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fxus66 kpqr 101839 

Area forecast discussion
National Weather Service Portland Oregon
1039 am PST Sat Dec 10 2016

Synopsis...winds are expected to turn west in the Columbia Gorge
late today, finally bringing an end to the low elevation snow and
freezing rain. A series of low pressure systems will maintain showery
weather into next week...with temperatures remaining near or below
normal. Snow levels will dip down to the Coast Range and Cascade
foothills at times. Much colder weather will return beginning mid
week with the possibility of low elevation snow amounting to a
couple inches, but this remains very uncertain and no large snow
fall is currently expected.


Short term...isolated to scattered showers continue across the
region this morning with quantitative precipitation forecast generally less than 0.10 inch. A
Troutdale to dalles easterly surface pressure gradient continues to
support below freezing temperatures for the Upper Hood River
Valley...the Columbia River gorge...and Portland Metro area. There
will be intermittent freezing rain for these areas this morning, but
do not expect additional ice accumulations on most Road surfaces with
the showers this morning. The ice is still thick on many surfaces
like trees and power lines, and will continue to pose hazards as the
ice gradually melts today. Trees may topple over or ice fall from
high surfaces.

When will the temperatures warm above freezing for the Portland Metro
area and the Columbia River gorge? That is the main short term
forecast challenge of the day. Models always scour out the cold air
for east wind events too quickly, and are only slightly helpful for
this forecast challenge. Warming will begin when the east winds
through The Gorge are replaced by west or southwest winds, and it
appears the best chance for that will be late this afternoon or early
this evening. Temperatures will gradually warm late this morning and
early this afternoon. The Portland Metro area should warm above
freezing between noon and 3 PM, with The Gorge and Hood River area
warming above freezing between 2 and 5 PM.

Water vapor imagery shows a series of upper level shortwaves
approaching the Pacific northwest and visible imagery shows a wide
area of open-celled cumulus over the NE Pacific. These waves will
send a series of fast moving fronts across the area, and satellite
imagery shows the first of these boundaries currently reaching the
southwest Washington coast. There has been a couple of lightning
strikes embedded within the showers near the coast and have added
isolated thunderstorms to the coastal waters of South Washington and
north Oregon.

Showers will increase across the area this afternoon and evening and
continue Sunday as the next shortwave trough moves over the area.
Snow levels will be between 2500 and 3000 feet. The Cascades will get
another 5 to 10 inches of snow with these showers and have issued a
Winter Weather Advisory from late this afternoon through Sunday
afternoon. Snow will likely continue to impact travel over the
Cascade passes. Showers will continue Sunday night and Monday but
with lighter rain and snow accumulations. Tj

From previous discussion...Monday night will bring a closed low
diving well offshore which allows brief upper ridging to appear over
the area. Tuesday is shaping up to be dry across the area. Am still
maintaining some low end pops from Salem southward as warm frontal
rain will edge northward from California. /Jbonk

Long changes. Previous discussion follows...Monday night
through Friday. There will be a chance of showers with valley rain
and mountain snow to start the period as an upper level trough of low
pressure slips southward into northern calif. On tues, a fairly
strong ridge of high pressure begins to move southward from Canada
into eastern Washington with an accompanying cold air mass. This
setup will bring offshore flow to the region for the middle and
latter part of the week. Nwp models indicate there will be a fairly
dry period during the middle part of the week. A fairly strong
east-west pressure gradient sets up the latter part of the week
brining some strong easterly winds through The Gorge by weeks end. Tw


Aviation...slow change today for Interior Valley areas north of
about ksle. Generally IFR in the Willamette Valley and inland
valleys of SW Washington as of 1630z. VFR along the coast and in
the central and south Willamette Valley. Cold air remains trapped
in the north this morning. However, a frontal passage this
afternoon should erode the last of the cold air. Expect primarily
MVFR conditions this afternoon through 12z sun with higher
terrain obscured. IFR conditions from ksle to kkls will improve to
at least MVFR this afternoon with the front.

Kpdx and approaches...IFR at the terminal and vicinity at 1630z.
Have received a few pireps noting tops 012-015. IFR to persist
through early afternoon. Conditions expected to improve to at
least MVFR after 20z with a frontal passage. This should also
eliminate the cold air at the west end of The Gorge. Still a
threat of some light -fzra through the morning east of the
terminal, mainly near The Gorge. Will go with a switch to SW
surface wind kpdx to kttd mid to late afternoon. Weishaar.


Marine...a front will bring increasing southwest to west wind with
widespread gusts of 25 to 30 kt this afternoon through early
Sunday evening. Expect the front to push onshore late this
afternoon. Latest models show boundary layer wind speeds of 15 kt
or less between 06z and 12z Mon.

Seas running 10 to 12 ft this morning and are expected to hold in
the 10 to 13 ft range through Sunday evening. A small spike to
around 15 ft for the north waters late tonight. Guidance suggests
seas ease under 10 ft Mon morning. Weishaar.


Pqr watches/warnings/advisories...
Pz...Small Craft Advisory for winds until 6 PM PST Sunday for
coastal waters from Cape Shoalwater Washington to Florence or out
60 nm.

Small Craft Advisory for hazardous seas until 6 PM PST Sunday
for coastal waters from Cape Shoalwater Washington to Florence or
out 60 nm.

Small Craft Advisory for rough Columbia River bar until 4 am
PST Sunday.


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