Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251107
AFDPQR

Area Forecast Discussion
National Weather Service
305 AM PST Sun Feb 25 2018

.SYNOPSIS...Rain and mountain snow will spread across the region this
morning as a strong cold front arrives. Showers later this afternoon,
with colder air spreading inland tonight. Lingering showers on
Monday, with snow levels rather low. But not much in way of
accumulations. Break in the weather Mon night, then the cool wet
weather resumes on Tue.
&&

.SHORT TERM...Today through Tuesday...Precipitation with next front
now spreading into western Washington and far northwest Oregon. This
in response to rather vigorous low that is digging southeastward
along the British Columbia coast. The cold front will push onshore by
late morning, then moves across the region and over the Cascades this
afternoon.

Decent shot of precipitation with the front, and to some degree the
post frontal showers. Generally, 0.50 to 0.75 inch for the Coast
Range/Willapa Hills, and 0.70 to 1.25 inch for the Cascades. But,
less for the interior lowlands, with 0.25 to 0.50 inch expected. This
mainly because the interior lowlands will experience another round of
rainshadowing off the coast mtns, such that showers will be less
intense/less in coverage later today into tonight.

Snow levels over the area sitting at 1500 to 2000 feet over the
Cascades, and 2000 to 2500 feet over the coastal areas. So while not
a lot of snow is expected on the coastal mountains, will see
significant snow in the Cascades, and to some degree, the foothills.
Will maintain the current Winter Storm Warning for the Cascades,
where will have gusty west to southwesterly winds today into the
evening, along with total snow accumulations of 15 to 30 inches
during that time. Foothills will be tricky, today into the evening,
as snow levels stay around 1500 to 2000 ft while the heaviest
precipitation is occurring, with the heavier precip over south
Washington at the optimal time. But, think snow levels tad too high
over the Oregon foothills, so will keep snow accumulations just below
advisory levels. By time snow levels lower to 1500 feet, the
precipitation will be waning.

Colder air will shift inland again tonight, with snow levels dropping
back down to 500 to 1000 feet. While precipitation is waning, is not
out of question to see mix of rain/snow showers again late tonight
into Mon am. But, think that areas below 500 to 800 feet will see
little if any accumulations. That said, will have to deal with
potential of icy spots on roads as temperatures drop into the lower
30s tonight, and even 20s closer to the Cascades foothills and Coast
Range/Willapa Hills.

Decreasing showers on Monday, as will see mix of sunshine and clouds.
Generally, best threat of showers will stay over the higher terrain.
Still expecting showers to end early Mon evening over most areas.
Cold and dry under partly cloudy skies Mon night, as region will be
between weather systems.

Next front will spread light rain across the region on Tue am. This
will not be all that strong, with 0.10 to 0.25 inch of rain. Snow
levels stay low at 1000 to 1500 feet. with several inches of new snow
for the higher terrain.                  Rockey.


.LONG TERM...Tuesday night through Saturday. A rather active weather
pattern looks to continue through the long term forecast period with
a longwave trough remaining across the western portion of the U.S.
through the period. Outside of the broad pattern, however, specific
details remain uncertain given large spread in the model guidance.
While the 12z GFS depicts a rather deep low pressure system just off
the Oregon/Washington coasts by Wednesday evening, there is
considerable spread in NAEFS members. It should be noted that the
ECMWF does show a somewhat similar low developing but with much less
impressive structure. Therefore, will maintain the forecast along a
compromise solution. Eventually, the large upper level trough
becomes more solidly centered over the far NE Pacific by late
Thursday. This would maintain an unseasonably cool air mass over the
region with snow levels again lowering to around 1000 feet. Will
need to continue to monitor the potential for some snow at least
mixing in below 1000 feet early next weekend as the cold air mass
looks to remain in place with at least enough moisture to support
showers. At this point, however, expect that the extended period
will feature continued enhancement of the Cascade snowpack but not
any additional low elevation snowfall. Cullen
&&

.AVIATION...Rain will spread into the area this morning with
MVFR spreading from the coast to the interior. Widespread MVFR
or worse through the morning, followed by increasing VFR for the
interior valleys Sun afternoon. Strong mid-level westerly winds
will keep mountain obscured through at least this evening, with
improving conditions tonight and Monday as precipitation wanes.

PDX AND APPROACHES...Expect MVFR cigs to develop by 15Z and last
through 20Z or so. There may be some rainshadowing beginning 20Z
with the increase in west to west-southwest winds coming off the
coastal mountains. This may be enough to bring low VFR or more
VFR than MVFR conditions. Southerly winds gusting 20-25 kt,
weakening some and becoming more westerly around midday. /mh

&&

.MARINE...A cold front will sag across the waters from northwest
to southeast today. This will bring solid Small Craft
Advisory winds with gusts 30-34 kt at times. Does not appear gale
will occur for PZZ270 as previously expected. Westerly winds
gusting 25-30 kt will continue tonight, but the nearshore zones
will subside late this evening. Higher pressure strengthens
Monday and Tue, but is interrupted by weakening low pressure
transiting the WA waters Monday and Tuesday mornings.

Forecast confidence improving with regards to Wednesday through
the end of the week. The 00Z GFS and ECMWF are in better
agreement than a few model runs ago, at least for now. Part of
the variance in forecast models is how they are handling the
cut-off low northwest of Hawaii. One trend is the GFS solution is
trending toward the ECMWF forecast with a 980-985 mb low near
Vancouver Island, B.C. by Wednesday afternoon. So for now have
trended the forecast more toward the ECMWF.

Seas in the low teens early this morning will build to the mid
and upper teens late today into Monday as the fetch remains
directed at WA & OR. Latest ENP guidance shows seas falling just
under 10 ft Tue morning. The latest ENP model develops a core of
30 ft seas off the South Oregon coast 12Z Thu, in response to the
deep low pressure as seen in the GFS. The ECMWF model has 12 to
15 ft seas over the waters 12Z Thu and is the favored solution.
/mh Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning for...
 North Oregon Cascades until 10 pm today
 Lane County Cascades until 10 pm today.

WA...Winter Weather Advisory for...
 South Wash Cascades Foothills until 4 pm today.

     Winter Storm Warning for...
 South Washington Cascades until 7 pm today.

PZ...Small Craft Advisory for winds until 10 PM PST this evening for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 NM.

     Small Craft Advisory for hazardous seas until 6 AM PST Tuesday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 NM.

     Small Craft Advisory for winds until 3 AM PST Monday for Waters
     from Cape Shoalwater WA to Florence OR from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 6 AM
     PST Monday.

&&
$$

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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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