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fxus66 kpqr 141802 

Area forecast discussion
National Weather Service Portland or
1102 am PDT Mon Oct 14 2019

Updated aviation section

Synopsis...high pressure will lead to dry and seasonable weather
today and most of Tuesday. Morning low clouds and fog will give way
to afternoon sunshine today, with temperatures near seasonal norms.
Offshore flow and increasing high clouds will likely lead to less fog
tonight and Tuesday morning, with a mostly cloudy but mild day on tap
for Tuesday. A pair of approaching Pacific frontal systems will
spread rain onshore Tuesday night and Wednesday, and rain may be
locally heavy along the coast and in the higher terrain. This front
will mark a shift toward a much more active wet and blustery weather
pattern which will likely last into the upcoming weekend.


Short through Wednesday...mainly benign weather is
expected today, though there are some areas of fog that have
developed overnight. Morning fog and low clouds will gradually give
way to increasing sunshine as today progresses, with seasonable
temperatures. High pressure will center itself east of the Cascades
tonight, leading to modest offshore flow through Tuesday. This, along
with increasing high clouds associated with an incoming frontal
system, should lead to less fog tonight and Tuesday
least for the northern half of the forecast area. Despite 850 mb
temps warming by 2-3 deg c, thickening high clouds Tuesday should
keep high temps similar to Monday.

The increasing/thickening high clouds will be a sign of changes ahead
as a pair of Pacific frontal system approaches the pac northwest coast
Tuesday. Models and their ensembles suggest the first front will slow
down while approaching the coast, as a wave of low pressure develops
along the front and lifts north-NE into British Columbia. The stronger of
the two frontal systems appears to be the second one, which will be
moving eastward much faster than the first front and should arrive
Wednesday. The main reason for the faster movement of the second
system is the 140 kt+ jet developing today near the southern portion
of the Kamchatka peninsula of Russia and the western Aleutians. So,
expect rain to develop along the coast Tuesday night, then spread
onshore and become heavier going into the day on Wednesday.

This second system will also incorporate moisture and energy from
once-Typhoon Hagibis which recently made landfall near Tokyo, Japan.
As a result, gefs ensembles show a high level of confidence of a
moderate atmospheric river making landfall along the Washington/northern or
coast Wednesday. This will elevate the risk of heavy rainfall across
the forecast area, especially across SW Washington and the
coast/higher terrain of northwest Oregon where 1 to 3 inches of rain are
possible by Thursday morning. Inland valleys will likely receive 0.50
to 1.00 inch of rain during the same time period, with locally higher
amounts in SW Washington. With rivers running low due to it being the
early portion of our rainy season, flooding is not expected, though
there may be some localized short-duration issues due to heavy rain
rates, particularly in urban areas with poor drainage.

Another aspect of this system to keep an eye on will be winds along
the coast, as the 06z NAM shows a 50-60 kt southerly coastal jet
descending to 950 mb Wednesday morning. However, gradients appear to
be too easterly for the strongest gusts to move much inland from the
beaches and headlands. For now, it looks like gusts will top out at
40 mph for most coastal areas Wednesday, with exposed terrain and
beaches perhaps seeing a few gusts up to 45-50 mph just ahead of
wednesday's cold front. Weagle

Long term...Wednesday night through Sunday...models and their
ensembles are in good agreement a series of shortwave troughs will
slide east-southeastward across the Pacific northwest during the
second half of the work week. This will result in a multi-day
stretch of wet weather. While no one day looks unusually wet,
rainfall amounts will likely add up over time. Based on the gefs and
ec, it appears an additional 0.50-2.00" of rain on top of Tuesday
night/wednesday's rain will be possible in the Willamette Valley
Wednesday night through Saturday with an additional 1-3" along the
coast and an additional 2-5" rain in the Coast Range and Cascades.
Given these rainfall amounts will be spread out over several days,
mainstem river flooding appears unlikely at this point...even at our
most flood prone rivers including the Grays River at Rosburg.
Nonetheless, rivers will certainly be on the rise and the weather
will be reminiscent of many past November days.

It should be noted that subtle differences exist between models and
various ensemble members in timing and amplitude of upper level
shortwave troughs so there is still some uncertainty on when showers
will be more or less numerous across the region. Nonetheless, there
is at least some indication Thursday afternoon or evening could see
a spike in rain coverage as an occluding front drops southeastward
into the region. In addition, it appears the region will be on the
edge of the 500mb cold pool Wednesday night and again on Thursday
night or Friday so there will be a risk for a thunderstorm or two
over the northern waters, and perhaps even inland, but there remains
enough uncertainty to leave it at that for now.

Pressure gradients will also be favorable for breezy to windy
conditions along the coast late Wednesday and Thursday, but at this
point models suggest wind fields should be weak enough to
prevent any high wind issues along the coast.

Finally, wet weather may very well continue into Sunday, but models
and their ensembles suggest it's less likely than Saturday so pops
were maintained in the chance to low end likely range per nbm
guidance for now. It should be noted that the some of the recent
operational ec and GFS runs do suggest an atmospheric river riding
up and over the shortwave ridge building across the eastern Pacific
could take aim at the Pacific northwest late Sunday and beyond so
that will be Worth monitoring, particularly given the rain
anticipated to fall this week. /Neuman


Aviation...areas of fog through the Willamette Valley and Columbia
River gorge are beginning to dissipate and will continue to do so
through 20z on Monday. At that time, most areas will return to VFR
or MVFR conditions, with potentially patchy fog remaining in the
southern Willamette. North-northeasterly flow will be dominate
through 04z Tuesday, then winds will shift to an easterly direction.
The main challenge for this package is the regeneration of fog and
low stratus overnight after 08z Tuesday. Areas of specific concern
are keug and khio, where ceilings and visibility may drop to IFR
after 12z Tuesday. It is possible for these impacts to be more
widespread but significant dry air aloft should keep areas fog free.

Kpdx and approaches...fog dissipating to VFR conditions by 20z
Monday. Winds remain generally northerly shifting to an easterly
flow after 12z Tuesday. MVFR ceilings and reduced visibility
possible after 12z Tuesday. -Muessle


Marine...high pressure to reside over the waters through Mon
evening, which will result in wind speeds 15 kt or less. High
pres weakens Mon night into Tue as the first in a series of
frontal systems approaches the waters. Latest model guidance
suggests boundary layer wind speeds reach Small Craft Advisory
levels over the outer waters between 12z and 18z Tue. Solid Small
Craft Advisory speeds develop Tue afternoon. The 00z NAM shows
975 mb wind speeds of 35-40 kt across pzz270 Tue afternoon. The
975mb level is a good proxy for peak wind gusts, provided some of
the wind aloft is allowed to mix down to the near-surface layers.

In any event, gales are a possibility Tue afternoon through Wed,
otherwise Small Craft Advisory level wind speeds are likely
through much of the upcoming week. The longer range indicates a
quieter pattern developing next weekend.

Seas took awhile to fall below 10 ft, but as of 09z wave heights
were in the 7-9 ft range. Spectral bulletin guidance, Hanson
plots and enp/wam graphical guidance all in good agreement
indicating 10 ft seas developing over the outer portions of
pzz270 Tue afternoon. Seas continue to build through mid-week,
peaking around 20 ft Thu. This will be the highest sea state
since the Spring. Models show wave heights gradually subsiding
late in the week and into next weekend. Weishaar


Pqr watches/warnings/advisories...



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