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Area forecast discussion 
National Weather Service Portland or
839 PM PDT Thursday Oct 23 2014

Synopsis...shower activity will decrease tonight as the air mass
slowly stabilizes. A warm front will spread light rain into SW Oregon
Friday morning and across northwest Oregon and SW Washington in the
afternoon and evening. A cold front will push inland Saturday
afternoon and evening...and possibly produce a brief period of strong
wind gusts along the coast. An upper trough will continue showers
through Sunday. Another frontal system is expected early next week.

&&
Update...a National Weather Service storm survey team determined that the tornado that
touched down in Longview Washington this afternoon was an EF-1. Radar imagery
shows showers that showers have eased since this afternoon...but are
still fairly persistent over SW Washington. There has been isolated
thunderstorms with some showers well offshore that are just entering
the northern Oregon coastal waters and have added isolated
thunderstorms for the waters and SW Washington coast for this evening. The
showers will decrease overnight in most areas...and remain on the dry
side through Friday morning. The exceptions will be the SW Washington coast
and the central Oregon Cascades. Rain will return from south to north
late Friday morning to the afternoon as a warm front lifts over the
area.

From previous short term discussion...the warm front moves into SW
Oregon Friday morning and then lifts north Friday afternoon and evening.
This will also induce offshore low-level flow through the Columbia
Gorge as pressure gradients increase. The north zones could be dry
for at least the first half of Friday ahead of the approaching warm
front. The low continues to deepen overnight Friday into Sat morning.

Major model differences for 12z Sat create a heightened level of
uncertainty regarding low strength...track and timing. The GFS is the
most consolidated with the surface low 12z Sat...while the European model (ecmwf) and
NAM have a more elongated low with multiple low centers. The latest
GFS is now the slowest with the low...with a 990 mb center near
Newport 18z Sat. The ecwmf and NAM have the main low center near the
far north Oregon or S Washington coast. The WRF-GFS valid 18z Sat has a small
core of 60-70 knots wind gusts along the S part of the central
coast...but by 21z wind gust speeds fall off to 40-50 knots. It also
shows a small core of 40-50 knots gusts in the central Willamette Valley
at 21z.

Despite all of model uncertainty...there is a higher
level of confidence regarding breezy to windy conditions developing
in the Willamette Valley Sat afternoon. At this point gusts to at
least 40 miles per hour look possible. An Special Weather Statement has been issued as a heads up to
this possibility. Will be keeping a close eye on this system and
model trends over the next 24 hours.

A broad upper trough...similar to what is over the area
today...settles over the region Sunday. This will bring additional
short-waves through the forecast area Sat night and Sunday. Snow
levels fall to near Cascade Pass levels Sunday. Tj/weishaar

Long term...Sunday night through Thursday...still an active weather
pattern continuing through early next week. After a brief drying
period late Sunday night through midday Monday...the next frontal
system...the remnants of Hurricane Ana...will move through the
region Monday night into Tuesday. Models are showing zonal flow
developing by the middle of the week...before weak ridging develops
next Thursday. All in all...expect wet and occasionally breezy
conditions as these fronts move through. /27
&&

Aviation...showers will continue tonight with VFR conditions
prevailing this evening. The lower air mass is quite moist and
with enough cloud breaks there could be some patchy fog or low
stratus late tonight and early Friday. Satellite trends indicate
there should be a decent amount of cloud cover to prevent
widespread low ceilings or fog from developing. Next front moving in
from the southwest Friday afternoon spreading rain from south to
north across the area. VFR conditions are expected though.

Kpdx and approaches...VFR prevailing through 12z with a 20 percent
chance of MVFR or lower ceilings from 12z-17z Friday.

&&

Marine...brief break in winds tonight and Friday as a low
approaches from the southwest. Models advertising offshore flow
through Friday evening the a quick switch to southerlies overnight
into Saturday. At some point on Saturday there should be gale
force winds as the low tracks through the area. Models suggest
landfall will occur somewhere between the north Oregon coast and
Vancouver Island. It seems somewhere in the middle is most likely.
A more southern track will likely result in higher winds across
the waters. Regardless of the tracks provided by various
models...gale force winds appear increasingly likely across the
waters late Saturday with a chance for low end storm force gusts
of 50 knots if the stronger and more southern track pans out.
Confidence is not particularly high at this point but enough to
continue the gale watch for Saturday. This will be refined as
models converge on a solution. Seas will almost certainly become
steep and wind dominated...possibly reaching upwards of 20 feet late
Saturday.

An active weather pattern capable of producing periods of hazardous
seas will likely continue into the weekend...but the details at
this point in time remain uncertain. Models do suggest seas will
relax in the Sunday/Monday time frame. /Neuman/mh

&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...gale watch from late Friday night through Saturday evening for
coastal waters from Cape Shoalwater Washington to Cascade Head or out
60 nm.

Small Craft Advisory for hazardous seas until 3 am PDT Friday
for coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Gale watch from Friday evening through Saturday afternoon for
coastal waters from Cascade Head or to Florence or out 60 nm.

Small Craft Advisory for rough Columbia River bar from
3 am to 7 am PDT Friday.

Small Craft Advisory for rough Columbia River bar from
3 PM to 8 PM PDT Friday.
&&

$$

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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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