Area Forecast Discussion
Issued by NWS Portland, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KPQR 180402
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
801 PM PST Sat Feb 17 2018

.SYNOPSIS...Reminder that it is still winter, with shot of colder air
for this week. Will see heavy snow in the mountains tonight and
Sunday, with snow at times down to the lower elevations of the
region. Dry weather on Mon and Tue, then will bring back a minor
threat of precipitation for the region. But, not strong threat, as
overall will stay on cool and drier side for the coming week.

&&

.SHORT TERM...Tonight through Monday...Have added a slight chance for
thunderstorms over the coastal waters and along the immediate coast
early Sunday morning through Sunday evening when the low is expected
to move over the area. Colder air is starting to move into extreme SW
Washington and extreme NW Oregon this evening and snow levels are
lowering. Surface observations, the Astoria Wind profiler, and local
web cams suggest that the snow level for the coast and northern coast
range (including the Willapa Hills) are between 2500 and 3000 feet.
The coldest air is expected later tonight and will push the snow
levels even lower. Did not change timing or amounts of low elevation
snow with the evening update, but did increase pops slightly. ~TJ

Previous discussion from 238 PM follows. Vigorous upper level trough
now digging into the Pac NW. Cold front has pushed inland today, with
breezy southwesterly winds and somewhat mild conditions at the
moment, with temperatures in the lower to middle 50s inland. Decent
onshore flow, with winds gusting 25 to 35 mph across the lowlands,
and 35 to 50 mph over the higher terrain of the Cascades. Said winds
will ease a bit this evening, but will stay breezy over the higher
terrain through Sun afternoon.

Much colder air aloft will push inland tonight and Sun, allowing snow
levels to tumble down to around 500 to 1000 feet by Sun am.  Plenty
of showers to push across region tonight, and with snow levels
lowering, think will have good chance of getting some sticking snow
down as low as 500 to 800 feet later tonight into early Sun am,
mainly in the Coast Range to Portland and northward.

Next upper disturbance now about 100 miles off the north tip of
Vancouver Island. Models insist this low will push inland over south
Washington or northwest Oregon later Sun am, then across to north
Oregon Cascades in the afternoon. Thicknesses and temperature profile
support snow fairly low to east of this low, but not sure if will get
all way to valley floors. Will be close, so will keep snow levels at
400 to 600 feet for Cowlitz lowlands southward through
Portland/Vancouver metro, and 700 to 1000 feet south of Portland down
to Salem and Eugene. At moment, leaning to 1 to 3 inches of snow for
areas above those levels, with an inch or less below.  But, for most
areas below a 500 to 800 feet levels, snowfall will be spotty or
hit-n-miss as will depend on where showers develop/move, with brief
accumulations that will likely melt off a bit after it accumulates on
Sun.

As the day progresses, air mass will cool further, with snow levels
gradually lowering to valley floors by evening. Suspect this may be
best time for lowland accumulations, but likely an inch or possibly 2
incs for those areas, but may be in question as precipitation will be
gradually decreasing.

Snow will still be falling over the higher terrain, with another 10
to 20 inches of snow in the Cascades. Travel over the Cascades will
be difficult and slow at times, due to combination of heavy snow at
times along with low visibilities from blowing/drifting of snow.

Have also issued various Winter Weather Advisories for snow for many
areas. Also, will maintain Winter Storm Warnings for the Cascades
where will see another 10 to 24 inches of snow through Sun night.

Cold front will gradually push south across the region Sun night,
with precipitation decreasing. But, will see much colder air push
into the region, with temperatures dropping into 20s. Any moisture
on roadways will likely freeze, with widespread icy spots a good bet
throughout the region Sun night into Mon am.

Still cold on Mon, with highs generally in the 30s for the lowlands,
and 20s in the Cascades.
/Flanders

.LONG TERM...No Changes. Previous discussion follows...Tuesday night
through Saturday...Expect the cold pattern to continue through the
middle portion of next week before some slight moderation in
temperatures later in the week. Forecast models continue to display
somewhat different scenarios with various disturbances moving near or
through the region and as such, confidence in the details
(specifically, precipitation) remains somewhat lower than normal
through the long term forecast period. The mean longwave pattern
remains consistent with an amplified upper ridge remaining over the
east-central Pacific and generally northerly flow across the Pacific
Northwest. Thus, the key factor will be determining if a more
northeasterly or northwesterly component to the flow pattern aloft
develops. Maintained some mention of PoPs late Wednesday and early
Thursday, but at this point expect the snow level to remain around
1,500 feet or so through this time period. Otherwise, below normal
temperatures and only occasional infusion of moisture can be expected
through next week. Cullen
&&

.AVIATION...Post-frontal showery air mass over the area this
evening. Generally VFR inland and a mix of MVFR and VFR for the
coastal TAF sites. Do not see much change in overall conditions
through about 12Z Sun. A surface low dropping south along the
Washington coast will be near KAST by 18Z. Expect deteriorating
flight conditions after 12Z from north to south. Northern TAF
sites, such as KAST, KUAO, and KSLE may see a rain/snow mix 12Z
to 18Z. The low continues to slide south Sun afternoon and
evening, with higher probability of IFR conditions as showers
fall more as snow, with the exception of the Central Oregon
coast.

