Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 291048
Area Forecast Discussion
National Weather Service Portland OR
345 AM PDT Wed Mar 29 2017
.SYNOPSIS...A warm front will move east across the region this
morning, with a cold front following and moving southeast through SW
Washington and NW Oregon later today. This will turn the rain into
showers later today, then showers will conitnue into Thu as an upper
level trough of low pressure moves across the Pacific NW. Fri is
expected to be dry as high pres moves across the region, then
chances for rain return for the weekend as the next system moves in.
.SHORT TERM...(Today through Friday)...Moist isentropic lift, best
seen along the 190k isentrope continued early this morning across
most of the forecast area ahead of a warm front approaching off the
coast. The isentropic lift will weaken considerably this morning as
the warm front pushes inland. The parent surface low off the WA
coast is expected to lift ne across Vancouver Island today. A cold
front trailing the low will push se across the forecast area today,
slowing as becomes more parallel to the upper flow late today. With
deep moisture in the air mass preceding the cold front, the chances
for rain will remain high. Behind the front air mass will turn more
showery, with low level flow turning sharply to the nw. The trailing
upper level trough is expected to move across Thu morning, with
moisture will generally be limited to low levels below about 10k
feet. Once the upper trough passes, shower activity is expected to
become more reliant on orographic lift and thus will tend to become
more tied to the upwind side of the mountains.
Thu night into Fri a ridge of high pres at the surface and aloft
pushes e into western Oregon and Washington. Subsidence will
stabilize the atmosphere bringing an end to the showers. Low level
will be slow to dry out though as a low level offflow never really
.LONG TERM...(Fri night through Tuesday)...No changes. Previous
discussion follows. Model agreement is better through Sat,
with a more progressive pattern over the region. Models continue to
show ridging east of the region on Saturday. Still looks dry and mild
on Saturday, with just increasing mid and high clouds. Now, while
there are still differences in the models, will have to keep some
minor threat of showers in forecast for Sat night into early next
.AVIATION...A cold front will be pivoting onshore this morning,
bringing steady rain and deteriorating flight conditions across
the region. MVFR conditions have developed on the coast over the
past several hours, while the interior remains VFR at this time.
Expect MVFR over the interior as well by around 15Z. There could
be localized IFR as well, with the best chances at KONP and KHIO.
Expect little chance through the afternoon as the front moves
very little. A secondary cold front will move through this
evening, with rain tapering to showers behind the front. Expect
conditions to become predominantly VFR behind the front with
occasional MVFR in heavier showers.
.PDX AND APPROACHES...Expect steady rain through today as a front
stalls over the region. VFR early this morning should deteriorate
to MVFR by around 15Z with conditions changing little through the
afternoon. A cold front will move through this evening. Rain will
taper to showers and expect conditions to improve to VFR behind
the frontal passage. Pyle
.MARINE...A surface low pres is currently centered around
47N/129W. This low will move NE and onshore on Vancouver Island
later this morning. Southerly winds associated with this low have
picked up overnight, and we are now seeing borderline gale force
winds at buoy 46050. Expect winds generally 25 to 30 kt with
gusts to 35 kt through mid-morning. There may be a few gusts to
40 kt south of Cascade Head and within 20 nm of shore as some
coastal jet enhancement may occur. Winds will become W-NW and
slacken later this morning and especially this afternoon as the
cold front moves onshore.
Higher pres will become established over the NE Pac later tonight
and Thu, and will remain through Fri. There may be some
borderline small craft advisory NW winds over the northern
waters later tonight into Thu morning. But otherwise, expect
fairly benign conditions during this time. A weak front will move
through the waters Sat, which will briefly turn the winds
southerly and may bring some gusts of 20 to 25 kt. Northerly
winds return Sun and Mon and may be gusty at times.
Seas will remain in the 12 to 14 ft range through tonight. Long
period westerly swell will combine with a significant southerly
wind wave component to produce chaotic seas. The seas will
subside tonight and Thu, dropping below 10 ft by around midnight.
Seas then remain below 10 ft through the next several days. Pyle
PZ...Gale Warning until 11 AM PDT this morning for Coastal Waters
from Cape Shoalwater WA to Florence OR out 60 nm.
Small Craft Advisory for Rough Columbia River Bar until 11 PM
PDT this evening.
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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.