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FXUS66 KPQR 290458 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
858 PM PST Tue Jan 28 2020

UPDATE: for evening aviation discussion

.SYNOPSIS...An active weather pattern will continue to produce above
average temperatures, periods of rain and high mountain snow through
the weekend. Cooler temperatures and lower snow levels appear likely
early next week, though.

&&

.SHORT TERM...Today through Friday...Water vapor satellite imagery
shows a shortwave trough over the Pacific Northwest digging
southeastward into the Great Basin. A trailing surface-850mb low
pressure is located off the north Oregon coast this afternoon.
Models are in good agreement it will continue to weaken as it pushes
ashore late this afternoon. Strong low to mid level flow in a
conditionally unstable environment will continue to wring out showers
to the south and east of the low pressure track late this afternoon
and early this evening. Snow levels are currently hovering between
3000-4000 feet this afternoon and will plan on letting the Winter Wx
Advisory for the Cascades expiring at 4 PM. Models are in good
agreement shortwave ridging will shift eastward towards the region
this afternoon and evening, which will result in a subsidence
inversion lowering to near 850mb by late this evening. This should
result in showers decreasing in both coverage and intensity through
that time.

The break in the wet weather will be short lived however. The next
storm system currently found in the Gulf of Alaska will drop
southeastward towards the region later tonight and Wednesday.
Models are in good agreement this will result in another round of
rain spreading southeastward across the region during this time.
This storm system appears progressive enough that hydrology impacts
should be limited, but brief sharp rises can be expected on our
smaller and faster responding rivers once again. Given the elevated
levels currently found on the Grays River, it will likely approach
minor flood stage once again tomorrow.

More uncertainty creeps into the forecast Wednesday night and
Thursday. Most model scenarios result in a warm front lifting back
northeastward across the region. While rain appears likely across our
northwestern zones regardless of model choice, particularly Thursday
afternoon and evening, there appears to be a decent chance that our
southern and inland zones could end up dry for most of the day. As a
result, have begun to lower PoPs, but even then rain chances may be a
bit overzealous.

Models then suggest an atmospheric river will take aim at western
Washington and Vancouver Island Friday. There is a lot of
uncertainty in where the southern extent of the precipitation will
end up. Current NBM guidance suggests areas north of Salem will end
up at least a little wet while areas south of Salem may in fact stay
dry the entire day. Anecdotally, it seems the southern periphery of
precipitation is often modeled too far south in these scenarios so
opted to keep temperatures on the warm side of model guidance. Our
current temperature forecast assumes that most areas from Portland
southward will dry out for at least a few hours Friday afternoon and
high temperatures will top out around 60F. /Neuman


.LONG TERM...Friday night through Tuesday...Guidance continues to
show the bulk of the moisture streaming into western WA late Friday
so will trend PoPs down for our southern zones Friday night into
early Saturday. Models then show the cold front sagging south across
the forecast area on Saturday which will result in another round of
valley rain and mountain snow. The upper level trough looks to then
swing inland late Saturday into Sunday which will keep unsettled
weather over the region, with snow levels lowering to the Cascade
Foothill and Coast Range elevations and temps falling from around 5
to 10 degrees above normal to near normal. A colder air mass looks
to then settle in over the region late Sunday into early next week,
with snow levels at night lowering to near the valley floor and
temps cooling to near freezing. This could result in a brief period
of lowland snow Sunday night, but due to model uncertainty will keep
a mix of rain and snow in the forecast. Despite the low snow levels
on Monday it also looks like rain chances will be waning so cannot
rule out the development of patchy fog, freezing fog, and frost
Sunday night. Transient shortwave ridging looks to then dry us out
even further late Monday, but with saturated soils and near freezing
temps expect areas of fog, freezing fog, and front across the
forecast area Monday night. Guidance then shows rain returning on
Tuesday as another disturbance moves across the Pac NW. /64
&&

.AVIATION...
-- Changed Discussion --
Stable air mass across the region this evening. Mix of
VFR with quite a bit of MVFR along the coast. Better inland, with
widespread low VFR with cigs generally 3500 to 5000 ft, and only few
pockets of MVFR.

