Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 211606
Area Forecast Discussion
National Weather Service Portland Oregon
906 AM PDT Fri Oct 21 2016
.SYNOPSIS...The remains of the front that brought rain to southwest
Washington and northwest Oregon Thursday persisted over the southeast
part of the forecast area this morning but will continue to weaken
and dry out today. An area of showers associated with an offshore
upper level low will reach the coast today and spread some showers
inland later today and this evening especially from about Salem
northward. The next decent front will spread more rain onshore and
inland Saturday night and Sunday, followed by another front late
Sunday night and Monday. A broad area of low pressure will remain off
the coast and continue to produce unsettled weather at times in
southwest Washington and northwest Oregon next week.
.SHORT TERM...Today through Sunday...The KRTX radar is back in
service but additional finishing touches will be done today.
The front from Thursday was still hung up in eastern Lane and Linn
counties and this is the area with the greatest coverage of
precipitation this morning. As expected yesterday, this front will
continue to weaken and dry out through the day today.
The remainder of the area has plenty of clouds with just an isolated
shower here and there, mainly coming off the coast range. There is
some local fog as well this morning.
The models and satellite imagery show some showers and instability
associated with the main low offshore will spread onshore this
afternoon and evening. The best coverage will be along the coast
especially north, and in the northern valleys. There is a chance of
thunder along the north coast today and into the Kelso area late this
afternoon and evening, but probably not farther south.
We will be in between systems later tonight and most of Saturday with
just a few residual showers if that. Under the somewhat stable
conditions we will probably see more areas of fog and low clouds
later tonight and Saturday morning.
The next pretty decent front is expected late Saturday near the
coast, spreading inland Saturday night. The front will still be over
southwest Washington and northwest Oregon Sunday, weakening and
moving east in the afternoon. This should produce a decent shot of
some rain. Tolleson
.LONG TERM...No Changes. Previous discussion follows...
(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...Rather dankish day across the region, with mix of flight
conditions. Generally...MVFR with patchy fog, but more widespread IFR
clouds and fog in Willamette Valley to south of Portland, with mid
and high clouds above. Will see a slow improvement to VFR across
region through 21z...with slowest to modify being those in Willamette
Valley. Weak front will push across area this evening, and should
bring back MVFR cigs. Still looks like front will push most of the
low level clouds out of the region later tonight. But with better
potential of clearing, suspect will see widespread fog and low
stratus later tonight persisting well into Sat.
KPDX AND APPROACHES...Low MVFR conditions persisting this am. But
with high clouds on the increase, clouds will be slower to break up.
Should see break up of lower clouds 19z to 21z...with VFR afterwards.
But, weak front this evening with MVFR returning. Rain ends around
midnight, with clouds breaking up somewhat. Am expecting another
round of fog and stratus after 10z. rockey.
.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 to be strongest of the fronts, with
southerly gales likely. Rockpyle
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 PM 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.