Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 191804
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1004 AM PST Mon Feb 19 2018

.SYNOPSIS...Cool weather stays over the region for this week under
a northerly flow aloft. Occasional snow flurries will move over the
region this morning with no additional snow accumulations expected.
Another low elevation snow event is expected Tuesday and especially
Tuesday night as a couple of upper shortwave troughs move south
across the region. A couple more shortwaves late in the week bring
more chances for rain and mountain snow.

&&

.SHORT TERM...Today through Wednesday...Cloud cover overnight limited
radiation cooling and the morning temperatures weer a bit warmer than
forecasted. The temperatures this morning are still near or just
below freezing, keeping any snow that fell last night on the ground.
Snow flurries have been observed across the area from the coast to the
Cascade foothills this morning, and radar imagery is showing light
reflectivities moving north to south over the area. These snow
flurries will be brief, spotty, and not generate any new snow
accumulations. The snow flurries will end later this morning or early
this afternoon.

Tonight will be dry and cool. More clearing this evening and tonight
will provide better conditions for radiation cooling and expect
temperatures will dip down to the teens for the Cascade foothills,
the low to mid 20s for the interior valleys, and the upper 20s to low
30s for the coast early Tuesday.

The dry and cold conditions will prime the environment for another
potential low-elevation snow event later Tuesday as a low drops north
to south just offshore the Washington and Oregon coast. The 06z and
12z models are trending towards a moister forecast, and have
increased pops and qpf for Tuesday afternoon and night with the
morning update. This means there is a higher probability for low
elevation snow and the potential for higher snow accumulations.

The models are fairly consistent in showing a baroclinic band set up
across NW Oregon late Tuesday afternoon, but vary on where it will
set up. The Nam and the ECMWF forecasts the band will set up along
the WA/OR border near the Portland metro area, where as the GFS has
it over the Central Willamette Valley (near Salem). Models have
historically struggled with forecasting the location and speed of
progression of these type of weather systems through our area, and
usually forecast too little QPF and move it too quickly. Therefore
the forecast confidence on the location and amount of the snow will
be low, although the odds for low-elevation snow (with decent
amounts) are high. ~TJ

.LONG TERM...No Changes. Previous discussion follows...Wednesday
night through Sunday...The large-scale pattern remains rather
consistent across the western U.S. for the second half of this week,
as a high amplitude ridge remains over the Pacific centered
near/around 140W with a deep trough in place over the western CONUS.
This will maintain generally northerly flow over the region, with a
series of shortwave impulses  moving through the region. These
impulses will be focus points for additional chances of rain/snow
through 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. Maintained some mention of PoPs late Wednesday
and Thursday, but at this point expect the snow level to remain
around 1,500 feet or so through this time period.  While the ECMWF
has some additional moisture compared with the GFS, at least half of
the GEFS members are more favorable for precipitation so have trended
this way. The next strong system could arrive around the weekend and
depending on the degree of cold air, there will be some potential for
snow down to the higher hills once again, depending on how much cold
air is in space. Nonetheless, below normal temperatures and only
occasional infusion of moisture can be expected through the week.
Cullen
&&

.AVIATION...Skies will clear from north to south today as low
pressure drops further south of the region and dry northerly
flow strengthens. Cigs of 2500-3500 that are lingering in the
interior lowlands south of KSLE should scatter out between 18Z-
20Z. VFR conditions should prevail this afternoon and most of
tonight. Another low pressure system will be approaching from the
north later tonight, then move through the offshore waters
tomorrow. Cigs will increase overnight, with light snow spreading
onto the coast after 12Z. The coast may see MVFR conditions
develop between 12Z-18Z, and some light snow accumulations are
possible. Flurries may develop over the interior lowlands as
well, but no accumulation is expected. Think conditions will
remain VFR through Tue morning for the interior.

PDX AND APPROACHES...VFR today through tonight with clearing
skies. High clouds will increase overnight, with cigs lowering to
around 5 kft by Tue morning. Snow flurries possible between
12Z-18Z Tue, but little to no accumulation is expected. Pyle

&&

.MARINE...Wind speeds continue to slowly ease this morning. Only
the outer zones PZZ270 & 275 remain above 25 kt. Winds will ease
through the day then should be backing to the S-SW late tonight
and Tue. Models are in good agreement that another low will
approach the waters tonight and move through the offshore waters
Tue. It appears that there may be a period of 20 to 25 kt wind
gusts over the near shore waters with 20 nm of the coast during
the day Tue.

Models show another low pressure system moving north to south
near the waters late Wed into Thu, with a period of low end small
craft advisory winds over the outer waters.

Seas remain in the 11 to 14 ft range this morning. They will
continue to slowly subside through the day, dropping below 10 ft
later this afternoon or this evening. Seas then look to remain
below 10 ft through the rest of the week. Pyle


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until noon PST today for Waters
     from Cape Shoalwater WA to Florence OR from 10 to 60 NM.

     Small Craft Advisory for hazardous seas until 7 PM PST this
     evening for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

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

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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.



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