Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
239 PM PST Friday Mar 7 2014
Synopsis...an upper level ridge that built along the Pacific
northwest coast today will continue to move onshore tonight...
bringing with it drying weather and decreasing clouds...but also
areas of night and morning fog and low clouds. The next fairly strong
and wet Pacific frontal system will begin spreading into southwest
Washington and northwest Oregon Saturday afternoon but especially
Saturday night...with more significant rainfall...with high snow
levels...and possibly strong winds near the coast and over the
coastal mountains. The associated cold front will move east of the
area on Sunday morning. A trailing cooler disturbance will bring more
rain and some mountain snow to the area Sunday night and Monday. An
upper ridge may then bring a few days of drier weather after Monday.
Short term...an upper ridge building along the coast will continue
to move onshore tonight. This will bring more areas of clearing
tonight...but the moist low level air mass with not much low level
flow will lead to areas of fog and low clouds developing overnight
and continuing through Saturday morning.
Attention then turns to the next system...currently out near 135w.
This is a very moist front again...and it should begin spreading
onshore Saturday afternoon...and especially Saturday night into early
This front should be strong and wet enough for significant rises on
area rivers again...with 850 mb winds near 70 knots and precipitable waters over an
inch. We will see if a couple of rivers could get close to flood
stage again...as several may reach bankfull levels. The Grays River
and the Nehalem river would be the two of most concern...and possibly
the Clackamas river.
We will also have fairly strong winds again with this system...with
boundary layer winds over 40 knots and 850 mb winds near 70 knots. This
should be enough for high winds again along the coast and over the
Coast Mountains late Saturday and Saturday night. Will be issuing
high wind watches for the coast and coastal mountains with this
forecast package. It appears to weaken enough that the winds may not
be as strong in the valleys for this event especially later Saturday
night with the front... but it should still be pretty breezy
overnight Saturday night.
Snow levels stay high enough for no issues with snow in the Cascades.
The front pushes east through our area Sunday morning... with
decreasing precipitation through the day.
The models show a trailing upper trough and area of showers moving
through southwest Washington and northwest Oregon Sunday night and
Monday...with increasing showers and snow levels lowering to near
pass elevations on Monday. Tolleson
Long term...Monday night through Friday...after a lingering threat
for showers late Monday and some orographically enhanced showers
into Tuesday morning...there is good model agreement amplifying an
upper level ridge over the Pacific northwest Tuesday and Wednesday.
Given the recent batch of moisture and clearing...may see some
patchy morning/evening valley fog develop Tuesday and Wednesday
since surface pressure gradients weaken as well. Most recent model
runs have downplayed the next frontal system expected Wednesday
night. The 07/12z GFS still digs the trough axis further south into
the forecast area Thursday...but has now lifted the threat more into
Canada similar to what the European model (ecmwf) consistently shows. Once we get
into late next week...there are several model discrepancies. Went
more towards climatology for the remainder of the extended since the GFS
has a ridge building over US...while the European model (ecmwf) has a front moving
Aviation...VFR conditions...moist low levels and light winds should
lead to IFR and MVFR conditions developing tonight. An incoming
frontal system will cause conditions that are not already down due to
fog and low clouds...to gradually deteriorate Saturday into
MVFR...with IFR conditions possible along the coast.
Kpdx and approaches....VFR conditions will likely give way to
deteriorating conditions overnight as fog and low clouds develop. An
incoming frontal system Saturday should bring MVFR conditions to the
terminal late Saturday. /Neuman
Marine...light winds this afternoon will gradually strengthen across
the outer waters tonight with gusts to 25 knots possible.
Meanwhile...seas should continue to subside from near 9 to 10 feet this
afternoon to 7 feet Saturday morning.
An incoming frontal system will cause winds to strengthen further
Saturday. Gale force wind gusts of 35 to 40 knots appear increasingly
likely across the outer waters midday Saturday. These higher winds
should spread into the inner waters towards late afternoon and early
evening. At which point...a coastal jet will likely develop producing
45 knots gusts within 20 nm of the coast. This will cause seas to rise
quickly into the middle to upper teens Saturday evening. I do expect
seas to relax fairly quickly late Saturday night into the low teens
as winds subside overnight.
Otherwise...high pressure with just a couple weak passing storm
systems will bring quieter winds and seas through midweek. An
incoming swell may cause seas to push 10 feet late next week. /Neuman
or...high wind watch from Saturday afternoon through late Saturday
night for central Oregon coast-north Oregon coast.
High wind watch from Saturday afternoon through late Saturday
night for central Coast Range of western Oregon-Coast Range
of northwest Oregon.
Washington...high wind watch from Saturday afternoon through late Saturday
night for South Washington coast.
High wind watch from Saturday afternoon through late Saturday
night for Willapa Hills.
Pz...Small Craft Advisory for winds from 10 PM this evening to 10 am
PST Saturday for waters from Cape Shoalwater Washington to Cascade
Head or from 10 to 60 nm-waters from Cascade Head to
Florence or from 10 to 60 nm.
Gale Warning from 10 am Saturday to 1 am PST Sunday for waters
from Cape Shoalwater Washington to Cascade Head or from 10 to 60 nm-
waters from Cascade Head to Florence or from 10 to 60 nm.
Small Craft Advisory for winds from 4 am to noon PST Saturday
for coastal waters from Cape Shoalwater Washington to Cascade Head
or out 10 nm-coastal waters from Cascade Head to Florence
or out 10 nm.
Gale Warning from noon PST Saturday to 5 am PDT Sunday for
coastal waters from Cape Shoalwater Washington to Cascade Head or
out 10 nm-coastal waters from Cascade Head to Florence or
out 10 nm.
Small Craft Advisory for rough Columbia River bar from 7 PM to
11 PM PST this evening.
Small Craft Advisory for rough Columbia River bar from 8 am to
noon PST 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.