333
FXUS66 KPQR 150559
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
959 PM PST Thu Nov 14 2024

Updated aviation and marine discussions

.SYNOPSIS...Post-frontal showers will continue through Thursday
before decreasing in coverage Thursday night into Friday. Some
clearing Friday night will favor chilly overnight lows with near
freezing to below freezing temperatures likely, especially in
rural areas. Areas of frost Saturday morning, then back to wet
and breezy conditions late Saturday through Sunday as a Pacific
frontal system moves inland. Post-frontal showers Sunday night
into Monday will end by Tuesday as offshore flow develops,
bringing several days of dry weather with breezy east winds
Tuesday through next Friday.

&&

.SHORT TERM...Now through Friday Night...On-off showers continue in
the unsettled post-frontal regime. While a stray thunderstorm or two
may remain possible through Thursday evening (particularly at the
coast), these will be much weaker and more isolated than Wednesday.
The coast sees around a 10-20% chance of thunderstorms during this
time. Snow levels are currently around 3500-4000 ft, but snow at the
passes should remain fairly light; under 1 inch through Friday
morning. Light insubstantial showers continue to taper off going into
Friday, likely drying out Friday evening.

Going into Friday night, upper level northerly flow and cloud breaks
could lead to developing patchy fog and frost. Temperatures at the
end of Friday night show around a 60-80% chance of temperatures at or
below 32 degrees in the Willamette Valley and much of the Columbia
Lowlands, with the exception of heavily urban areas which will stay a
few degrees warmer. Frost will be possible late Friday night and
early Saturday morning, with any wet surfaces possibly becoming slick
during that time. /JLiu

.LONG TERM...Saturday through next Friday...While conditions will
likely start off dry on Saturday with areas of morning frost,
conditions will change fairly quickly as cloud cover increases ahead
of an incoming swath of stratiform rain associated with a Pacific
frontal system. Rain associated with a warm front will begin first,
impacting the coast by late Saturday morning and inland areas by the
late afternoon. Snow levels look to rapidly rise to 6000-7000 feet
Saturday evening into Saturday night as the warm sector behind the
warm front spreads farther inland.

Shortly after the warm frontal passage, a cold front will follow.
Models seem to agree well on the timing of this cold front, pushing
eastward over western WA/OR on Sunday. This will bring yet another
round of stratiform precipitation on Sunday, albeit heavier than the
first round. A Winter Storm Watch has been issued for all Cascades,
as the 24 hr period from 10am Sunday to 10am Monday could see areas
reaching up to 10-15 inches during that period, with 60-70% chance of
seeing over 12 inches.

Post-frontal showers will then continue Sunday night into Monday
along with a 15-20% chance of thunderstorms at the coast. WPC and NBM
QPF do not suggest enough rain will fall for river flooding to occur,
however there is some uncertainty. The wettest ensemble members from
the GEFS/EPS suggest minor river flooding may be possible for a few
coastal rivers, albeit the probability for river flooding is low
(5-15% for minor flooding along the Willapa River near Willapa, the
Naselle River near Naselle, the Nehalem River near Foss, and the
Wilson River near Tillamook). All other rivers have less than a 5%
chance to reach minor flood stage, aside from the Grays River near
Rosburg which will also need to be monitored closely as this river
responds quickly to heavy rain. This system will also bring breezy
south winds, albeit not strong enough for significant impacts to
occur. Will also need to watch for potential minor urban flooding in
low-lying areas that have poor drainage and clogged storm drains.

The weather pattern quickly changes Monday night into Tuesday as
offshore flow develops. As of right now, it looks like there will be
a solid four days in a row or more with dry offshore flow
and breezy east winds, from Tuesday through next Friday. Winds will
be strongest in the Columbia River Gorge, eastern Portland metro and
high Cascades, however exact wind speeds are uncertain at the moment.
-TK/JLiu

&&

.AVIATION...Isolated showers are dwindling but continue as
northwest flow aloft remains. Generally VFR expected tonight into
Friday per CONSShort guidance. But HREF guidance shows about a 50%
chance for MVFR cigs backbuilding into from the Cascades toward
Willamette Valley from about 12Z to 23Z Fri, mainly affecting
KTTD, KPDX, KUAO. While the air mass should be mixy enough to
prevent dense fog, think there will be some spots that could have
some vis reductions such as KHIO area.

PDX APPROACHES...Currently MVFR prevailing in KPDX area but most
guidance show improving conditions next couple of hours (around 08Z).
Then as mentioned above HREF shows about a 50% chance for MVFR
cigs 12 to 23Z Fri. Because forecast confidence is low due to
differences in guidance have opted to leave out MVFR cigs in 06Z
TAF for now.

&&

.MARINE...Have extended Hazardous Seas Warning to Friday morning
as guidance is too low, about 2-4 feet below observations.

Previous discussion follows...Winds have shifted to the NW with
the passage of a cold front earlier today. Wind speeds have also
come down a bit, generally 10-15 kts with gusts up to 20 kts.
Westerly swell at 14 to 17 feet around 13 to 16 seconds continues
this afternoon but is expected to decrease this evening into the
low teens around 12-13 feet at 12-13 seconds. Once this swell
passes the wave state finally calms for the second half of Friday
into Saturday with significant wave heights dipping below 10 feet.
Could see a slight uptick in wave heights late Saturday as a
front moves through, increasing the wind wave component.

Small Craft Advisory for steep seas for all zones tonight into
Friday. A couple of quick disturbances are expected bring
increasing seas back into the low to mid teens and high- end Small
Craft, low-end Gales late Saturday through Sunday. Looking farther
ahead, potential exists for a stronger system to impact the region
sometime during the Tue/Wed timeframe next week. Strength, timing,
and location vary widely among the models at this time. -Batz

&&

.BEACH HAZARDS...Minor tidal overflow flooding is possible along the
south WA/north OR coast around high tide over the next few days as
the Perigean spring tides continue, however the predicted total tide
looks to be right at or just shy of meeting criteria for a Coastal
Flood Advisory. The exception looks to be around high tide Sunday
afternoon when the total tide is forecast to reach 11.6 feet. This
exceeds our 11 foot criteria for a Coastal Flood Advisory, so there
is a good chance a headline will be issued within the next day or two
as confidence increases. Potential impacts include minor flooding and
erosion in the low lying areas near bays, sloughs, highway 101, and
the lower reaches of the coastal rivers. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Storm Watch from late Saturday night through Monday
     afternoon for ORZ126>128.

WA...Winter Storm Watch from late Saturday night through Monday
     afternoon for WAZ211.

PZ...Hazardous Seas Warning until 8 AM PST Friday for PZZ210.

     Small Craft Advisory from 8 AM to 4 PM PST Friday for PZZ210.

     Hazardous Seas Warning until 10 AM PST Friday for PZZ251>253-
     271>273.

     Small Craft Advisory from 10 AM to 4 PM PST Friday for
     PZZ251>253-271>273.
&&

$$

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