Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 221015
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
215 AM PST Wed Jan 22 2020

.SYNOPSIS...A warm front will lift northeast into Washington later
today and tonight bringing another round of widespread rain along
with rising snow levels. A cold front then moves southeast through
the region Thursday and Thursday night for another round of rain,
and snow levels lowering again. The series of weather systems off
the Pacific and moving through the region continues through the
weekend.

&&

.SHORT TERM...Tonight through Friday...Moisture streaming up from
the subtropics just north of Hawaii, with precpitable water values
on the order of 1 inch, will keep a layer of deep moisture over the
Pacific Northwest through Thursday evening. A warm front off the
coast this morning is expected to lift northeast through the region
today and up into Washington tonight. A deep layer of moderate
isentropic lift today will bring widespread rain, along with snow
levels rising in the Cascades above pass levels late in the day.
Behind the warm front tonight, weaker moist isentropic lift
continues, most notably in the low levels as seen in the models
along the 285K and 290K isentropic surfaces. This will keep chances
for rain fairly high through tonight, especially across the northern
part of the forecast area. Will keep the winter weather advisory for
snow in the south Washington Cascades today where orogrpahic flow
also remains favorable, then as snow levels rise this evening expect
to be able to end the advisory.

As a progressive upper level ridge moves across tonight and heights
begin to fall again in advance of the next shortwave trough, the
frontal boundary will slowly move southeast across the forecast area
Thursday and Thursday night. Dynamics and the deep moisture will be
favorable for keeping pops high in this time frame. As a low end
atmospheric river with southwest 850 mb winds topping out at times
around 50 kt, expect some heavy rain to affect parts of the area at
times today through Thursday evening. Focusing boundaries appear
likely to move around enough to limit flood potential for much of
the region through Thursday, but the area most needing watching
appears to be the northwest part of the forecast area where the
prospects for uninterrupted rain and strongest moisture transport
are. Showers follow the cold front late Thursday night into Friday
as an upper level trough moves across the region, but as the deep-
layer available moisture decreases will see diminished chances for
rain, mainly for areas without favorable orographics.

.LONG TERM...Friday night through Tuesday...No changes. Previous
discission follows. Overall, models and their ensembles are in good
agreement an active weather pattern will continue to bring periods
of valley rain and mountain snow for much of the extended forecast
period. Weak shortwave ridging over the region early Friday evening
appears likely to shift east of the region quickly and will be
replaced by shortwave troughing over the northeast Pacific this
weekend. This will result in a front spreading widespread rain into
the area late Friday night into early Saturday. There is some hint
among the models that a weak low pressure may develop along the
trailing front off the northern California coast late Saturday. This
would likely result in the front and attendant band of rain stalling
out Saturday night into early Sunday. At this point, this appears
most likely to happen south of our CWA, but these have a tendency to
drift northward with time so it bears watching. Otherwise, the jet
stream appears likely to consolidate across the eastern Pacific
early next week, which will keep precipitation chances elevated.
/Neuman

&&

.AVIATION...Rain showers perist through the next 24 hours in
the post-frontal environment. Periods of reduced visibility is
possibe before 18Z Wed with heavier rain showers passing through.
Some lower IFR cigs are moving in along the central coast near
KONP, but generally conditions are VFR with a scattered layer
around 2500 ft in most places. Around max cooling (14Z Wed), cigs
may lower to MVFR however it would most likely be short lived. By
18Z Wed, onshore flow will usher in another cloud deck, most
likely to be MVFR in nature. This will also allow scattered
showers to persist through the remainder of the forecast. It is
at this time that conditions along the coast may deteriorate with
low cigs and reduced visibility.

A weak ridge aloft may allow for some fog to form in the early
morning hours on Wed (around 15Z) as temperatures cool near the
dew point temperature. The only hinderance will be a continued
southerly wind that may create enough mixing to keep fog at bay.
Through the day, a warm front will slowly move over the area
increasing southerly winds through the Willamette Valley, and
along higher terrain like the Coastal and Cascade range. Gusts
25-30 kt are possible inland, with higher speeds along the
coast. The gorge will remain fairly calm. Rain showers will
persist through this time with snow through the Cascades.

KPDX AND APPROACHES...Mostly VFR with periods of rain. Slight
chance of some localized ground fog, but most likely winds will
keep it from forming. By 18Z Wed, MVFR stratus is likely as a
weak front slowly moves over the area. Some directional wind
sheer is also possible at the terminal through 19Z Wed but
marginal so it wasn`t included in the TAF. -Muessle

&&

.MARINE...Expect an active pattern this week. Winds remain
ranging from 15 to 20 kt with gusts up to 30 kt today as zonal
flow persists. Seas around 14 to 16 ft will be the baseline
significant wave height through the next week with periods of
building seas with each passing system. Thursday morning will
bring yet another easterly moving front to the area. This
front has the potential to increase winds to gale force speeds
gusting to 35 kt, but at this time conditions are marginal at
best. The strongest chance for gale force winds will be in
central waters from 10 NM from shore westward. Seas will build
Thu night through Fri afternoon ranging from 16 to 18 ft, with
some model guidance suggesting near 20 ft. At this time
confidence remains low due to model variability with the low
position in which this front stems from.

Conditions will ease slightly through the weekend with no real
drivers for significant conditions which will ease seas to near
11 ft and winds to follow suit. A chance for a significant
weather system is possible next week, but it is too early to
have much confidence. -Muessle

 &&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Winter Weather Advisory until 4 PM PST this afternoon for South
     Washington Cascades.

PZ...Gale Watch from this evening through Thursday morning for
     coastal waters from Cape Shoalwater WA to Cascade Head OR
     out 60 NM.Waters from Cascade Head to Florence OR from 10
     to 60 NM.

     Small Craft Advisory until 7 AM PST this morning for Coastal
     waters from Cascade Head to Florence OR out 10 NM-coastal
     waters from Cape Shoalwater WA to Florence OR from 10 to
     60 NM.

     Gale Warning from 7 AM this morning to 4 PM PST this afternoon
     for Coastal waters from Cascade Head to Florence OR out 10
     NM-coastal waters from Cape Shoalwater WA to Florence OR
     from 10 to 60 NM.

     Small Craft Advisory until 7 PM PST this evening for Columbia
     River Bar.

     Small Craft Advisory from 2 AM to 6 AM PST Thursday for
     Columbia River Bar.

     Small Craft Advisory until 10 AM PST this morning for Coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 10
     NM.

     Gale Warning from 10 AM this morning to 4 PM PST this afternoon
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 NM.

&&


$$

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This discussion is for Northwest oregon and Southwest Washington
from the Cascade crest to 60 nm offshore. This area is commonly
referred to as the forecast area.


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