Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 182104
AFDPQR

Area Forecast Discussion
Weather Service Portland OR
204 PM PDT Tue Jun 18 2019

.SYNOPSIS...The pattern of areas of morning clouds and some
afternoon sun continues through Wednesday, with seasonable
temperatures. Thursday brings the coolest day of the week along with
a chance for showers as an upper trough of low pressure moves across
the Pacific Northwest. Dry weather and seasonable temperatures
return Friday and Saturday.
&&

.SHORT TERM...Tonight through Friday...Upper heights will continue
to gradually lower tonight and Wednesday as another weak short wave
moves through in the northwest flow aloft. This will continue the
pattern of late night and morning clouds along the coast and in the
northern interior. Daytime temperatures will cool to a bit below
normal as 850 mb temperatures drop another 5 degrees Celsius.

Wednesday night through Thursday night a pair of more substantial
shortwaves carves out an upper trough of low pressure over the
Pacific Northwest. Moisture deepens some with this system, although
models still generally confined it to below 10K feet at its peak
Thursday morning. The moist layer is marginally unstable, so given
the dynamics associated with the shortwaves expect to see some
showers with this system. While most of the forecast area will see
some chance for showers, the best chances will be over the west
facing slopes of the Cascades and Coast Range where orographic flow
will enhance lift. Temperatures will be at their coolest of the
week, with snow levels likely dropping down to the highers passes
for the day before the summer solstice. Any accumulations would be
likely a dusting at best, and would melt quickly during the day due
to some of the strongest solar energy of the year.

Drier weather returns Friday as the upper trough moves east and
ridging builds in from the west. Surface flow to remain onshore, but
becomes more northerly with the surface ridge extending inland into
Washington. This should result in a return to a pattern of morning
clouds and afternoon clearing for the interior, with daytime
temperatures returning to closer to normal after a cool morning.

.LONG TERM...Friday night through Tuesday...The beginning of summer
will not seem like it as a cool and somewhat unsettled pattern
dominates the forecast area. A weak 500 mb ridge is forecast to be
over the area Sat. However, onshore low-level flow will maintain the
pattern of late night/morning low clouds and afternoon clearing. Max
temps Sat will be close to normal. The long-wave pattern begins to
show signs of change Sat night and Sun. A fairly deep 500 mb low is
forecast to be near Haida Gwaii 12Z Sun. Expect a deeper marine
layer Sat night and Sun, with the potential for some light precip in
SW Washington and also the north Oregon coast Sun morning.

By Mon the large upper level trough will be over the NE Pac. The 12Z
operational GFS shows the upper low along 46N 130W at 00Z Tue, while
the 12Z ECMWF is more to the west. The ECMWF ensemble mean suggests
higher-than-average confidence with the upper low out near 135W. The
GFS ensembles show decent continuity, but the mean 500 mb low
position appears to be closer to 130W, similar to the 12Z
operational run. All in all, the latter half of the extended period
will feature below normal daytime temperatures. In fact, the CPC 6-
10 day temp/precip progs indicate well-above average probability of
below normal temps. CPC also suggests above-average confidence for
above normal precip, albeit at a slightly lower confidence level
than temps. The WPC forecast valid Mon and Tue favors a GEFS/ ECMWF
ensemble mean. The deep upper trough eventually swings into Western
Washington and NW Oregon Tue night and Wed. Looking beyond day 7,
the GFS and ECMWF continue the unsettled pattern the latter half of
next week. Weishaar

&&

.AVIATION...Marine layer gradually eroding early this afternoon.
Low-end VFR cigs along the south Washington and north Oregon
coast with generally SCT or fewer clouds over the SW Washington
interior and NW Oregon. Another disturbance is forecast to move
across NW Washington late tonight, which may tend to disturb the
marine layer enough to limit MVFR or lower conditions, even along
the coast. Still expect MVFR to develop along the south
Washington coast to near KTMK this evening. Coastal areas south
of KTMK may hold on to VFR much of the night, but cannot rule out
local IFR conditions after 06Z Wed. MVFR cigs forecast to develop
in the SW Washington interior overnight and extend up the
Columbia River to KPDX around sunrise.

KPDX AND APPROACHES...VFR conditions to prevail through at least
12Z Wed. Another upper level disturbance moves across NW
Washington late tonight, which may act like a dry cold front.
Still, guidance does suggest the potential for MVFR cigs around
12Z Wed. Weishaar

&&

.MARINE...Surface high pressure will reside over the NE Pacific
through the week, while thermal low pressure remains over the
northern California and southern Oregon coast. This will result
in persistent northerly winds. The winds will be the strongest
this afternoon through late evening, with gusts to 25 kt expected
over PZZ255/PZZ275. Wind speeds will be lighter from Wed through
Fri as an upper level trough moves in and weakens the NE Pacific
surface high. Gusts to 20 kt are expected during the afternoon
and evening hours each day, but do not expect that additional
advisories will be required. Will need to watch the area south of
Heceta Head late Wed afternoon for possible 25 kt gusts. Wind
speeds drop off even more this weekend and early next week as an
upper level low settles over the NE Pac.

Seas mostly 4 to 6 ft for the next few days, although areas of
PZZ255 and PZZ275 likely to see brief periods of 6-8 ft at times
due to contributions from fresh swell. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until midnight PDT tonight 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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