Cconditions will gradually deteriorate later overnight, as a warm
front lifts across the region. Expect increasing MVFR and IFR along
the coast after 10Z, with areas of rain. But, main rain arrives after
15Z, with peristent upper IFR and lower MVFR along the coast. Farther
inland, will see cigs gradually lower to MVFR after 15Z, with spotty
light rain to north of Salem but staying VFR to the south. Rain
increasing inland after 18Z, with MVFR becoming dominant. Expect
widespread terrain obscurations in clouds.

KPDX AND APPROACHES...Mostly VFR until 12Z, with cigs 3500 to 4500
ft. But, cigs lowering to MVFR 12Z to 15Z, with spotty light rain.
Rain increasing by 18Z, with continued MVFR.      /Rockey
-- End Changed Discussion --
&&

.MARINE...Timely 19Z ASCAT pass revealed a surface low pres
center just north of Cape Disappointment. This can also be
surmised from the 20Z wind speed observations. Buoy 46029 had
minimal wind, generally around 5 kts, while 46050 reported gusts
just above 25 kt. The 12Z GFS, ECMWF and even the 18Z NAM did
not seem to have a good handle on location and depth of the
surface low. The back edge of the bent back occlusion appears to
have moved through the central and south Oregon waters as of
18Z.

12Z model runs show a gradually weakening surface gradient through
the evening, with wind gusts south of Tillamook Bar falling below
20 kt by 06Z Wed. The next warm front reaches the north waters by
12Z Wed. The NAM and GFS suggest boundary layer wind speeds of
30-35 kt over PZZ270 around 12Z. Gale force wind gusts look
likely for PZZ270 and PZZ250 beginning around 12Z and then
spreading into the northern portions of PZZ275 by 15Z. The RAP,
Hi-Res ARW, NAM and higher resolution HRRR suggest 30 kt boundary
layer wind speeds spreading over the majority of the area by 15Z
Wed. Will go ahead and issue gale warnings for the waters with
valid times 12Z-21Z for PZZ250 and PZZ270 and 15Z-21Z for PZZ255
and PZZ275. Confidence is a little lower south Heceta Head, but
feel the area from Cascade Head to Heceta Head has a high
probability of gale force gusts. Yet another warm front moves
through the waters Thu, but not anticipating gale force gusts
with this system as models show it more north. Eventually, a sharp
cold front swings through the waters Sat, which may produce near
gale-force northwest wind gusts.

Seas will hold steady in the 12-15 ft range through Wed and then
may reach 14-17 ft Wed evening through Wed night. Seas settle
back into the 11 to 13 ft range late Thu, but build into the
mid-teens Sat. There is concern for sneaker waves Thu with wave
heights 13-15 ft and relatively long periods of 15-17 seconds.
The weekend also poses potential sneaker wave concern, although
shorter periods of 12-13 seconds are expected. The predominant
swell direction will be 240-270 degrees through Sat. Models then
show a 13-15 ft northwest swell becoming the dominant train Sat
night through Sun. Weishaar


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST this afternoon for
     Cascades in Lane County-Northern Oregon Cascades.

WA...Winter Weather Advisory until 4 PM PST this afternoon for South
     Washington Cascades.

PZ...Small Craft Advisory until 4 AM PST Wednesday for coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 60
     NM.

     Gale Warning from 4 AM to 1 PM PST Wednesday for coastal waters
     from Cape Shoalwater WA to Cascade Head OR out 60 NM.

     Small Craft Advisory until 7 AM PST Wednesday for coastal
     waters from Cascade Head OR to Florence OR out 60 NM.

     Gale Warning from 7 AM to 1 PM PST Wednesday for coastal waters
     from Cascade Head OR to Florence OR out 60 NM.

     Small Craft Advisory until 4 PM PST Wednesday for Columbia
     River Bar.

&&


$$

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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.