Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 251012
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OREGON
245 AM PDT Sun Sep 25 2016
.SYNOPSIS...High pressure will bring a short lived warm spell today
and Monday before a cloudier and cooler weather pattern returns
Tuesday and lingers through at least next weekend. In addition, wet
weather appears increasingly likely to return next weekend.
.SHORT TERM...Today through Wednesday...A strong upper level ridge
will shift over the Pacific Northwest today and Monday, which likely
bring one of our last (if not the last) rounds of summer-like
temperatures to the region this year.
Some mid and high level clouds riding up and over the ridge are
currently moving across our northern zones early this morning, but
should shift northward as shortwave riding builds more solidly into
the region later today. Fog development has been limited thus far,
and given current dewpoint depressions in the south Willamette
Valley and the clouds up north, fog coverage was trimmed accordingly
and where it was left intact, it was shifted towards patchy wording
for this morning.
A thermally induced low pressure trough currently residing over
southwest Oregon will spread northward into the region this afternoon
with 850mb temperatures warming to near 20C by this evening. Given
the lower sun angle this time of year and lack of significant
easterly flow, surface temperatures should not fully realize these
warm temperatures aloft, but should still climb into the low to mid
80s when all is said and done later today. Thermal low pressure will
linger over the region into Monday, which will likely be the warmest
day with temperatures rising into the mid to upper 80s in the
As thermal low pressure shifts east of the Cascades Monday, marine
stratus offshore should push onto our coast during the late
afternoon and evening on Monday before spreading farther inland
A somewhat impressive looking shortwave trough near 150W will weaken
considerably as it moves towards the Pacific Northwest late Monday
night and Tuesday. A dying front associated with this system may
help wring some light drizzle/rain in a few places, particularly
along our northern coastal zones during this time, but any rainfall
amounts appear very light. Nonetheless, this system will help enable
a shortwave trough currently in the Bering Sea to move into the
northeast Pacific mid to late week, which should keep temperatures
near to below average across northwest Oregon and southwest
.LONG TERM...Wednesday night through Sunday...Onshore flow looks to
keep temperatures near to below average during the latter half of
the work week and next weekend. An upper level trough sliding into
the northeast Pacific and Pacific Northwest Friday through Sunday
should bring periods of showers and even cooler temperatures. While
confidence timing embedded shortwave troughs and attendant rounds of
precipitation is low, opted to boost PoPs into the likely category
for a good portion of the forecast area Friday and/or Saturday.
Given the trough will likely be slow to move out of the area, held
PoPs above climatology into Sunday. Snow levels should generally
remain above pass level during this period, but another round of
snow for the volcanoes above 5500-6500 ft appears likely. /Neuman
.AVIATION...VFR conditions under high pres early this morning.
There remains a chance for patchy fog with IFR conditions this
morning, mainly in the central to south Willamette Valley where
skies were clear and winds light, but low dewpoints suggests any fog
is not likely to be widespread or long lasting. Best possibility for
fog will be at KEUG and KSLE between 12z and 17z. Otherwise expect
VFR conditions today and through 10z tonight.
KPDX AND APPROACHES...VFR conditions today and tonight with less
than a 10 percent chance of any fog lowering conditions to MVFR
or IFR category between 12z and 17z.
.MARINE...A trough of low pres along the south Oregon coast this
morning is expected to strengthen today and spread up the Oregon
coastline. This will bring stronger north winds to the waters off
the central Oregon coast late today and into tonight. Peak gusts are
expected to be over the outer waters, reaching 20 to 25 kt. Next
threat of small craft winds comes as northerly winds follow behind a
cold front Tue, and continuing through Wed.
Seas expected to remain relatively low, in the range of 5 to 7 ft,
through Mon night. Seas likely to become steeper and build into the
7 to 10 ft range Tue through Wed as wind waves and fresh swell
building response to the increasing winds.
PZ...Small Craft Advisory for winds from 3 PM this afternoon 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.