Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 250336
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OREGON
833 PM PDT Sat Sep 24 2016
.SYNOPSIS...A strong early autumn upper ridge will be over the
northeast Pacific and the Pacific northwest tonight and Sunday,
slowly moving eastward early next week, producing mild and dry
weather over southwest Washington and northwest Oregon Sunday and
Monday. A weak front will brush the forecast area Tuesday for more
clouds, onshore flow, and spotty light precipitation mainly near the
coast. The area will be in between systems during the mid week
period. The next low is expected to affect the area later in the week
and on next weekend.
.SHORT TERM...(Tonight through Tuesday)...No changes. Previous
discussion follows. A strong upper ridge will continue to build into
the northeast Pacific and the Pacific Northwest tonight and Sunday,
bringing cool nights but mild, dry days with it. The drying air mass
will allow temps to cool at night into the 40s in many lower
elevation areas, but the warming aloft from the upper ridge should
lead to temps well above normal Sunday, probably near or above 80 in
the valleys. Nevertheless, the lengthening nights in combination
with the damp ground left over from the abundant rain from last
weekend should lead to some valley fog later tonight and Sunday
Some clouds may brush the northwest corner of our forecast area
tonight as a warm front passes by north of the area, but then the
upper ridging kicks in for real and that will bring sunny skies to
the area Sunday after the local morning fog.
Look for a repeat of Sunday`s weather on Monday. There could still be
a little morning valley fog. Light offshore flow that develops Sunday
will increase a bit Sunday night and Monday, with gradients through
the Gorge around 4 mb early Monday morning. Thus we could see a touch
of east wind Monday morning.
After that, things change as a weak system approaches the coast
Monday night and onshore early Tuesday. This will cause clouds to
increase along the coast Monday night and Tuesday with a little
drizzle or light rain, and for clouds to spread inland late Monday
night and especially Tuesday morning. Could see some patchy drizzle
inland around the Columbia River Tuesday morning. The onshore flow
should drop temperatures back to near or a bit below normal on
.LONG TERM...(Tuesday night through Saturday)...Upper-level trough
starts to dig southward out of the Gulf of Alaska midweek. Looks to
be a cooler system which will start bringing in cooler air aloft
midweek. This will translate as a gradual cooling trend with dry
and partly cloudy to mostly sunny weather Wednesday and Thursday.
Will start to see increasing clouds Thursday afternoon, while the
Front hangs offshore until Friday. Much uncertainty with the details
of this late week system, but it does look like troughing will hang
over the area into next weekend for cooler than normal temperatures
and a continued chance for showers into at least Saturday. Lower
freezing levels with this system may even bring some snow to the
.AVIATION...High pres over the region will strengthen through
Sunday, while thermal low pres builds on the south Oregon coast.
This pattern will maintain dry air mass, with light north to
northeast winds. Shallow inversions later tonight will allow
pockets of fog to form late tonight, mainly over the interior. Any
low clouds or fog that does form will burn off quickly Sun am.
KPDX AND APPROACHES...VFR over the region tonight and Sunday with
light winds becoming east to northeast later Sun am. Will see
shallow patchy fog between 10z and 15z, mainly to west/northwest
of PDX ops area. fcstr...rockey.
.MARINE...High pres and weak pres gradients over the waters will
continue to bring winds less than 15 kt tonight. Winds will become
northerly early Sun as high pres strengthens over the waters.
Thermal low pres looks to build north along the southern Oregon
coast Sun afternoon/evening which should bring SCA gusts to 25 kt
to the southern outer waters. Will go ahead an issue an SCA for
winds with this package. Slightly weaker winds expected Mon as a
weak front moves across the northern waters. High pres rebuilds
over the waters on Tue, with another round of SCA gusts to 30 kt
likely Tue and Wed. Winds look to become southerly by Thu as a
series of front move across the waters late next week.
Seas are currently around 6 ft this evening. Not much change in
overall seas through Mon, though will briefly be steep and choppy
Sun afternoon/evening and again Monday due to gusty north winds.
Seas look to build towards 8 ft by Tue afternoon and with winds
being slightly stronger we could need a SCA for seas at some point.
PZ...Small Craft Advisory for winds for late Sun afternoon through
late Sun night on waters from Cascade Head to Florence.
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This discussion is for Northwest Oregon and Southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area.