PDX AND APPROACHES...VFR at the terminal and vicinity as of 04Z
and this will hold through at least 12Z. Flight conditions lower
to at least MVFR shortly after 12Z, with the potential for
rain/snow mix at the terminal, KTTD and KHIO through 18Z.
Generally MVFR 18Z through 02Z Sun, with areas of IFR. Higher
probability of snow after 00Z Sun. Any snow that occurs in the
morning is not expected to impact runways. Weishaar

&&

.MARINE...Wind speeds have eased a bit this evening, but buoys
continue to show 30-35 kt gusts. Wind will strengthen Sun
morning, with gusts up to 40 kt over the outer waters. Will leave
the current gale warning for the outer waters as is, but latest
guidance suggests gusts may fall below gale criteria in PZZ270
around 00Z Mon. Will let the gale for PZZ250 expire at 04Z and
replace with small craft advisories. Will need to closely monitor
this zone late tonight through Sun morning as the 00Z GFS is
hinting at 35 kt boundary layer wind speeds sneaking into that
zone between 12Z and 18Z Sun. The NAM is a little weaker with its
wind speeds.

There are some model differences regarding the location and track
of the surface low. The NAM and ECMWF shift the low center
inland into SW Washington 18Z Sun while the GFS keeps the low
center near Cape Disappointment. In any event, wind speeds will
begin to diminish late Sunday afternoon through the night, with
the strongest gusts holding out across PZZ275 the longest. Wind
speeds fall below 15 kt by Mon.

Seas have risen to 16 to 18 ft, pretty close to the ENP guidance.
The latest run has a core of 29 ft seas about 150 nm west of Cape
Disappointment 18Z Sun. Made minimal changes to the wave forecast
through Sun night. Expect the highest seas late Sun morning
through mid-afternoon. Wave heights diminish quickly from north
to south Sun night through Mon and expect seas to be under 10 ft
by 00Z Tue. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from midnight tonight to 5 AM PST
     Monday for Upper Hood River Valley.

     Winter Weather Advisory from 2 AM Sunday to 5 AM PST Monday for
     Central Columbia River Gorge-Western Columbia River Gorge.

     Winter Weather Advisory until 4 AM PST Monday for Cascade
     Foothills in Lane County-Northern Oregon Cascade Foothills.

     Winter Storm Warning until 5 AM PST Monday for Cascades in Lane
     County-Northern Oregon Cascades.

     Winter Weather Advisory from 2 AM Sunday to midnight PST Sunday
     night for Greater Portland Metro Area.

     Winter Weather Advisory from 2 AM to 10 PM PST Sunday for Lower
     Columbia-North Oregon Coast.

     Winter Weather Advisory from midnight tonight to 4 AM PST
     Monday for Central Coast Range of Western Oregon-Coast
     Range of Northwest Oregon.

     Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday for
     Central Willamette Valley-South Willamette Valley.

WA...Winter Weather Advisory from 2 AM Sunday to 5 AM PST Monday for
     Central Columbia River Gorge-Western Columbia River Gorge.

     Winter Weather Advisory until 4 AM PST Monday for South
     Washington Cascade Foothills.

     Winter Weather Advisory from 2 AM Sunday to midnight PST Sunday
     night for Greater Vancouver Area.

     Winter Weather Advisory from 2 AM to 10 PM PST Sunday for I-5
     Corridor in Cowlitz County-South Washington Coast.

     Winter Weather Advisory from midnight tonight to 4 AM PST
     Monday for Willapa Hills.

     Winter Storm Warning until midnight PST Sunday night for South
     Washington Cascades.

PZ...Gale Warning until 10 PM PST Sunday for Waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 NM.

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

     Small Craft Advisory for winds until 10 PM PST Sunday for
     Coastal waters from Cape Shoalwater WA to Cascade Head OR
     out 10 NM.

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

     Small Craft Advisory for winds until 10 PM PST Sunday for
     Coastal waters from Cascade Head to Florence OR out 10 NM.

     Small Craft Advisory for hazardous seas until 10 AM PST Monday
     for Coastal waters from Cascade Head to Florence OR out 10
     NM.

&&
$$

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland

This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the CWA or forecast area.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.