are forecast to increase to 35-45 kt sustained with wind gusts up
to 55 kt. Expect these winds to persist through Monday night and
ease sometime after early Tuesday morning. Seas will be very steep
and choppy. In addition to high wind waves, a dominant
southwesterly swell from this low will also push through the
waters, pushing combined seas above 20 feet beginning early
afternoon Monday and peaking Monday night around 25-30 feet at 15
seconds. Seas are not forecast to fall below 20 feet until late
morning Tuesday. The current Storm Watch remains in effect for all
waters including the Columbia River Bar Monday morning to Tuesday
morning. We`ll also need to monitor the potential for high surf
along the coast during this time. -Alviz

&&

.HYDROLOGY...A fairly long duration atmospheric river event
will be enhanced by several systems crossing the region today
through Monday, leading to multiple periods of moderate to heavy
rain. In all, models have remained fairly consistent in
depicting 72 hour rainfall amounts from this morning through
Tuesday morning of 4-6 inches along the coast and in the
adjacent higher terrain as well as over the Cascades, with 2-3
inches likely in the interior valleys. Amounts of 7+ inches are
not out of the question in orographically favored parts of the
Oregon Coast Range as well as the High Cascades. Rainfall looks
to be fairly evenly distributed each day through Monday, with
1-2 inches of rain along the coast and in the mountains and up
to one inch for the interior lowlands each period. Latest HREF
and NBM guidance indicate the potential for hourly rain rates
near 0.25-0.3 inches at times along the Coast Range and
Cascades, as well.

This will certainly produce rises on area rivers. Expect to see
the largest responses by Sunday evening on some of the flashier
rivers in the Coast Range and Willapa Hills, including the
Grays and Siletz Rivers. Meanwhile, several slower responding
rivers draining from the Coast Range are forecast to reach
action stage Monday into Tuesday. Additionally, a number of
rivers, streams, and creeks in the interior lowlands that drain
from either the Coast Range or the Cascades are now expected to
see rises into at least Action Stage with many locations peaking
just under Minor flood stage except for the Clackamas River near
Estacada which is forecast to exceed Minor flood stage.
Significant snow melt due to high snow levels causing rain to
fall on snow is part of the reason for this increase in river
levels. This increase snow melt along with the hourly rain
rates will also enhance the chance of landslides in the higher
terrain.

The primary impacts in lowlands will likely be related to
ponding of water on roadways and poor drainage in low lying
areas. Do not currently expect any widespread debris flow or
flash flooding concerns as hourly rainfall rates look to max
around around a quarter to perhaps a half inch, and therefore
should remain well below thresholds on area burn scars through
the duration of the event.

A Flood Watch has been issued for the entire forecast area for
northwest Oregon and southwest Washington due to the concerns
mentioned from 4 AM PT Sunday through 4 AM PT Wednesday. Continue
to monitor the forecast closely as relatively minor changes in
forecast rainfall amounts could have significant implications on
potential for potential river and areal flood concerns in the
coming days. -CB/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Gale Warning until 7 PM PST Sunday for PZZ210-251>253-272-273.

     Small Craft Advisory from 7 PM Sunday to 10 AM PST Monday for
     PZZ210-251>253-272-273.

     Storm Watch from Monday morning through late Monday night for
     PZZ210-251>253-271>273.

     Gale Warning until 10 PM PST this evening for PZZ271.

     Small Craft Advisory from 10 PM this evening to 10 AM PST Monday
     for PZZ271.

&&
&&

$$

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