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Area forecast discussion 
National Weather Service Portland or
923 PM PST Monday Nov 30 2015

Synopsis...lingering light rain associated with a decaying occluded
front will continue into this evening...with light freezing rain
possible in the Columbia River gorge and Upper Hood River Valley. A
more significant frontal system will move onshore late Tuesday into Wednesday
morning...bringing widespread precipitation to the region along with
potential for a period of significant freezing rain and sleet in
portions of the Columbia River gorge...Upper Hood River Valley...and
Cascades. A secondary low is expected to form along the stalled
frontal boundary...bringing more precipitation Wednesday and Wednesday night.
Expect a generally milder...wetter...and more progressive weather
pattern to then continue for the foreseeable future with additional
systems occurring every 24 to 36 hours.


Update...radar this evening shows scattered showers mostly inland
from Marion County Oregon north through Skamania County Washington.
Most lowland temperatures remain above freezing at 8 PM...but there
are pockets below 32 degrees which may be seeing freezing rain.
Precipitation is sticking around due to an upper trough currently swinging
through the area. Models show the trough moving east and showers
dissipating by around 08z...or midnight local time. With overcast
skies...expect temperatures will not budge much before that
do not expect widespread freezing rain or any wintry precipitation threat in
The Lowlands. Latest satellite imagery shows some clearing of skies
over the extreme southwestern corner of Oregon which will spread
northeast through the overnight hours. Clearing skies will help
temperatures finally drop below freezing...but likely not until late
tonight and after the precipitation stops. Current thinking is that there
will be enough time for drying before temperatures drop that freezing
of lingering surface moisture will not be a problem...but could see
some isolated slick spots during the Tuesday morning commute if
drying does not occur. Could also see some lowland fog Tuesday
morning. Overall the message for the Tuesday morning is that
commuters should allow themselves a few extra minutes to reach their
destinations due to any combination of possible slick patches on
roads and fog. Adjusted forecast to reflect latest radar trends and
to add slight chance of freezing rain with precipitation tonight. Also
changed fog to freezing fog Tuesday morning where temperatures will
be cold enough. Bowen

Short term (previous discussion)...tonight through Wednesday
morning...a dissipating occluded front associated with an upper low
moving north offshore has brought light precipitation to portions of
SW Washington and northwest Oregon today. With the chilly start to the
morning...precipitation fell as freezing rain or sleet for many in
the interior lowlands and along the east slopes of the Coast Range
earlier today. Precipitation totals were very light...on the order of
a trace to a couple of hundredths of a inch...and no significant
impacts from the ice have been reported. The front has pretty much
fallen apart at this point...but some additional areas of light rain
are showing up on radar over the past couple of hours and will likely
continue into this evening. With temperatures still below freezing in The
Gorge and in the Cascade foothills...will maintain a slight chance of
freezing rain tonight for these areas. There will be a relative lull
in the weather overnight and much of tomorrow. Based on satellite
trends...there may be some clearing in the cloud cover late
tonight...particularly over southern portions of the forecast
nudged overnight lows down a few degrees in some spots.

The next system will approach the Pacific northwest later Tuesday...and will bring
more widespread and significant precipitation to the region than we
saw with this past front. A fairly moist frontal boundary with
precipitable water values around 1 inch will begin to spread rain
onto the coast during the afternoon...then push inland during the
evening and overnight hours. For most of the not expect
this to be anything other than a fairly typical mild winter time
front. There will be some gusty winds along the beaches and coastal
headlands...where gusts of 40 to 50 miles per hour are possible late Tuesday and Tuesday
evening. The most significant impacts with this system are expected
near the Hood River Valley and Columbia River gorge. With cold air
still locked into the interior Pacific northwest east of the
appears likely that a good chunk of the precipitation will fall as a
wintry mix near Hood River...and in some sheltered low elevation
valleys in the S Washington and north Oregon Cascades. Forecast model
soundings from the 12z NAM suggest surface temperatures remain below
freezing near Hood River well into Wednesday afternoon. Soundings from the
12z uw WRF-GFS also indicate subfreezing temperatures near Hood River into
Wednesday am through the period of heaviest precipitation. Given that quantitative precipitation forecast
values are in the range of 0.5 inch or so during this
appears that there is potential for a significant freezing rain or
sleet event. Decided to issue a Winter Storm Watch for freezing rain
from Tuesday night through Wednesday afternoon...highlighting potential for
0.25 or greater ice accumulations through Wednesday. Pyle

Long term (previous discussion)...Wednesday through Sunday...a low
moving along the baroclinic zone will likely bring another front and
burst of precipitation across the region Wednesday and Wednesday
night. East winds will continue through Thursday and a shallow layer
of cold air may persist for The Gorge near Hood River...the Upper
Hood River Valley...and some of the sheltered valleys in the S
Washington and north Oregon Cascades. These areas will be prone for
additional freezing rain with this system. Models forecast that the
near surface temperatures will rise above freezing Wednesday
evening...and the precipitation type will convert to rain. Have
leaned towards this solution for the Wednesday night and Thursday
forecast...but the forecast confidence is low since the models tend
to warm low-level temperatures during east wind events too quickly.

