Sneakerwave in Oregon, September 9, 2018

Area Forecast Discussion
National Weather Service Portland OR
222 PM PDT Sun Sep 9 2018

.SYNOPSIS...More like late September for next few days, with more in
the way of clouds and onshore flow. Next front will arrive tonight,
bringing light rain to much of Northwest Oregon and Southwest
Washington. Then, broad low pressure will arrive from the Gulf of
Alaska, maintaining onshore flow and a chance for showers through
much of the upcoming week. Will even see a chance for thunder midweek.

&&

.SHORT TERM...This afternoon through Wednesday...Weak high pressure
shifting east of the Cascades today ahead of an approaching cold
front. The cold front will arrive later today, with satellite imagery
already showing increasing mid and high clouds across the northern
half of the forecast area. Although there have already been some
sprinkles around, the bulk of the rain will reach the coast in the
next couple of hours and then it will move inland during the
overnight hours. Don't expect a ton of accumulation with mostly light
rain and amounts less than 0.10". The exception will be the north
OR/south WA coast and possibly the South Washington Cascades, which
may see up to 0.25" of rain. Rain chances taper some across the
southern half of the forecast area, but still expect far south areas
to get at least a few hundredths.

Keeping an eye on climate records, the Eugene Airport is only a few
hours away from breaking the Eugene record for number of days without
measurable rain. If KEUG doesn't get at least 0.01" of rain before 1
AM PDT (12 AM PST), the record will be broken. It'll be a close call.

The cold front will push east of the region Monday morning, but cool
onshore flow remains, keeping temperatures cool and a chance for
continues showers Monday. Although we'll be between weather systems
on Tuesday, a shortwave will keep shower chances around. Upped rain
chances some Tuesday and increased cloud cover. Also introduced a
slight chance of thunder for most of the local forecast area late
Tuesday afternoon and evening with a fairly strong cool pool dropping
south into the area along with a jet just to our south. Looks a bit
like a spring thunder pattern. Low pressure begins to drop out of the
Gulf of Alaska Tuesday and moves south just off the Oregon coast on
Wednesday, further increasing instability, so also put a slight
chance of thunder in for most of the area again late Wednesday
afternoon and evening. Didn't change temperatures much through
Wednesday, so still looking like cool days anywhere from 5 to 10
degrees below climate normals. Bowen

.LONG TERM...Wednesday night through Sunday...Models continue to
bring a cutoff low down the Washington coast Wednesday night
and over northwest Oregon Thursday morning. By this time most of
the energy is over northern California, but would expect some showers
in the area due to the cold pool aloft and moderate late
summer/early fall surface heating. Below normal temperatures will
continue until Thursday. The flow becomes more split on Friday as
the low weakens and the northern branch begins to dominate, thus
decreasing any threat of showers and bringing temperatures back to
near normal. A weak ridge builds over the area late Friday and
into Saturday and models do seem to have a consensus on that until
Sunday. Sunday another trough begins to approach the area and the
ECMWF a little faster. Although the models don't show any
precipitation for the area Sunday, with the faster ECMWF
solution could lead to some showers and have introduced a slight
chance in the forecast for the area. Schneider

&&

.AVIATION...VFR conditions across the region this afternoon with
variable high clouds. Expect increasing mid clouds at the coast
by evening and pushing into the interior tonight as the
associated front pushes into the forecast area. Breezy south
winds continue ahead of the front, especially for the coastal
areas. The front will push onshore with low MVFR to IFR ceilings
this evening. Low VFR to MVFR ceilings are possible along with
light rain tonight for the interior terminals, but rain and MVFR
conditions may be less likely south of KSLE. Rain will give way
to scattered showers and lifting ceilings early Monday.

KPDX AND APPROACHES...VFR through evening with increasing
mid/high clouds through the day ahead of an approaching front.
Light rain and possible MVFR conditions after 06Z with rain
turning to showers early Monday. Cullen

&&

.MARINE...South winds have increased across the waters as a front
pushes towards the Washington and Oregon coast. The current small
craft advisory for winds and hazardous seas remains on track and
will run through 9 PM for the northern zones. The associated low
lingers off the coast of British Columbia through Monday,
allowing a building 4 to 6 ft NW swell to cross the waters. This
will combine with building wind waves to maintain steep
conditions with waves of 6 to 9 feet and dominant period around 8
seconds. and dominant periods of 8-9 seconds. Winds and seas will
ease behind the front tonight, bringing an end of advisory
strength winds for the next few days. A 6 to 8 foot NW swell
will be fairly persistent through Wednesday due to the lingering
low with the dominant wave periods increasing to around 10
seconds Monday.   Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for Coastal
     Waters from Cape Shoalwater WA to Cascade Head OR out 60
     NM.

&&

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the CWA or forecast area.