Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 062004
Area Forecast Discussion
National Weather Service Portland Oregon
1203 PM PST Tue Dec 6 2016
.SYNOPSIS...Clouds and showers will be decreasing from the north
today as drier northerly flow spreads in and the system from MOnday
moves south. An upper ridge will build in tonight and Wednesday for
drying, with increasing offshore winds on Wednesday. A strong winter
storm will begin to spread in from the south and impact the area
Thursday with a mix of snow and sleet changing to freezing rain and
sleet and eventually to rain from south to north over mainly the
inland areas through the entire day of Thursday. The coast may see a
mix of rain and snow before changing to rain. Strong east winds
through the Gorge and south to southeast winds along the coast are
expected. Most places will be rain Thursday night and rain showers
Friday except mixed precipitation will continue in the Gorge into
Friday. More typical unsettled weather will continue through the
weekend and into early next week.
.SHORT TERM...Today through Thursday...Weather is slowly improving
from north to south today with decreasing clouds and showers. Low
clouds in the valley may take a while to break up today especially
south of Portland.
An upper ridge will build in tonight and Wednesday for dry weather.
Expect areas of valley freezing fog and low clouds to redevelop
tonight and Wednesday morning. A light easterly gradient will develop
in the Gorge later tonight, then increase on Wednesday with most
places seeing some wind Wednesday. Tonight will be cold in the wake
of the Monday system, and Wednesday will continue cold and somewhat
bitter feeling from the effects of the wind.
Attention then turns to the very significant winter storm for later
Wednesday night and Thursday, the strongest winter storm of this sort
we have had in quite a while. Look for precipitation to slowly lift
north through the area Wednesday night, probably just approaching the
Portland area around 4 am, then spreading north Thursday morning.
Look for a brief period of an inch or two of snow or sleet in the
inland areas from about Salem south late Wednesday night before
changing to freezing rain and sleet Thursday morning and rain late
Thursday morning and afternoon. Farther north in the inland areas
around Portland northward look for 1 to 3 or 2 to 4 inches of snow in
the morning before changing over to sleet then freezing rain in the
afternoon with up to about a quarter inch of ice possible. The
Portland area north should change to rain in the evening. The Gorge
and Upper Hood River Valley will see several inches of snow Thursday,
with freezing rain and sleet moving in Thursday night, possibly
lingering into Friday. The Cascades will mainly see some snow with
some rain below the rising snow levels.
The models are showing a decent low moving up the coast Thursday into
Thursday night that will bring strong east winds to the Columbia
River area, and southeast to south winds along the coast.
Bottom line is that Thursday for much of the area weather is going to
cause a lot of problems. Tolleson
.LONG TERM...No Changes. Beyond Thursday, the big story will be
continuing snow in the Cascades. Several more feet of snow are likely
for Thu night through Sunday, with snow levels generally hovering
between 2000 and 3000 feet. Snow may even impact a few of the Coast
Range passes as snow levels dip to near 1500 feet at times.
.AVIATION...Weak low pres moving south just off the coast this
morning is bringing some light showers for areas south of a Salem
to Lincoln City line. Mix of MVFR and IFR conditions this morning
improve to VFR this afternoon. The trend will be toward clear
skies this evening. This may allow IFR freezing fog to form tonight
into Wed AM. Developing offshore flow should prevent fog from
forming in areas adjacent to the gorge and at the coast.
KPDX AND APPROACHES...Expect low MVFR or IFR cigs to remain
through the morning hours. Conditions improve to VFR this
afternoon, with skies clearing this evening. Expect light
offshore flow to prevent any fog formation overnight into Wed.
.MARINE...Expect winds to remain fairly light through Wed
morning but could see a couple of gusts above 20 kt this morning.
Then we will see a strong offshore flow pattern set up later Wed
into early Thu. Expect that we will see some gale force easterly
winds over the outer waters during this time. A strong frontal
system will then approach Thu. There is some disagreement on
exactly what track this system will take, but it appears likely
that we will see a period of gale force southerly winds at some
point Thu. Expect winds to remain gusty out of the west Fri on the
back side of the low, but confidence is not high on the details at
The westerly swell train that has been impacting the waters for
the past several days will finally subside today. Expect seas to
remain around 10 to 12 ft into this afternoon, then drop below 10
ft during the late afternoon. The late week frontal system
should push seas at least back into the mid teens, with the
potential for 20 ft seas or higher depending on the track of the
low and how strong the winds end up being. Bowen/Pyle
PZ...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.
Small Craft Advisory for Rough Columbia River Bar until 11 AM
PST this morning.
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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.