Area Forecast Discussion
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FXUS66 KPQR 211039

Area Forecast Discussion
National Weather Service Portland Oregon
339 AM PDT Fri Oct 21 2016

.SYNOPSIS...A stationary front continues to bring occasional rain to
Eugene and the Oregon Cascades this morning. Otherwise, much of the
forecast area is dry but cloudy with patchy valley fog. Rain over the
south part of the district should taper off today as the front
weakens. Another trough approaching the Pac NW coast is expected to
push more showers onshore this afternoon and evening. Showers should
diminish again tonight, with patchy fog expected again in the valleys
Sat morning. Saturday should be mostly dry though fog may be stubborn
in some valleys. Rain chances increase again Saturday night and
Sunday as the next front moves toward the coast. This front is
associated with a stronger low pressure system which will eventually
settle off the Pac NW coast early next week...keeping weather
unsettled at times well into next week.


.SHORT TERM...Today through Sunday...KRTX radar is back in service
today, and it shows some of the persistent light rain affecting the
Eugene area and the Oregon Cascades...mainly south of Mt Jefferson.
The rain is associated with the frontal zone which moved across the
CWA Thursday, stalling near its current position yesterday evening.
This stationary front will slowly dissipate over the next 6-12 hours
as it becomes increasingly removed from favorable upper level
dynamics. Meanwhile the next upper disturbance will push a sfc trough
onshore into western Washington and NW Oregon, enhancing showers late
this afternoon into this evening. Am a bit unimpressed with the
thunder threat, with 500 mb temps not falling below -20 deg C until
this afternoon and only falling to around -24 deg C this evening...
after solar heating has ended for the day. However we decided to
leave the slight chance mention in the forecast for the North Coast
and adjacent waters this afternoon and evening, as latest lightning
detection shows a handful of strikes about 100 miles off the WA

Showers associated with this afternoon`s disturbance will taper off
overnight, with some clearing possible as weak high pressure builds
into western Oregon. This could yield some areas of dense fog, but a
lot will depend on just how much clearing occurs. SW flow aloft could
still stream plenty of higher clouds across the district which would
act against fog formation. Kept coverage patchy for now, but there
are certainly some scenarios where we could end up needing Dense Fog
Advisories for inland valleys Saturday morning.

Saturday will be generally be the driest day of the next few, with
some peeks of sunshine likely for most. Depending on how widespread
morning fog is, it could take some time Saturday for the valleys to
break out of the fog. Regardless, inversions will probably hold
valley temperatures a couple degrees below MOS values. Clouds likely
start increasing again later Sat/Sat night as a developing low near
130W pushes an occluding front toward the coast. Light to moderate
rain will probably push onshore by Sat evening, then across much of
the forecast area Saturday night into Sunday. Given that this front
will be occluding and stretching as it comes in, QPF will probably be
rather low...generally less than 1 inch through Sunday with most
inland valleys struggling to receive much more than 0.25".
Nonetheless, Sunday will probably be a damp and cool day with
occasional light rain for most.  Weagle

.LONG TERM...(Sunday night through Thursday)...Models and ensembles
continue to show general agreement that longwave troughing will
linger between 140W-130W well into next week. Part of the deep upper
trough presently pushing S-SE across Alaska is expected to shear off
and eventually develop into a large sub-980 mb low pressure system in
the general vicinity of 45N/133W Sunday night into Monday. This
system will push another occluding cold front toward the coast
Monday, with the 00z GFS showing 50-60 kt reaching as low as 925 mb.
At this point it appears the low will be far enough offshore to keep
the stronger winds offshore, though our beaches and headlands may
flirt with High Wind Warning criteria if the front can get a coastal
jet going early Monday morning. The large parent low offshore is
expected to linger into midweek, then either fill or lift N-NE into
British Columbia. This will keep the main baroclinic zone draped over
the Pac NW well into next week...which means rain chances will
continue through at least Wednesday. Picture is less certain late
next week as some models suggest somewhat of a cutoff system trying
to develop off the CA coast, while others try to keep the pattern
more progressive.  Weagle


.AVIATION...Although there are broken high clouds streaming across
SW Washington and NW Oregon, recent rains have left the low level
airmass moist enough low stratus and patchy fog to form this
morning. Expect mainly IFR or low MVFR conditions through around
18Z. A stalled frontal boundary over Lane County will bring the
chance showers to KEUG through the morning. Conditions should
gradually improve to mainly VFR around midday and remain VFR
through this afternoon. A weak front will move onshore this
evening, bringing light rain chances along with the potential for
the return of MVFR cigs. Then scattered clouds overnight may allow
for more low stratus and patchy fog early Sat AM.

KPDX AND APPROACHES...Expect IFR stratus to remain through mid-
morning. Cigs may lift to low MVFR by 16Z-18Z, then improve to VFR
by midday. VFR conditions expected for the afternoon. Then light
rain and potential for MVFR cigs arrives this evening. Scattering
clouds overnight may allow for more low stratus or fog early Sat
AM. Pyle


.MARINE...Winds are southerly at 15 kt or less this morning. A
weak cold front will move through the waters today, leading to a
slight increase in winds. Expect they will remain generally less
than 20 kt, but a few gusts to 25 kt are possible over the
northern waters. A longer period westerly swell will arrive this
evening, pushing seas up into the low teens. Seas likely remain
above 10 ft through Sat. A stronger frontal system will arrive
late Sat. Expect at least solid small craft winds from later Sat
afternoon through early Sun AM, with the potential for low-end
gales. Then a series of stronger fronts will arrive every 24 hrs
or so from Sun through the first half of next week. The Sun system
looks like the strongest of the bunch at this point, with gales
looking likely. The 00Z GFS and ECMWF suggest the potential for
storm force winds Sun night. Will hold off on going that high in
the fcst for now, keeping gusts at solid to high-end gales. Pyle


PZ...Small Craft Advisory for hazardous seas from 5 PM this
     afternoon to 5 PM PDT Saturday for Coastal Waters from
     Cape Shoalwater WA to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 6 PM
     this evening to 6 AM PDT Saturday.



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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.