Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 200401
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
859 PM PDT Sat Aug 19 2017

.SYNOPSIS...Weak onshore flow continues through Sunday, particularly
along the Columbia River and the north part of our forecast area. One
last very weak upper disturbance will pass through Sunday afternoon
and night, and maintain the onshore flow before an upper ridge builds
in on Monday and continues Tuesday for warmer temperatures. Low
clouds will mainly be along the south Washington and north Oregon
coast Monday morning and locally inland along the Columbia River. The
upper ridge will reduce the onshore flow for Tuesday. A significant
upper trough will approach Wednesday with increased onshore flow and
a bit of cooling, then some chance of showers Wednesday night and
Thursday. Another upper ridge starts to build by the weekend for
drying and warming.
&&

.SHORT TERM...Tonight through Tuesday...The evening models have come
in without any surprises. Still tracking a very weak short wave
passage Sunday afternoon/early evening, which will keep the modest
onshore flow going through Sunday night. By Monday morning, the
Pacific ridge axis noses northeast to NW Oregon/SW Washington
coastline. Surface winds remain generally onshore, but above 925 mb
winds turning north/northeast by early morning. Current forecast
grids call for shallow stratus SW Washington and along the lower
Columbia River and appear right on track. Could see scattered areas
of thin stratus Cascade foothills along the northern Willamette
Valley, but nothing too substantial. High confidence continues that
the path of total eclipse east of the the coast will be clear. Flow
also turns offshore along central Coast Monday morning, so middle-
range confidence of partly-to-mostly clear skies there. The next two
afternoons should bring plenty of sunshine again, with slightly
above normal temperatures. The remainder of the forecast discussion
is unchanged. DRB

The modest upper ridge will continue over the Pacific Northwest on
Tuesday. The models show some morning low clouds along the coast
Tuesday morning but that coverage inland will be sparse at best.
Temps will again approach 90 inland on Tuesday.

A weak low develops over northern California early in the week and
there is a slight chance of a thunderstorm getting close to
Willamette Pass late Tuesday, though they mainly may end up being in
central Oregon. Tolleson

.LONG TERM...Tuesday night through Saturday...A decent late summer
system will approach Wednesday with increasing southwest flow aloft,
possibly increasing the onshore flow some with a bit of cooling.
There is again a slight chance of thunder near Willamette Pass late
Wednesday but the most likely scenario is that most will stay south
and east of our area. The approaching system moves through Wednesday
night and Thursday with plenty of clouds and some chance of showers.
Some lingering onshore flow will give way to more sunshine on Friday
as conditions begin to improve in the wake of the Thursday system.
Saturday is looking sunny and mild with perhaps a little fog or low
clouds at the coast. Tolleson
&&

.AVIATION...Delayed onset of stratus at KAST as waters remain
mostly clear at this time with no indication of coastal stratus
development yet. Otherwise, forecast seems on track with stratus
possibly extending as far inland as KPDX before quickly mixing
out in the morning. Gusty winds at several TAF sites this evening
will taper off in the next few hours.

KPDX AND APPROACHES...VFR conditions tonight with breezing
conditions this evening tapering off by 05Z. Stratus expected to
reach the terminal for a few hours in the morning before clear
skies arrive for the remainder of the day. /Bentley

&&

.MARINE...A persistent weather pattern will result in little
change in the marine weather the next several days. High pressure
holds over the NE Pacific while a thermal trough is along the
south Oregon coast. This supports north winds across the south
Washington and north Oregon waters. The thermal trough
strengthens each afternoon such that the north winds will
increase and become gusty each afternoon. The winds south of
Cascade Head will have frequent gusts to around 25 kt which
supports the current small craft advisory for winds.

The seas will be locally generated from these winds and generally
remain 4 to 6 ft with periods at 9 to 10 seconds. The seas will
be choppier in the southern waters for the afternoons with
dominant periods possibly around 8 seconds. ~TJ/Bentley

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 11 PM 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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