597 
FXUS66 KPQR 182120
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
120 PM PST Sat Jan 18 2020

.SYNOPSIS...Plenty of clouds tonight into Sunday, as a weak system
lifts north across region. Then, dry weather returns on Sunday, along
with some sunshine and mild temperatures. However, a new  parade of
fronts will bring valley rain and mountain snow back to the region
for next week.
&&

SHORT TERM...Tonight through Monday...Finally, mild Pacific air has
arrived, as apparent from afternoon temperatures in the 50s along the
coast, and inot the south and central Willamette Valley. But, still
chilly over the Cascades and through the Columbia River Gorge. But,
temperatures have warmed into the middle 30s in the Columbia River
Gorge, with occasional light rain or drizzle reported. Still may have
few wet snowflakes mixed in the rain for that area, but little if any
additional impacts expected. 

Models continue to show a weak boundary lifting north across the
region later tonight into early Sunday morning.  All models have been
showing this, with best depiction in the 290K isentrope. Though
primary lift will be over the Coast and Coast range, and inland to
north of Salem. So, will boost PoPs and QPF a tad, with occasional
rain for that area, and only a chance of rain elsewhere. This lift
area will shift farther north early Sunday, with  rain mostly along
the WA coast and far northwest Oregon coast, and nearby coastal mtns.
QPF not all that much, with most areas will get 0.01 to 0.05 of an
inch tonight into Sunday am, though areas in the Coast Range and
Willapa Hills will get 0.10 to 0.20 inch. Will gradually decrease
those PoPs as the day progresses. 

Rest of the region should see a rather pleasant mid-January day, with
light southeasterly flow, variable clouds and temperatures in the
upper 40s to lower 50s. But, with snow on the ground, and return of
light offshore flow, areas in the Columbia Gorge and Hood Valley will
struggle to reach 40 deg.  

Increasing clouds for Sunday night as next system slowly approaches
from the west. But, this weakening front will bring spotty rain to
the coast by Monday am, with chance inland. With front weakening, may
not see much in way of rain east of the Coast mtns. Still mild, with
highs the middle to upper 40s. Snow levels stay 5000 to 6000 ft
Sunday night into Mon, but will lower closer to 5000 ft later Mon.

Next system of significance will arrive later Mon night and Tue, with
rain increasing. Snow levels initially at 4500 to 5500 feet Mon
night, but lower back to 3000 to 4000 feet on Tue. So, will see more
snow pile up in the Cascades on Tuesday.	       /Rockey

.LONG TERM...Tuesday night through Saturday...A progressive weather 
pattern continues next week with a series of fronts moving across 
the region every 24 hours or so. The models vary on the details of 
each system, challenging the forecast confidence on the timing of 
the fronts and consequential precipitation. 

GFS is an outlier for the first two fronts expected Tuesday night 
and Wednesday night so leaned towards a ECMWF/CMC blend. QPF is not 
impressive with the Tue system, but the modeled precipitable water 
values are close to 0.9 inch on Wednesday and there could be a 
healthy dose of Cascade snow at and above 3k feet. Determining 
actual snow amounts is very difficult that far out, but there is a 
chance for advisory snow amounts for the Cascades Wednesday 
afternoon through Thursday morning.   

Leaned towards the NBM for the subsequent weather systems due to the 
weighting towards ensemble members. The snow levels will rise to 
around 5k feet on Thursday as another fairly moist front is 
expected. The snow levels may briefly rise to 6000 feet with a moist 
warm front Thursday night, then settle around 5k feet Friday and 
next Saturday. ~TJ
&&


.AVIATION...Wide range of flight conditions early this afternoon,
with most areas MVFR. Remants of a frontal boundary over the 
region continues to weaken as it reaches the Cascades. Not 
expecting much change in overall flight conditions through the 
afternoon, with MVFR remaining the dominant category. Expect a 
gradual increase in VFR coverage late this afternoon through 
about 06Z Sun. Latest model guidance shows the remnant cold 
frontal boundary lifting north overnight into Sun morning, which 
may result in more IFR to MVFR conditions. There is also the
potential for IFR fog overnight, especially in the south half of
the forecast area. Offshore low-level flow will persist in the 
Gorge through Sun. Expect predominant VFR at the west end Sun. 

KPDX AND APPROACHES...MVFR will be the primary category through
Sun morning, with cigs 020-030. Improvement to predominant VFR 
Sun morning. LLWS looks to become less of a threat through the
afternoon and tonight as south wind gradually decreases at FL020.
Weishaar

&&

.MARINE...Wind speeds have eased since early this morning and
allowed the gale warning to expire as scheduled. Still getting
some local 35 kt gusts near shore, but do not expect these gusts
to persist beyond the afternoon. 12Z model runs show boundary 
layer wind speeds generally 15 to 25 kt through about 09Z Sun and
then possibly reaching 25 to 30 kt over the outer waters late 
tonight. Another frontal boundary moves through the waters late 
Sun night, which could produce marginal gale force gusts. Will 
cap gusts at 30 kt. There is a better chance for gale force wind
Mon night as a stronger frontal system traverses the waters. Have
indicated 35-40 kt gusts with this system. Generally followed the
ECMWF Tue and beyond. Another warm front is expected to move
through the waters late Tue night into Wed morning, which may
result in another round of gale force gusts. 

Combined seas close to 20 ft late this morning, with a
considerable wind wave component. The relatively short periods,
11 to 12 seconds, are creating very steep sea conditions. Wave
heights slowly decrease through tonight, but will remain in the 
12 to 14 foot range. Seas may slip just under 10 ft Sun night for
a short time, but then exceed 10 ft Mon morning. Seas expected 
to build into the mid to upper teens Tue. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 4 PM PST Sunday for coastal waters 
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 10 AM PST Sunday for Columbia River 
     Bar.

&&


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until noon PST today for Central 
     Columbia River Gorge.

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

     Winter Weather Advisory until noon PST today for Central 
     Columbia River Gorge.

PZ...Small Craft Advisory until 4 PM PST Sunday for coastal waters 
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 10 AM PST Sunday 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.