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Area forecast discussion 
National Weather Service Portland or
220 am PST Sat Jan 31 2015

Synopsis...an upper ridge and offshore flow will remain over SW
Washington and northwest Oregon today. The ridge shifts east Saturday
night as a frontal system approaches the coast. The front moves
across the area Sunday. A stronger system is expected to impact the
region late Sunday night and Monday. A series of wetter cold fronts
is likely late next week into next weekend. Significant snows at
Cascade Pass level appear unlikely during the next week.
&&

Short term...today through Monday...persistence looks like the way to
go today. Satellite fog imagery as of 0930z showed considerable fog
in the south Willamette Valley and lower Columbia around kkls...with
lesser amounts in the central and north Willamette Valley. This
pattern appears to be similar to 24 hours ago. Kttd-kdls gradient was a
meager -2.3 mb at 10z...pretty close to the 3-hour forecast off the 06z
NAM. The NAM does increase the gradient this afternoon to -5 to -6 mb
by 21z. Model 850 mb temperatures do not show any appreciable change today
compared to Friday so went close to persistence temperatures for most areas.
NAM maintains solid stratus in The Gorge to around kczk. NAM
cross-section from kast through the Columbia Gorge shows increasing
high-level moisture after 03z sun. This may have an impact on fog
formation...but suspect the central and south Willamette Valley will
see the fog return.

Models continue to advertise a change in the overall pattern
beginning Sunday. A frontal system reaches the coast late Sat night
then inland sun. Models seem to faster with this system compared to
earlier runs. Model quantitative precipitation forecast with this one not all that impressive.
Mountains not going to get much in the way of needed snowfall as snow
levels expected to be above 5k feet. A more impressive system impacts
the forecast area late Sun night and Monday. GFS is quite bullish on the
quantitative precipitation forecast...with a core of over an inch in 6 hours on the central Oregon
coast Monday morning. Went more with the European model (ecmwf) quantitative precipitation forecast amounts...with maybe
up to one-half inch in 6 hours for the coast Monday morning. Fairly decent
850 mb orographic flow into the Coast Range and Cascades 18z Monday
through 00z Tuesday. Unfortunately...as has been the case most of this
winter...snow levels will stay above the Cascade passes. Slightly
lower snow levels for the S Washington Cascades Monday with 1000-500 mb
thickness values near 540 dm...but snow levels likely to be a bit
lower due to some degree of east low-level flow. Weishaar

Long term...Monday night through Friday...in the wake of the system
that moves through Monday...the models develop a warm front and
attempt to eventually lift it north through the Pacific northwest in
the middle week period. Unfortunately...the models are having a tough
time settling on when and where it will form and how wet it will be.
It will likely form somewhere over southwest Oregon or extreme
northern California...then lift north around Wednesday. For now have
broad brushed the probability of precipitation a bit due to the timing and intensity
problems. The next rather mature and decently strong occluded front
comes in around Thursday...followed by a series of rather wet fronts
late next week into the weekend. The general trend next week is
toward a wetter more active pattern. At this point...other than a
couple of brief dips...snow levels remain rather high and these
systems will not likely add much if anything to the deficient snow
pack in the Cascades. Weishaar
&&

Aviation...widespread fog has developed over the southern
Willamette Valley which has brought ceilings and visible down to
LIFR/vlifr at keug. Ksle is VFR at the moment...but fog is
pushing northward and should bring ceilings and visible down to LIFR over
the next hour. Fog has also developed along the north or
coast...with a light east wind occasionally bringing ceilings and visible
up to MVFR until the wind calms again bringing ceilings and visible back
down to IFR/LIFR. Persistent east wind along the central Oregon
coast will keep konp VFR overnight. Patchy fog is developing over
the north Willamette Valley...with temperatures in some areas below
freezing. Light easterly winds are keeping the fog patchy...and
clear at kpdx and kttd...but fog again is coming eastward up the
Columbia River from Kelso and will move into kpdx similar to
yesterday.

Kpdx and approaches...VFR conditions will give way to IFR/LIFR ceilings
and visible by 12-13z as fog moves in from the northwest along the
Columbia River. Expect fog to persist through around 18z Saturday.
VFR conditions return Saturday afternoon as east winds begin to
increase at the terminal. -McCoy

&&

Marine...a change in the weather pattern is on the menu for this
weekend...with the first in a series of progressively stronger
frontal systems moving through Sunday morning. This first front on
Sunday brings the possibility of some Small Craft Advisory gusts
above 20 kts while bringing seas up to around 8 feet. The second
frontal system moves through on Monday...bringing solid Small
Craft Advisory winds with gusts 30 to 35 kts likely. Strong winds
will ramp up early Monday morning and persist through the day
until winds ease behind the front late Monday night or early
Tuesday. This system will also bring seas up to around 12 to 13
feet on Monday. Confidence is increasing for an even stronger system
Thursday or Friday which could generate southerly gales and bring
seas up to near 20 feet. -McCoy



&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...none.
&&

$$

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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.

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