Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 241636
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
931 AM PDT Mon Jul 24 2017

.SYNOPSIS...Expect a mix of morning clouds along the coast and lower
Columbia River valley, plenty of afternoon sunshine and high
temperatures near to slightly above average for much of the next
week.


&&


.SHORT TERM...Today through Thursday...Overall expect few
appreciable changes to our weather over the coming days.
Southwesterly to westerly flow aloft and low level northwesterly
flow will produce some morning clouds along the coast and lower
Columbia River valley. High temperatures will cool closer to
seasonal averages midweek.

The primary issue in the short term is a small thunderstorm threat
across primarily the Lane and Linn County Cascades today and Tuesday.
This is in response to some moisture and instability sneaking its way
up into the region due to an upper level low pressure currently
spinning off the California coast. This low pressure is forecast to
slowly shift eastward over northern California over the next couple
of days. Even though it will technically shift closer to the region
during this time, it appears it will still be far enough away to have
few impacts and given thunderstorms remained east of the region
yesterday, inclined to believe that today won`t be too much
different. Model soundings from the Cascades support this idea as
well even the GFS model places QPF over eastern Lane County this
afternoon. The HRRR and NCAR ensemble do suggest that storms over
northern Lake and Klamath Counties or their remnants could sneak
their way towards Willamette Pass late this evening and overnight so
did keep a slight chance mention for this period, but even this
threat appears marginal.

As the aforementioned upper level low pressure shifts inland,
southwesterly to westerly flow aloft will strengthen slightly
Wednesday and Thursday. This should keep any thunderstorm chances
east of the Cascade crest. This will also help to produce more marine
clouds along the coast and lower Columbia River valley Wednesday and
Thursday, which should help to cool temperatures elsewhere closer to
seasonal averages. Both the GFS and EC suggest some light showers
could impact the northern coastal zones Wednesday morning, but given
500mb heights, this seems suspicious and will evaluate further with
the afternoon forecast package. /Neuman


.LONG TERM...No Changes. Previous discussion from Sunday afternoon
follows...Wednesday night through Sunday...Onshore flow from a series
of weak shortwave troughs will continue through next week. This will
maintain near normal temperatures with low clouds at the coast as
well as inland in the nights and mornings. No chance of precipitation
or thunder during this time. -Bishop


&&


.AVIATION...Much shallower marine layer this marine, generally
confined to the coastal strip. Areas of IFR cigs along the coast
through around 17Z. Expect stratus to push back onto the coast
between 03Z and 06Z Tue. Models hint that stratus may penetrate
more inland into the central coastal valleys late tonight.
Elsewhere, VFR to prevail through Tue morning.

Cannot rule out some TCU or CB developing in the Cascades E-SE of
KEUG this late this afternoon into the evening. Thunder is not
expected for any of our terminals, but is a possibility in the
Lane County Cascades, although the likelihood appears less
probable based on latest model guidance.

KPDX AND APPROACHES...VFR through Tue morning. Surface wind gusts
to around 20 kt late this afternoon through the evening. Weishaar


&&


.MARINE...Minimal changes to the current forecast. Strong north
wind continues over the waters today. Several models indicating
20-25 kt boundary layer wind speeds with gusts to 30 kt this
afternoon through late evening. A few gusts to 35 kt can be
expected over PZZ255 and PZZ275. Latest model runs suggest wind
speeds ease just a bit Tue, but will likely need a Small Craft
Advisory for the waters. The far north inner waters may fall just
short of advisory criteria. The pressure gradient and associated
surface and boundary layer wind speeds ease even more Wed.

Very steep and choppy sea conditions to persist for the next
couple of days. This is nearly a uni-wave pattern with spectral
guidance showing a wind wave component up to 8 ft at buoy 050
this afternoon, with a minimal background swell. Combined seas
could briefly reach 10 ft at times this afternoon through the
evening. Slightly less fetch and gradually decreasing wind over
the next couple of days will result in less wind wave component.
However, expect choppy conditions to continue through at least
mid-week. Weishaar


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Tuesday for Coastal Waters
     from Cape Shoalwater WA to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM
     this afternoon to 8 PM PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     7 AM PDT Tuesday.

&&



$$

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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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