The snow levels will rise to around 7000 feet Wednesday...and do not
anticipate any additional winter weather concerns with the Wednesday
front. Showers behind the front Wednesday night will
gradually decrease through Thursday morning. More precipitation is
expected Thursday night and Friday as the upper trough moves over
the area...with snow levels lowering to below pass elevations.
Decreasing showers Friday afternoon and night before another moist
front brings additional rain and mountain snow next weekend. Tj


Aviation...06z taf package expectations. Light mainly rain
showers continue ksle-konp northward...with temperatures very
close to freezing. However all Willamette Valley and coastal
terminals remain slightly warmer than freezing and runway icing
problems are not anticipated as -shra tapers off. Kczk and Hood
River Airport remain a much different story...with temperatures below
freezing and occasional -fzra/-pl/-sn possible for the rest of the

As for cigs/vsbys...generally VFR this evening with ceilings around
030-040. Ceilings are expected to lower slightly overnight... with
MVFR likely most terminals by 12z...except near the Columbia Gorge
and coast where easterly winds should keep the low levels too dry
for low ceilings to develop. Some local IFR is possible around
kcvo/keug as winds remain light and dewpoints are higher. Where
low clouds develop they should be stubborn to lift/clear
Tuesday...likely not doing so until 20z or possibly later. With
low stratus sticking not anticipate widespread fog
issues tonight.

The konp AWOS remains we are still not receiving
observations. We will continue to issue tafs for that site...but
amendments are not likely without surface observations.

Kpdx and approaches...E-se winds around 10 knots will continue
tonight...but are expected to increase to 10-15 knots with gusts to
25 knots as the next frontal system pulls more wind through the
Columbia Gorge Tuesday afternoon. The easterly flow will probably
keep ceilings above 030 with VFR visibilities. A few -shra remain possible
until 08z...but temperatures should remain above freezing. Temperatures may fall
to 31-32 degree f after 12z...but any precipitation from earlier this
evening will likely have evaporated off the runways by then.

&& pattern expected for the coastal waters with
gales at times as a series of lows/fronts move through. For
tonight...S-SW winds are gusting to around 30 knots with seas 13-16
feet. There may be slight easing later tonight as todays low
pressure system moves into British Columbia and brief upper level
ridging moves across the Pacific northwest waters. However any respite will
be very brief...therefore Small Craft Advisory for winds/seas remains in effect
until the Gale Warning for the next system begins Tuesday morning.
That system...presently nearing 40n/130w...will brush the coast
with gusts 35-40 knots by midday. This will be followed up quickly by
a stronger system right on its heels near 140w. Isobars will
remain parallel to the coast...which should keep the strongest
winds in the offshore waters. However it is not out of the
question that a brief coastal jet could bring a few low-end storm
force gusts as the stronger system moves through Tuesday evening.

A stalled frontal zone will keep the storm track near the coastal
waters as more...and possibly stronger...low pressure systems develop
along it Wed-Thu. 00z NAM/GFS develop a sub-990 mb low near the
Oregon coast...which would almost certainly bring storm force
winds to the waters Thursday/Thursday night as it lifts northward along or
near the coast. 12z European model (ecmwf) remains more conservative with this
system...but nonetheless predicts a volatile period in our coastal
waters through at least Thursday. The details will likely become
clearer over the coming days...but the bottom line is that strong
winds and seas approaching 20 feet...or higher...are likely through
at least Thursday. Long range forecast models suggest additional active
weather this upcoming weekend. Mariners should pay close attention
to the weather forecast the next several days.Weagle


Pqr watches/warnings/advisories...
or...Winter Storm Watch from Tuesday evening through Wednesday
afternoon for central Columbia River gorge-northern Oregon
Cascades-Upper Hood River Valley-western Columbia River

Washington...Winter Storm Watch from Tuesday evening through Wednesday
afternoon for central Columbia River gorge-South Washington
Cascades-western Columbia River gorge.

Pz...Small Craft Advisory for winds until 7 am PST Tuesday for
coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Gale Warning from 7 am Tuesday to 3 am PST Wednesday for
coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Small Craft Advisory for hazardous seas until 7 am PST
Tuesday for coastal waters from Cape Shoalwater Washington to
Florence or out 60 nm.

Small Craft Advisory for rough Columbia River bar until
1 am PST Wednesday.



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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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