Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 221012
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
312 AM PDT Sat Jul 22 2017

.SYNOPSIS...A flat upper ridge will bring warming to southwest
Washington and northwest Oregon Saturday that will continue into
early next week despite a system passing by to our north Sunday and a
weak low to our southwest Sunday through Tuesday. A weak warm front
moving onshore from the northwest will brush the far north coast with
some clouds and possibly some spotty light precipitation today. The
remnants of the cold front will move onshore tonight and may give us
some brief low clouds inland Sunday morning. The low to our
southwest will likely produce some thunderstorms in the Lane County
Cascade forecast zones Sunday through Tuesday before moving eastward.
Increased onshore flow and cooler temps are expected for the second
half of next week.

&&

.SHORT TERM...Today through Monday...High pres anchored over the
interior western U.S. will keep flat ridging over the Pac NW through
the weekend and into early next week. Upper level heights will
fluctuate from day to day, but remain generally high over the region,
with temperatures above average through the period. Light onshore
flow will keep temps at the coast much cooler.

Most of SW WA and NW OR remain cloud free this morning. However, a
low pres system approaching the B.C. coast is bringing a weak warm
front toward the WA/OR coast, and associated clouds are pushing into
our far northern coastal zones. The main cloud cover will remain
confined to the coast today, and there is also potential for some
coastal drizzle or light rain through the morning hours. Otherwise,
expect a mostly sunny, and hot day across the CWA. 850 mb temps are
up 3-4 deg C from yesterday, which should support highs in the upper
80s to low 90s for the interior lowlands. Dew points will also be
increasing into the low 60s due to the weak frontal system, so it
will definitely feel on the muggy side this afternoon.

The low pres system to our north will move onshore tonight into
Sunday, bringing the remnants of a cold front onto the Pac NW coast.
This may deepen the marine layer just enough to assist in bringing
some patchy clouds into the northern Willamette Valley during the
morning, but otherwise expect clouds to again be limited to the coast
to start the day. The trough also drops temps aloft by a couple of
degrees. So expect Sunday to be slightly cooler than today, but highs
should still make it into the mid to upper 80s for the interior
lowlands.

Upper level heights increase again on Mon. If any marine stratus
clouds form overnight Sun into Mon morning, they should remain
limited to the coast. The latest MOS guidance is now suggesting that
Mon will be at least as warm, if not a couple of degrees warmer, than
we see Sat. So the interior lowlands have fcst highs into the low
90s, with a few mid 90s not out of the question.

A low pres system currently apparent on water vapor satellite near
36N/133W will slowly drift toward the northern Calif coast this
weekend. The fcst models indicate that it will stall just offshore
later Sun and remain nearly stationary for the next couple of days.
The southerly flow aloft ahead of this system will bring some
instability and modest mid-level moisture into southern OR, leading
to the potential for thunderstorm activity. The potential is highest
to the south of our CWA, but the threat does appear to extend into
the Lane County Cascades and foothills. The fcst carries a slight
chance for thunder in these zones from Sun afternoon through Mon
night. Pyle

.LONG TERM...Monday night through Friday...Models have started coming
into better agreement with the handling of the upper low spinning off
the California coast early next week. Both the ECMWF and GFS hold the
low offshore on Monday and start lifting it towards central Oregon on
Tuesday which continues the thunder threat through Tuesday. However,
the low is also continuing to track further south each run which is
precluding any thunder threat further north along the Cascades. In
addition, it is worth noting that the beginning stages of the upper
low cutting off can be seen on water vapor just inside 140W, but the
moisture appears quite limited. This lends support for moisture being
a limiting factor and the nature of the storms being high based and
somewhat dry (hence the fire weather concern).

Besides the thunder threat Monday and Tuesday along the central
Oregon Cascades, dry conditions will prevail with temperatures at or
slightly below normal.

The models suggest some degree of troughing along our coast during
the second half of next week though there are some differences
amongst the models. There should at least be some cooling back down
near normal. Tolleson
&&

.AVIATION...Clouds associated with a dissipating frontal system
are spreading down the coast from WA this morning, with MVFR cigs
at KHQM and near-MVFR cigs at KAST. These clouds will probably
have a hard time making it south of KTMK, as the front stalls and
dissipates this morning. Otherwise, VFR and mostly clear skies
should prevail for most of the forecast area through this
evening, aside from some patchy morning fog in some of the more
wind-sheltered valleys.

KPDX AND APPROACHES...VFR conditions through this evening. Winds
will be rather light this morning, then moderate onshore flow
will develop this afternoon and continue well into tonight.
Weagle

&&

.MARINE...Winds and seas will start to increase this afternoon
for what will be a fairly prolonged period of gusty N winds
tonight through at least Monday morning. A weak frontal system is
stalling and dissipating near the mouth of the Columbia this
morning. This will allow high pressure to strengthen over the NE
Pacific, while hot weather over SW Oregon and NW California
strengthen a thermal trough of low pressure over those areas.
This will drive an increase N winds this afternoon, with gusts
25-30 kt expected across our southern waters by sunset and
spreading north into our northern waters overnight tonight. The
increasing N winds will result in steepening wind-driven seas
later this afternoon and into tonight. Winds continue to increase
Sunday, with some models suggesting gale force winds possible in
the southern waters. Gale force northerlies are pretty rare in
our waters, so considering the fact even the stronger models are
only showing marginal gales we opted to go with a Small Craft
Advisory for both the winds and hazardous seas late this
afternoon/evening through early Monday morning. SCA conditions
may very well continue longer than that, with the 00z GFS showing
gusty N-NW winds persisting through Tuesday. Eventually most
models bring an upper trough from the Gulf of Alaska closer to
our waters, which should eventually bring a decrease in
winds/seas middle to late next week.

Although morning ebbs are very strong due to the new moon, there
remains very little swell available to produce rough Columbia
River Bar conditions. As winds increase off the Pac NW waters
later today through tonight, we may need an SCA for Rough Bar
with Sunday morning`s very strong ebb. Will hold off on
highlighting this for now, until we get a better idea what seas
will be at the Columbia River Buoy at ebb time tomorrow morning.
Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 6 AM PDT Monday
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 nm.

     Small Craft Advisory from 4 PM this afternoon to 6 AM PDT
     Monday for Coastal Waters from Cascade Head OR 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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