Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 101113
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
312 AM PST Mon Dec 10 2018

.SYNOPSIS...Showers will be mostly over the higher terrain today and
gradually decrease. Temperatures in the Gorge and Hood River Valley
will slowly moderate, and likely rise above freezing late this
morning. A warmer and wetter frontal system will bring additional
rain and mountain snow on Tuesday. The next front stalls over
Washington Wednesday and Thursday keeping most of NW Oregon dry. SW
Washington may see a prolonged wet period though with this
stationary front. The front will finally move inland and across NW
Oregon on Friday. Wet weather is expected to continue for the weekend
and into next week.

&&

.SHORT TERM...Today through Thursday...Post-frontal showers will
decrease today. The east winds have been stubborn through the Gorge,
and the temperatures in the Hood River Valley and Central Columbia
Gorge are still below freezing. Radar shows the showers are more
orographic, and expect them to be less frequent in the valleys and
lower elevations than for the higher terrain. Any showers that make
it to the central Gorge and Upper Hood River Valley this morning will
likely be in the form of freezing rain, but accumulations will be
very light. Snow accumulations in the Cascades will be light too
(less than 2 inches).  Due to the decrease in snow and ice
accumulations and that the showers will be diminishing throughout the
day, have decided to end the Winter Weather Advisories.

Showers will end late this afternoon, but rain and Cascade snow with
the next front is expected to arrive overnight tonight. This front is
stronger, wetter, and milder (temperature), and has the potential to
produce 2 to 3 inches of rain for the coast, coastal mountains, and
the Cascade Foothills Tuesday morning through Tuesday night.  Snow
levels in the Cascades will initially be around 2500 feet, and expect
3 to 6 inches of new snow Tuesday morning before the snow levels rise
above the Cascade passes Tuesday afternoon. The snow levels lower
below the passes behind the front Tuesday night as an upper trough
continues showers. The showers will be mainly confined to the higher
terrain Wednesday morning, and end around noon.

A warm front will likely generate rain across extreme SW Washington
Wednesday evening through Thursday night as it stalls just north of
the Portland forecast area. NW Oregon may not see any rain with this
front and get a brief dry period. ~TJ

.LONG TERM...No Changes. Previous discussion follows...Thursday
night through Sunday...A surface low riding up a stationary front
from the southwest will move the front eastward across NW Oregon on
Friday. There will be a decent amount of rain with this system, but
it probably won`t be as wet as the system on Tuesday, due to it
moving through fairly quickly.

Post frontal showers continue into Saturday, with snow levels
dropping to 2500 feet. We could see a decent amount of snow in the
Cascades with the showers behind the front Friday night into early
Saturday. Some uncertainty in timing of the progression next
weekend, but we should see a break between systems sometime Saturday
afternoon/evening. Another system will bring widespread rain late
Saturday night through Sunday. -McCoy/TJ

&&

.AVIATION...Onshore flow with orographically enhanced showers
will subside through the day. With the moist air mass in place
and little mixing, widespread IFR cigs and vis have developed.
Latest GFS, GFS-LAMP MOS guidance handles the current situation
well and holds on to IFR conditions through midday or so then
trends to VFR after that. Mountains and higher terrain
frequently obscured through Mon morning. Next system brings rain
to the coast late this evening with gusty southerly winds
beginning Tue morning.

PDX AND APPROACHES...IFR cigs at KPDX with reduced visibility in
fog in the surrounding area, especially in the Tualatin Valley.
Expect improvement to VFR Mon afternoon. /mh

&&

.MARINE...Another gale event expected for most waters later
tonight into Tue. Some concern that models have winds that are
too strong. With the last system, models indicated gusts around
40 kt just ahead and with the front. But best observed was 35 kt
gust. 00Z models are in general agreement so will go with a gale
warning for PZZ250,270,275. Gales may reach PZZ255 briefly Tue
afternoon. Conditions settle down Tue night through Wed, but
models show low-end gales developing again late Wed and Wed
night. Much larger model disparity appears Fri through the
weekend. Operational ECMWF and GFS show a rapidly-developing low
pressure area near 45N 135W 00Z Fri, but models differ on track
and strength. Went with a blended solution due to such large
model variance.

Seas forecast to hover in the 11 to 13 ft range through this
afternoon. Guidance shows seas in the mid to upper teens Tue
night through Wed night. Model differences increase late in the
week and into the nearly next week due to the differences in the
intensity and track of the strong lows mentioned above. There is
reasonable confidence seas will be close to 20 ft next weekend
with the more extreme solutions showing seas closer to 25-30 ft.
Have gone closer to the WAM output for now, but would expect
trends to change this far out in time. /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning from 11 PM this evening to 4 PM PST Tuesday for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 NM.

     Small Craft Advisory for hazardous seas until 4 PM PST this
     afternoon for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

     Gale Warning from 4 AM to 4 PM PST Tuesday for Coastal waters
     from Cape Shoalwater WA to Cascade Head OR out 10 NM.

     Small Craft Advisory for winds from 4 AM to 4 PM PST Tuesday
     for Coastal waters from Cascade Head to Florence OR out 10
     NM.

     Small Craft Advisory for hazardous seas from 4 AM Tuesday to 6
     AM PST Wednesday for Coastal waters from Cascade Head to
     Florence OR out 10 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 forecast area.


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