Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland Oregon
302 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)...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
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...conditions across the forecast area are currently VFR.
Offshore flow along the coast tonight should keep conditions VFR.
Gusty northerly winds possible at konp Sun afternoon/evening. The
interior will remain VFR through late tonight. Expect fog or low
stratus to develop later tonight across portions of the interior.
Khio, ksle and keug could see periods of IFR/LIFR cigs and vsbys
early Sun morning. East winds near The Gorge tonight will likely
keep low stratus at Bay near kttd and kpdx.
Kpdx and approaches...predominately VFR the next 24 hours. Could
see some shallow ground fog early Sun morning, but east winds near
The Gorge tonight should prevent it from becoming widespread. /64
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 Small Craft Advisory gusts to 25 kt
to the southern outer waters. Will go ahead an issue an Small Craft Advisory 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 Small Craft Advisory 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 7 ft this afternoon. Expect seas near 5
to 7 ft through Mon. Seas will briefly become steep and choppy Sun
afternoon/evening due to gusty north winds, but should remain
below advisory criteria. Seas look to build towards 8 ft by Tue
afternoon and with winds being slightly stronger we could need a
Small Craft Advisory for seas at some point. Seas look to fall below 7 ft late next
Pz...Small Craft Advisory for winds from 3 PM Sunday to 3 am PDT
Monday for waters from Cascade Head to Florence or from 10
to 60 nm.
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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.