983
FXUS66 KPQR 230601 CCA
AFDPQR

Area Forecast Discussion National Weather Service Portland OR 958 PM
PST Sat Feb 22 2025

UPDATED ALL SECTIONS

.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...Atmospheric
river has pushed into the area, though rain rates at the moment are
fairly low throughout the area. Expect rainfall to increase
throughout the night; 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. High Wind Watch has been issued for the coast,
Coast Range, and Willapa Hills as a result. Strongest winds mostly
confined to beaches and headlands and upper elevation areas of the
Coast Range and Willapa Hills, 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...The entire 06z TAF period will be dominated by
widespread stratiform rain, moderate to heavy at times with
surface visibilities falling into the 2-4 SM range. In addition to
the rain, gusty south winds will continue over the area with
occasional wind gusts up to 30-40 kt, except up to 45 kt at KONP.
Note the strongest wind gusts will occur after 18z Sunday. Also
expecting strong low-level wind shear at KONP Sunday afternoon
around 2000 ft at 50-55 kt. Lastly, cigs will generally remain in
the high- end LIFR to low-end IFR range at the coast and high-end
IFR to low-end MVFR range inland.

PDX AND APPROACHES...Expect steady rain throughout most the 06z
TAF period with low-end MVFR cigs. Could see high-end IFR cigs
near 1000 ft from 11z-18z Sunday (50-60% chance). Gusty south
winds will continue with occasional gusts as high as 20-30 kt,
strongest after 18z Sunday. -TK

&&

.MARINE...Active weather will continue across the waters through
at least Monday night. 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
Sunday afternoon, except over PZZ271 (the northern outer waters)
where winds have decreased to around 20 kt or less as of 9 PM
Saturday. Aside from this zone, Gale Warnings remain in effect
through Sunday evening to cover the ongoing wind threat. Sunday
night into early Monday morning, winds across all marine zones
briefly weaken under 20 kt. 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. Given the increasing confidence for widespread
storm force wind gusts with this system, the Storm Watch has been
upgraded to a Storm Warning for all marine zones, including the
Columbia River Bar. This warning is in effect from Monday morning
to Tuesday morning. In addition, confidence is high that high
surf advisory criteria will be met with breakers up to 25 to 30 ft
in the surf zone. A High Surf Advisory has been issued for this,
which is discussed in more detail in the beach hazards discussion
below.

&&

.BEACH HAZARDS...There is high confidence for high surf conditions
at the coast from 4 PM Monday to 4 PM Tuesday, which is when a
High Surf Advisory is in effect. This is when large waves and
hazardous surf conditions are expected due to an increasing west-
southwesterly swell, peaking around 25 ft and producing breakers
in the surf zone up to 30 ft. Destructive waves may wash over
beaches, jetties, and other structures unexpectedly. People can be
swept off rocks and jetties and drown while observing high surf.
Minor beach erosion may damage coastal properties and buildings.
Higher than normal water run-up is expected on beaches and low-
lying shoreline.

In addition, cannot rule out minor tidal overflow flooding around
high tide on Tuesday, however confidence is low as the outcome
will be highly dependent on exact river levels and if they are
able to reach approximately 80% of flood flow or higher. This is
because the forecast total tide alone is not high enough to
suggest coastal flooding will occur, however background river
levels must also be considered in addition to the total tide
forecast when determining potential flood impacts. As of right
now, it appears we will be just shy of meeting criteria to issue a
Coastal Flood Advisory, but this could change with future forecast
updates if confidence increases. -TK

&&

.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...High Wind Watch from Monday morning through late Monday night
     for ORZ101>103-106-107.

     High Surf Advisory from 4 PM Monday to 4 PM PST Tuesday for
     ORZ101>103.

WA...High Wind Watch from Monday morning through late Monday night
     for WAZ201-203.

     High Surf Advisory from 4 PM Monday to 4 PM PST Tuesday for
     WAZ201.

PZ...Gale Warning until 7 PM PST Sunday for PZZ210-251>253-272-273.

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

     Storm Warning from 7 AM Monday to 4 AM PST Tuesday for PZZ210-
     251>253-271>273.

     Gale Warning until 10 PM PST this evening for PZZ271.

     Small Craft Advisory until 7 AM PST Monday for PZZ271.

&&

$$

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