Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 191107
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 AM PDT Tue Oct 19 2021


.SYNOPSIS...After a brief break in the wet weather today, expect a
very active weather pattern to bring valley rain and high mountain
snow every 12-24 hours through early next week. A brief burst in wind
will be possible late tonight and Wednesday morning with additional
stronger bouts of wind possible over the weekend and/or early next
week.


&&


.SHORT TERM...Today through Friday...Water vapor satellite imagery
reveals a shortwave ridge over the Pacific Northwest being shunted
eastward as a shortwave trough over the eastern Pacific slides
towards the region. Models are in good agreement this shortwave
trough will take on a negative tilt as it pushes into the Pacific
Northwest tonight. This will spread a band of rain from southwest to
northeast across the area this evening/overnight. The fast moving
nature of this system will limit rainfall totals. However, strong
mid level forcing and modest low level convergence along the front
will likely bring a burst of more intense rain, and perhaps more
notably, some gusty winds. Several high resolution models suggest
wind gusts between 30-45 mph will surface along portions of the
coast and in at least isolated spots in the Willamette Valley around
daybreak as winds aloft mix down with frontal passage and/or with
convective elements embedded along the front.

It should be noted that the operational GFS is an outlier within the
GEFS system, but does bear some resemblance to many members within
the EPS system and a few members in the CMCE system, all of which
suggest a surface low pressure between 995-1003mb forming along the
front off the Oregon coast as it shifts northeastward towards the
region. This doesn`t seem unreasonable given the pattern, but
uncertainty in the magnitude of this embedded wave along the front
does bring some uncertainty in whether or not stronger winds will be
possible, particularly for the coast. The operational GFS`s worst
case scenario depiction would likely only result in marginal to low
end High Wind Warning gusts of ~60 mph along the most exposed
beaches and headlands from approximately Tillamook northward late
tonight into early Wednesday morning. Many of the slightly weaker
low pressure scenarios depicted by the EPS and CMCE members would
likely produce sub-warning wind gusts. As a result, opted to
increase winds along the coast to account for these windier
solutions, but given most ensemble guidance suggests just a breezy
period, will hold off on any wind highlights at this point.

Meanwhile, models are in good agreement a shortwave trough racing
eastward across the Aleutian Islands early this morning will
interact with tropical moisture and result in one of the more
impressive bomb-cyclogenesis events to occur in recent history off
the Pacific Northwest coast Wednesday. Fortunately, the rapidly
deepening low pressure will be far enough removed from OR/WA that
the worst of the wind hazards accompanying it will remain well
offshore Wednesday night into Thursday. In fact, ensemble guidance
continues to support the idea that between the attendant front
weakening as it approaches the region and pressure gradient forces
remaining oriented strongly offshore, winds should remain well below
High Wind criteria along our coastline. Nonetheless, this storm
system will likely bring a solid shot of rain to the region late
Thursday and it will generate a swell that will result in a sneaker
wave threat along our coast Friday. Expect cooler temperatures
Friday with precipitation turning more showery in nature. /Neuman


.LONG TERM...Friday night through Monday...There continues to be
above average agreement in the general weather pattern, which will
feature a strong zonally oriented jet racing eastward across the
Pacific Ocean towards northern California and southern Oregon. This
will result in an extended stretch of particularly active weather
across the Pacific Northwest that will feature below average
temperatures with periods of rain/showers every 12-24 hours. NBM
PoPs support this idea and generally range in the 80-95% range in
each 12 hour period throughout the extended forecast. The first
storm system of the extended forecast period will likely affect the
region Friday night. A front should spread east-southeastward across
the region Friday night and result in a solid shot of rain areawide
with some potential for wind headlines along the coast depending on
how the parent low pressure strengthens. Confidence in details
beyond this time dwindles rapidly, though.

An operational model or two over the past day and a few more of the
00z ensemble members than 24 hours ago suggest a cyclogenesis event
occurring in the vicinity of our coastal waters over the weekend or
early next week. A few of these scenarios would almost certainly
result in high winds along our coast and in the Willamette Valley.
Nonetheless, it still appears to be a rather small percentage (~10%)
of the available ensemble guidance, but bears watching given the
pattern. /Neuman


&&


.AVIATION...12Z TAFs: Generally VFR with high clouds on the
leading edge of approaching frontal system moving over the
region. Conditions favorable enough for radiational fog to in
the interior, but coverage is currently spotty with KKLS, KMMV,
KCVO & K77S reporting IFR fog. May see fog develop at KHIO and
KEUG as well in the next few hours. HREF IFR probabilities show
40-60% chance generally surrounding the Willamette River between
KUAO and KEUG, but go below 10% at 18Z. May also see low stratus
or fog in the KPDX area a couple hours this morning. Will see
rain chances increase this afternoon at the coast, then spread
inland late in the evening. But at this time expect VFR flight
conditions.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...VFR conditions are expected to continue
through early Wednesday. There is a modest chance of fog or low
stratus 12-16Z for IFR conditions at KPDX and KTTD. Will see
rain developing to night but VFR is expected to continue.


&&


.MARINE...A strong front will approach the region later today
into Wednesday. Gale force winds are likely over the outer waters
move to the outer waters around midday then closer to shore
overnight and early Wed morning. Some models showing a strong
wave on the front early Wed morning, but vary on the strength and
timing of this feature. About 25 of 50 ECMWF ensemble members show
gusts 40-48 kts at 12Z Wed for buoy 46050. So feel it is
reasonable for change the current SCA to a gale warning for
PZZ 250 & 255 for Wed morning. Expect periods of enhanced
southerlies to then persist through the end of the week as
another front moves through the waters Thursday which could bring
another round of gales.

Meanwhile, seas will around 7 feet dominated by The next front
will bring an uptick in short period seas late tonight into
Wednesday, peaking around 12-15 ft nearer to shore and near 20
feet beyond 35 NM early Wednesday. Seas settle some later
Wednesday to around 8 to 10 ft as a fresh westerly swell arrives,
but with next gales Thursday seas will probably rise into the m15
to 20 ft range with highest seas offshore.


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT this morning for coastal
     waters from Cape Shoalwater WA to Florence OR
     from 10 to 60 nm.

     Gale Warning from 11 AM this morning to 11 AM PDT Wednesday for
     coastal waters from Cape Shoalwater WA to Florence OR
     from 10 to 60 nm.

     Small Craft Advisory from 8 PM this evening to 2 AM PDT
     Wednesday for coastal waters from Cape Shoalwater WA to
     Florence OR out 10 nm.

     Gale Warning from 2 AM to 11 AM PDT Wednesday for coastal waters
     from Cape Shoalwater WA to Florence OR out 10 nm.

&&


$$


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