Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251104

Area Forecast Discussion
National Weather Service Portland Oregon
403 AM PDT Tue Oct 25 2016

.SYNOPSIS...Deep low pressure below 980 mb centered well off southern
Vancouver Island and the northern Washington coast will gradually
weaken and move north through Wednesday. A second low closer to 990
mb is forecast to move north off the Oregon coast late tonight and
Wednesday for gusty coastal winds and more rain at times before
weakening as it makes landfall on Vancouver Island Wednesday night.
Another disturbance is expected Thursday. Another low is expected to
send surges of moisture into the forecast area this weekend.

.SHORT TERM...Today through Thursday...A deep low likely below 980 mb
was centered off Vancouver Island and the north Washington coast
outside 130W early this morning and will slowly weaken as it moves
northwest into the Gulf of Alaska today and tonight. The associated
cold front moved east of the forecast area overnight and we are under
south to southwest flow aloft with a few showers around. The best
coverage of showers early this morning has been over the coastal
waters and near the coast, and the Langley Hill National Weather
Service Doppler radar showed several storms earlier with rotating
updrafts for which we issued Special Marine Warnings. That activity
seems to have eased a bit now. Will keep a chance of thunder along
the coast through the morning per lifted index forecasts.

There is another comma cloud beginning to develop this morning out
around 37N/138W that the models develop into a low around 990 mb that
moves north along the Oregon coast just inside 130W late tonight and
Wednesday. The coastal gradient remains rather easterly again with
this storm and that may prevent high winds from developing, but still
expect some winds along the coast again. The strongest winds will be
over the coastal waters. The associated moist warm front with PWs
pushing 1.5 inches accompanied by 850 mb inflow winds of 60 to 70 kt
will lift north through our forecast area late tonight and Wednesday
morning with pretty substantial rains. The rains will not likely last
long enough for any river flooding, though local ponding of water is

The surface low weakens as it makes landfall into Vancouver Island
Wednesday night. The associated cold front lingers over southwest
Washington and northwest Oregon into early Thursday for decent rain
continuing before letting up on Thursday. One more upper level
disturbance will move through on Thursday and finally push the front
east of the forecast area later in the day. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Thursday night through Monday...Wet weather pattern looks to continue
into this weekend, with another trough dropping out of the Gulf of
Alaska Thursday into Friday. May get a brief break from the rain
Friday morning as shortwave ridging builds up ahead of the next
surface Low that comes up from the southwest. This Low looks fairly
weak, bottoming out in the high 990s to right around 1000 mb. Heavier
rain will impact southwest Oregon, but should be more moderate as it
moves farther north into Northwest Oregon and Southwest Washington.
Showers should linger across the area Saturday night through Sunday
morning before another weak system comes up the same track as the
last Low, along the track of the south side of the upper-level trough
sitting off the coast of Washington and Oregon. This one looks fairly
weak as well, only bringing moderate rainfall to our area Sunday
evening through Monday morning. This second surface low is more
associated with the upper-level trough, which shifts onshore Sunday
night into Monday, though another upper-level trough appears to come
in and take its place off the coast of Washington and Oregon for
on-and-off rainy weather to continue into early next week. -McCoy

.AVIATION...Predominately VFR today and tonight. Scattered showers
will continue across the forecast area this morning, with isolated
thunderstorms possible along the coast. Will see a brief period of
drier conditions this afternoon. However, another low pressure system
will spread rain across the region tonight, with brief period of MVFR
cigs and vsbys possible. Gusty south to southeast winds possible
through this afternoon.

KPDX AND APPROACHES...Predominately VFR. Isolated showers possible
this morning, with rain returning after 06Z. Gusty southeast winds
possible through 00Z. /64

.MARINE...A 974 mb low near 48N 132W will continue to slowly move
north and weaken later today. Expect southerly gales to continue over
the waters through around noon today, with the strongest winds over
the outer waters. Winds will subside below gales this afternoon as
the low pushes further north. Seas across the waters are currently in
the low 20s early this morning. Expect seas to slowly subside into
the low to mid teens this afternoon as the winds weaken. Seas may
briefly fall below 10 ft tonight.

A slightly weaker low, around 990 mb, is expected to move north along
130W late tonight through Wed. This will bring another round of
southerly gales to the outer waters, with seas climbing back into the
mid teens. Winds and seas finally fall below advisory criteria on
Thu, with much calmer conditions expected through Fri. /64

PZ...Gale Warning until noon PDT today for Coastal Waters from Cape
     Shoalwater WA to Florence OR out 60 nm.

     Gale Watch from Wednesday morning through Wednesday evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 6 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. is the U.S. government's official web portal to all federal, state and local government web resources and services.