Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 281517
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
817 AM PDT Tue Mar 28 2017

.SYNOPSIS...A warm front approaching WA and northern OR will
bring increasing chances for rain to the region today and tonight. A
cold front will move se through OR Wed, turning rain into showers
Wed and Wed night. Showers will continue through Thu, but drier
weather is in store for Fri as a ridge of high pres moves across.
&&

.SHORT TERM...(Today through Thursday)..
Occasional light rain over the northern zones today, especially north
of Tillamook and over the coast and coast mountains. Will boost PoPs
for those area a bit more for today. Also, bit better threat of light
rain inland today, but will keep lowlands in 40 to 50 percent chance
today.

Only other change is to boost QPF for tonight and into Wed. This
mainly due to decent precipitable water plume, of 1.0 to 1.3 inches
offshore aimed at region for later today and tonight. So, seems like
good rainfall for a bit, with 1 to 3 inches tonight and Wed for the
coast mountains, and generally half to locally 1 inch for interior
lowlands. Otherwise, wet night and generally wet Wed on tap.

Previous discussion as follows:  A surface ridge of high pres
over western Oregon early this morning is expected to shift into
southern Oregon today and tonight. This will eventually deepen the
onshore flow and moisture over the region. A warm front is expected
to approach the region late tonight as a low pres center heads up
towards Vancouver Island Wed morning. Isentropic lift will increase
and lower ahead of the warm front. Today, the moist isentropic lift
will tend to be weak and primarily confined to mid levels. Prefer to
keep some mention of light precipitation over all but the far
southern part of the forecast area given the current distribution
of light rain over the area and the weak lift. Tonight pops quickly
increase to categorical as models develop stronger moist isentropic
lift with a strengthened sw flow on the order of 40 to 50 kt along
the 290k isentrope just a few thousand feet msl. With plenty of
clouds and the approach of the warm front, temps should remain mild
tonight with snow levels rising well above Cascade passes by Wed
morning.

Models agree on dragging the trailing cold front se through the
forecast area Wed and Wed evening. With deep moisture preceding the
front chances for rain will remain categorical Wed morning, then
remain high across the south part of the area Wed afternoon and
evening as the baroclinic zone may be a little slow to clear the
region as the front becomes closer to parallel with the upper flow.
Behind the front a cooler air mass moves in, with the cold upper
trough moving through late Wed night into Thu morning. Expect
showers to become more orographically favored once the upper trough
passes Thu morning.

.LONG TERM...(Thu night through Monday)...No changes. Previous
discussion follows. Model agreement is better through Fri and Sat,
with a more progressive pattern over the region. Models continue to
show ridging over the region by Fri, with dry and mild temperatures.
Still differences in the models, but will maintain dry weather into
Sat. But, will trend back to some chance of showers for Sat night
and Sun as will see another front shift across the region at that
time. With the progressive pattern, will see fronts moving across
the region about every 2 days. So, after Sunday, will transition to
another decreasing shower day on Monday, with potentially another
dry day or two to start next week. However, since it is spring and
Mother Nature can get feisty at times, will keep some mention of
showers to start next week./mh  Rockey.

&&

.AVIATION...A warm front moving onshore this morning will bring
light rain or drizzle and a mix of VFR and MVFR to SW Washington
and far NW Oregon this morning. There may be brief improvement to
VFR for inland locations as the warm front lifts north between
16 and 18z. However, an approaching cold front will continue a
mix of MVFR cigs for coastal areas. The trailing cold front will
move NW to SE across the area late tonight into Wed morning for
rain and widespread MVFR conditions. Gusty south winds will
persist at coastal TAFS through tonight.

KPDX AND APPROACHES...Light rain or drizzle and occasional MVFR
cigs expected through around 15Z as a warm front moves north of
the area. Conditions should improve to VFR after 16Z. Rain will
increase again between 06Z-12Z Wednesday and MVFR cigs will
return. ~TJ

&&

.MARINE...A warm front is moving through the waters this morning.
The trailing cold front will move into the waters north of
Cascade Head early this afternoon...and south of Cascade Head
late this afternoon. A low moving along the front will stall the
front over the waters tonight and early Wednesday morning before
the front moves onshore early Wednesday afternoon. South winds
will increase as the low nears the waters with gale force gusts
expected late this evening through early Wednesday morning. Have
upgraded the Gale Watch to a Gale Warning. The winds will turn
westerly and subside behind the front on Wednesday.

The seas are a combination of two west swell trains today...one
at 18 seconds and the other around 12 seconds. The longer period
swell will become the dominant wave train by Wednesday morning.
Steep wind waves will contribute to the mixed seas in response to
the increasing winds. Combined seas are expected to build to
around 15 ft tonight.

High pressure will build Wednesday night and Thursday and hold
through Friday for northwest winds and subsiding seas. Seas
subside below 10 ft on Thursday then remain between 5 and 7 feet
through Saturday. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 10 PM PDT this evening for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Gale Warning from 10 PM this evening to 7 AM PDT Wednesday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Small Craft Advisory for hazardous seas until 10 PM PDT this
     evening for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 9 AM
     PDT Wednesday.

&&



$$

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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.


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