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fxus66 kpqr 172148 

Area forecast discussion
National Weather Service Portland or
241 PM PDT Tue Sep 17 2019

Synopsis...a cool and unsettled pattern will bring a mix of dry and
wet days through the weekend. After that, some long range models
suggest a drier pattern may return early next week.


Short term...tonight through Friday...a rather strong upper trough
and surface front are affecting the area this afternoon. At 20z the
surface front was just west of the Washington/or coast, with breezy
south/southwest winds mixing down to the surface through most of the
Willamette Valley. This system will continue to move eastward this
evening, with the upper trough moving directly over the County Warning Area
Wednesday. This will bring a mix of sun and clouds and sufficient
instability for scattered-to-numerous showers and isolated
thunderstorms. Model and ensemble forecasts of cape are rather
substantial by pacnw standards Wednesday afternoon, with ensemble
spread from 400-1000 j/kg and largest over the central and south
Willamette Valley. Shear under the upper low is minimal, but cells
may still be vigorous and capable of brief heavy rain, small hail,
and gusty winds. Flow becomes drier and northerly for Thursday as
the upper trough moves east, but the weak ridge nosing into the area
remains cool and somewhat cloudy. Another trough overshooting the
ridge provides a small chance of showers again on Friday,
particularly over the mountains, and then drying for Saturday. Bright

Long term...Friday night through Monday...models are in consensus
through the majority of the long term, but showing some divergence
after Monday. The GFS and ecwmf show a ridge building over the area
through Saturday and should provide a brief dry period for the
region. The next major system to impact the area will be on Sunday.
Models are showing that an upper level trough along with its
associated cold front will start moving across the area. This will
bring an increase in precipitation chances through Monday, as well
as bring temperatures into the mid to upper 60s along the coast and
upper 60s to lower 70s inland.

As Monday night into Tuesday approaches the models show some
divergence. The ecwmf has a weak ridge getting pushed back as a
stronger alaskan upper level trough, while the GFS has the ridge
being much stronger. This results in the ecwmf bringing a chance of
precipitation back to the area early next week, while the GFS keeps
the area dry. This time frame is well beyond the current extended
forecast period but thought it was Worth mentioning. /42

Aviation...mix of lower VFR and MVFR conditions through the
evening as a front continue to move across the forecast area.
Rain and showers will continue, with temporary reductions to MVFR
vsbys possible in heavier showers. Meanwhile, strong south
surface winds continue this afternoon ahead of the front. Higher
terrain (coastal mountains and cascades) will remain obscured in
clouds and rain through much of the period. Gusty winds will
ease this evening, but expect widespread MVFR overnight with
local IFR especially for the coastal terminals.

Kpdx and approaches...VFR this afternoon, but gusty south winds
continue ahead of the front. Another round of steady rain
arriving 22-23z will bring potential MVFR conditions. Behind this
line, transition to showers will bring mix of MVFR/VFR conditions
through the overnight period.Cullen


Marine...gale force winds have ended across the coastal waters
this afternoon, so have allowed the Gale Warning to expire as
planned at 2 PM. Gusts to 25 kt will still be frequent this
afternoon, before becoming only occasional this evening.
Meanwhile, seas will range around 9 to 11 feet through the
evening. While the wind wave/fresh swell component will gradually
subside, dominant periods will remain rather steep (around 9
seconds). As a result, issued a Small Craft Advisory for all
zones through 11 PM to cover both of these hazards. It's possible
that the northern zones may be able to be canceled early, but it
might need to be extended longer in the southern zones.

The surface low slides south to the South Washington waters this
evening and to the north and central Oregon waters by Wednesday
morning. Weak high pressure rebuilds over the region, maintaining
north to northwest winds around 15 kt for much of the remainder
of the week. Seas remain in the 8 to 10 ft range Wednesday, but
then subside to around 5 to 6 feet as high pressure settles over
the waters. Cullen


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory until 11 PM PDT this evening for coastal
waters from Cape Shoalwater Washington to Florence or out 60 nm.



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