Area Forecast Discussion
Issued by NWS Portland, OR

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319
FXUS66 KPQR 190430
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
828 PM PST Sun Feb 18 2018

.SYNOPSIS...Cool weather stays over the region for this week. Showers
decreasing tonight, then dry Mon into Tue. But, will see renewed
chance of rain and low elevation snow for later Tue, which likely
continues through end of the week.

&&

.SHORT TERM...Tonight through Wednesday...Satelitte imagery shows a
surface low moving over the western Columbia River Gorge this
evening. A decent band of showers moving around the low are impacting
the South Washington Cascade foothills and the Portland/Vancouver
metro area.  Temperatures are cooling quickly as colder air moves in
from the north, and the showers are either mixed with snow or all
snow with localized areas seeing bursts of half to an inch of snow.
These showers are making its way south and will move over the Oregon
foothills and the higher elevations of the Central Willamette Valley.
Another band of showers ahead of this one is moving over the Oregon
Cascades with the tail end providing mixed precipitation for the
south Willamette Valley. THe low will move east of the Cascades by
midnight ending the threat for snow showers for the Portland Forecast
Area.

Drier and colder air will move in from the north behind the low. The
beginning edge of this colder air is starting to filter into SW
Washington and NW Oregon this evening as dew point temperatures have
already lowered into the 20s for Kelso and Scapoose. Widespread sub
freezing temepratures are expected tonight into Monday morning which
will likely lead to icy roads. ~TJ

From previous discussion last sent at 333 PM...Should remain chilly
despite more sunshine on Monday. Likely to see highs stay in the mid
to upper 30s over the lowlands, with 20s in the mountains. The next
shortwave in the northerly flow aloft is expected to drop down Tue,
but with models showing most of the energy focused offshore. Some
models suggesting mid level moisture able to spread inland with this
system. Will add in some low pops for light snow Tue, with the best
chances along the coast, but of course this still infers that dry
weather remains the more likely outcome for Tue.

Models still having problems on how to resolve Wed pattern. ECMWF
indicates better threat of precipitation over the region as another
disturbance drops into the Pac NW. GFS and NAM showing system either
staying too far north, or just offshore. If so, would wind up see
minimal threat of precipitation over the region. With confidence not
all that great, will trend with a compromise and keep PoPs in chance
range for Wed. Snow levels will still be low, generally 500 to 1000
feet. Good bet that any precipitation may result in light snow, but
accumulations light at this time.             Davis

.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...Surface low near K4S2 at 04Z. Drier air generally
north of a KTMK to KSPB line resulting in VFR conditions. Areas
south of the line remain in wrap-around moisture with generally
MVFR or worse conditions. Some minor snow accumulations are
possible in SW Washington east of Interstate 5 south through the
Central Willamette Valley and Cascade foothills through at least
07Z. Expect gradual improvement from north to south overnight.
However, some of the central and south valleys may hang on to
MVFR or IFR cigs into Mon morning.

PDX AND APPROACHES...Wrap-around moisture centered over Clark
County and the terminal, resulting in IFR to low-end MVFR
conditions. The terminal may pick up an inch or less snow
accumulation before the organized cluster of showers weakens and
moves away. Precip ends overnight with freezing temperatures.
Temperatures to warm above freezing around 20Z Mon. Weishaar

&&

.MARINE...Wind speeds continue to slowly ease this evening. Will
end the gale warning for PZZ270 and replace with a small craft
advisory for wind. Will hold on to the gale for PZZ275, although
the gale gusts will be more confined to the southwest quadrant.
Wind speeds expected to fall below 15 kt across the entire marine
area by Mon afternoon. North wind will shift to south late Mon
night and Tue morning, but remain below 15 kt.

Seas continue to slowly moderate, but were still around 20 ft at
the buoys as of 03Z. ENP guidance indicates seas falling to near
10 ft across the S Washington waters by 12Z, but still in the
upper teens across the far south parts of PZZ255 and PZZ275.
Seas fall even more Mon, dropping below 10 ft by Mon evening.
Models show a low pressure system moving north to south near the
waters Wednesday, but there are major differences between the
models as to the impacts of the low due to strength and track.
Right now it doesn`t look very impactful, but another system
Thursday may increase winds and seas again. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening for
     Central Coast Range of Western Oregon-Central Columbia
     River Gorge-Upper Hood River Valley-Western Columbia River
     Gorge.

     Winter Weather Advisory until midnight PST tonight for Cascade
     Foothills in Lane County-Cascades in Lane County-Northern
     Oregon Cascade Foothills-Northern Oregon Cascades.

WA...Winter Weather Advisory until 10 PM PST this evening for
     Central Columbia River Gorge-Western Columbia River Gorge.

PZ...Small Craft Advisory for winds until noon PST Monday for Waters
     from Cape Shoalwater WA to Cascade Head OR from 10 to 60
     NM.

     Gale Warning until 6 AM PST Monday for Waters from Cascade Head
     to Florence OR from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 7 PM
     PST Monday.

     Small Craft Advisory for hazardous seas until 4 PM PST Monday
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 NM.

     Small Craft Advisory for winds until 1 AM PST Monday for
     Coastal waters from Cascade Head to Florence OR out 10 NM.

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

&&
$$

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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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