Area Forecast Discussion
National Weather Service Portland OR
914 PM PDT Sat Mar 25 2017

.SYNOPSIS...Showers will continue to decrease overnight tonight as
onshore flow decreases. The next rather strong frontal system will
spread rain into southwest Washington and northwest Oregon fairly
early on Sunday that will continue through the day. Look for breezy
conditions as well with snow in the Cascades. The associated cold
front will move onshore and through southwest Washington and
northwest Oregon late on Sunday. Onshore flow behind the front will
keep showers spreading onshore across the area through Sunday night
and Monday, with snow levels below the passes in the Cascades. A
system will brush the northern parts of the forecast area with
precipitation Tuesday, followed by another Wednesday and Thursday
that will affect all of the area. We may see some drying towards the
end of next week.


&&


.SHORT TERM...(Tonight through Tuesday)...Onshore flow was turning
more southerly and weakening tonight with just a few showers
remaining over the forecast area. These will continue to decrease
overnight before the approach of the next system.

The models show the next rather strong system approaching late
tonight, spreading rain and Cascade snow across southwest Washington
and northwest Oregon fairly early on Sunday and continuing through
most of the day Sunday. The associated cold front comes onshore and
moves through the forecast area late Sunday. It will be windy along
the coast ahead of the front, and breezy inland. Snow levels in the
Cascades will start out below the passes Sunday morning, may rise up
to near or just above the passes in Oregon in the afternoon, then
fall back below the pass elevations Sunday night and Monday as
onshore flow behind the front spreads plenty of showers across the
area. Have issued a snow advisory for the Cascades for Sunday through
Monday for all of this. From 6 to 14 inches are possible through
Monday, with the higher amounts at elevations above the Cascade
passes.

Showers decrease Monday night as the onshore flow decreases. The
models are coming in better agreement that the next system will
mainly go into western Washington on Tuesday, brushing the northern
half of our forecast area. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
(Tuesday night through Saturday) Upper-level pattern becomes more
amplified later next week, behind a trough that will bring more rain
Tuesday night into Wednesday, transitioning to showers on Thursday.
This means a ridge builds up over the Pacific Northwest Friday for a
dry and mild day. Models are in remarkably good agreement with this
ridge for how far out it is in the forecast period, increasing
confidence. Models however have the ridge flattening with an
approaching broad trough, with significant differences in timing
between the ECMWF (Saturday) and the GFS (Monday). Either scenario
will bring rain back to the area with the flattening of this ridge.
Snow levels generally hover around 4000 to 5000 feet, except for
Wednesday and Friday when they go up to 6-8000 feet. Temperatures
generally remain a little cooler than normal. -McCoy


&&


.AVIATION...VFR conditions should generally hold at most taf
sites until rain spreads eastward across the area between 12-18z
Sunday. Coastal locations will likely drop into MVFR conditions
for an extended period. Meanwhile, conditions should remain
predominantly VFR inland, but cigs may lower enough around 21z
Sunday that a few hours of MVFR conditions appears possible.

PORTLAND AND APPROACHES...Rain associated with an incoming front will
produce lowering cigs after 12z Sunday. East winds should keep
conditions predominantly VFR, but as the winds turn southerly around
~21z Sunday, there may be a short period of MVFR cigs. /Neuman


&&


.MARINE...An incoming front will bring strengthening south to
southeasterly winds to the waters tonight. Winds should rise
into Gale Force criteria of 35 to 40 kt across the outer waters
Sunday morning. The stronger winds will take a while to develop
across the inner waters. Given Gale Force winds struggled to
develop near the coast in the last similar frontal storm system,
confidence is a bit lower on whether or not they`ll actually
develop this time around, but will nonetheless, keep the Gale
Warning intact. Either way, seas should rise into the low to mid
teens midday Sunday and Sunday afternoon before falling back
below 10 ft Sunday night.

Weak high pressure will slowly build across the waters Sunday
night and Monday, which should result in less wind across the
waters. However, an incoming westerly swell will likely push seas
above 10 ft late Monday and/or Tuesday. In addition, another
frontal storm system, albeit weaker than Sundays, will move into
the waters Tuesday and/or Wednesday and bring gusty Small Craft
Advisory level wind gusts of 25-30 kt. High pressure looks to
then shift over the northeast Pacific and possibly bring us a
brief period of summer-like northerly winds late next week./Neuman


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 9 AM Sunday to 4 PM PDT Monday for
     Cascades in Lane County-Northern Oregon Cascades.

WA...Winter Weather Advisory from 9 AM Sunday to 4 PM PDT Monday for
     South Washington Cascades.

PZ...Gale Warning from 11 AM to 4 PM PDT Sunday for Coastal Waters
 from Cape Shoalwater WA to Florence OR out 10 nm.

     Gale Warning from 6 AM to 3 PM PDT Sunday for Waters from Cape
   Shoalwater WA to Florence OR from 10 to 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 1 PM to
   7 PM PDT Sunday.


&&

$$



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.