Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 140403 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
903 PM PDT Sun Oct 13 2019

Aviation discussion updated.

.SYNOPSIS...Mostly dry weather is expected through Monday. High
pressure will build into the region tonight with areas of fog and
low clouds forming overnight, especially in the valleys. Areas of
fog will linger into mid-morning on Monday, but will clear for a
sunny and seasonable October afternoon. Clouds will increase on
Tuesday as the first in a series of frontal systems approaches the
Pacific Northwest coast. This will mark a shift toward a much more
active and wet weather pattern for the middle to latter part of the
week.

&&

.SHORT TERM...Tonight through Wednesday...The upper level trough that
moved through the region last night into this morning will move east
of the area tonight. High pressure aloft and at the surface will
build across the region tonight and Monday. Time-height cross
sections show a fairly moist boundary layer throughout the
Willamette Valley that persists through about 18z Monday. With the
low level moisture and light winds, expect to see a mix of fog and
low stratus in the valleys late tonight into early Monday morning.
The low clouds and fog should clear by midday, giving way to a
mostly sunny afternoon on Monday. High temperatures on Monday will
be 3 or 4 degrees warmer on Monday with temperatures at the coast
near 60 and in the lower to mid 60s inland.

The ridge of high pressure will transit the area Monday with the
ridge axis over the northern Rockies on Tuesday. The first in a
series of storms will approach the region late Tuesday. NWP models
have slowed the progression of this front with the front moving into
the coastal region Tuesday night into early Wednesday.Another
slightly stronger front will follow on it`s heels later Wednesday.
/tw

.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 Rosberg.
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...CIGs breaking up and clearing through about 10Z Monday,
then expect MVFR stratus formation inland. Developing light offshore
wind should keep the central coast around ONP clear and VFR next 24
hours. May see IFR "bog fog" develop at KAST with wind direction off
the water at low tide around 14Z Monday. Expect conditions across
the board to lift to VFR and clear between 18Z and 20Z Monday.

KPDX AND APPROACHES...VFR conditions expected through 12Z Monday
with clearing skies. After about 12Z, MVFR conditions appear likely
to develop with a low stratus layer. VFR conditions then expected to
return after 18Z to 20Z Monday and continue through 06Z Tuesday.
Bowen

&&

.MARINE...North to northwest post-frontal winds gusting to 25 kt
continue well away from shore, generally more than 15 nm from the
coast. In addition, northwest swell around 10 ft has moved closer to
shore than anticipated and isn`t subsiding quite as quickly as
forecast. For these reasons, have extended the Small Craft Advisory
in time to 11 PM PDT Sunday as well as in space to include the
nearshore waters in addition to the offshore waters. Still expect
winds and seas to decrease later tonight below 25 kt and 10 ft,
respectively. The remainder of the previous discussion follows. Bowen

The weather pattern becomes much more active beginning Tuesday, and
continuing into next weekend. Beginning Tuesday night and continuing
into Saturday expect winds gusting to 20 to 30 kt as a series of
front move east across the waters. At this point, the Wednesday
system appears to be the strongest, and some gale force gusts with
this system may not be out of the question. Seas are likely to build
above 10 ft by Tuesday evening, and expected to build as high as 15
to 20 ft from late Wednesday into Friday, which will be the biggest
seas since spring.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for coastal
     waters from Cape Shoalwater WA to Florence OR out 60 NM.


&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.


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