Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 171113
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
312 AM PST Tue Jan 17 2017

.SYNOPSIS...Milder and much wetter weather arrives today. But will
have areas of freezing rain across the interior this am, with that
area slowly contracting to be the Gorge/Hood River Valley out through
the eastern Portland/Vancouver metro tonight. But nearly all areas
will see warmer temperatures on Wed as region as offshore flow wanes.
Rather heavy rain at times tonight through Wed, and combined with
snow melt, will see large rises on rivers. At this time, flooding is
not expected, but small streams will have to be closely monitored
tonight and Wed. After Wed night, will see more typical January
weather, with mild and wet conditions, and snow levels lowering back
to or just below the passes.
&&

.SHORT TERM...Today through Thursday...Much milder air will stream
into the region later tonight as rather strong jet offshore pushes
mild and wet front into the region. But first system is not all that
impressive, and will push light rain across the region this am. Now,
still have decent amount of offshore flow over the region, enough so
that temperatures are holding steady in the mid to upper 20s over
much of the interior. Coldest air in in the Columbia Gorge, where
temps area in the lower to middle teens. As the light rain heads
inland this am, it will easily freeze upon contact with surfaces,
with generally light coating of ice expected. Heaviest will be up to
a tenth of an inch around the North Willamette Valley/Clark County
into the Columbia Gorge. Precipitatiion more spotty as move south in
the Willamette Valley, with less than 0.05 inch of ice expected. But,
does not take much ice to make roadways/bridges/sidewalks quite
treacherous.

Will have a period from late morning into early afternoon here may
just wind up with clouds and some light occasional precipitation. But
do not be lulled into thinking the freezing rain threat is over. Even
though pres gradients will ease, with bit less east wind, air mass
trapped in the interior lowlands will still be cool, and even below
freezing in areas of North Willamette/Clark County and eastward.

Next wave of rain will spread onshore by early afternoon, and spread
inland this afternoon. This will be accompanied by rather strong and
warm 850 mb (about 5000 ft) southerly winds. As warmer temperatures
arrive, will see breezy southerly winds over the higher terrain, with
freezing level rising to around 8000 to 9000 feet. Fairly deep warm
layer aloft so all precipitation will be rain for most areas. Even in
the mid and south Willamette Valley, temperatures will be moderating
to the lower to mid 40s later this afternoon as southerly winds start
punching into the lowlands. But different story for those areas where
sub-freezing temperatures are trapped and maintained by light to
moderate easterly winds. Yep, those areas will be the Hood
Valley/Columbia Gorge, and across parts of Clark County and the North
Willamette Valley. At moment, think will take until early evening for
areas west of Portland to moderate above 32 deg, but may not be until
around or after midnight for downtown Portland and Vancouver to warm
above freezing. Areas closer to Troutdale will not see 32 deg until
later Tue night. This will ensure decent shot of icing for late this
afternoon into much of the evening for those areas. Current Ice Storm
Warning in effect, for 0.10 to 0.25 inch of ice in Washington County,
but 0.35 to 0.75 for areas from West Hill eastward, and 0.75 inch or
more for areas along the Columbia River from WA Rte 14 to Burnside St
in Portland, and east of I205. Now, icing in the Columbia Gorge, Hood
Valley, and areas in south Washington Cascades such as White Salmon
Valley will be much heavier, generally 1 to 2 inches thick, as
temperatures there will not moderate until sometime Wed.

But that`s not all folks. Those along the coast will have increasing
southerly winds today, with gusts 65 to 80 mph likely tonight into
early Wed am. Strongest winds will be just ahead of the front that
will push onshore Wed am. Even higher ridges in the Coast Range and
Willapa Hills will see strong gusty south winds tonight, with gusts
there 55 to 70 mph, especially on exposed ridges.

And behind door number three...heavy rains and snowmelt tonight and
Wed. Models have been easing back on rainfall amounts, but with front
slowly working its way inland tonight and Wed am, still good
potential for 3 to 5 inches of rain over the Coast Range, and in
parts of the Cascades, with generally 1 to 2 inches of rain for the
interior lowlands. While this alone would not bring flooding, it is
the current snow on the ground that will add extra waters as it
melts. Have Flood Watch up for the region for tonight through Wed. At
this time, do not anticipated flooding problems on key rivers, but
small streams will have to be closely monitored as will see large
jumps in levels tonight into Wed. More likely will be the issue of
urban flooding, as city storm drains could be blocked by broken twigs
and debris from past ice storms such as in Eugene, or by snow and
slushy slurry debris that will see in Portland/Vancouver metro as the
snow melts tonight and Wed.

Front will finally push inland and across region on Wed, with
temperatures everywhere moderating above freezing, even in Hood River
albeit it may not be much above freezing until Thu. Generally showery
and more seasonable temperatures for Thursday, with snow levels at
3500 to 4000 feet.                              Rockey.


.LONG TERM...Thursday night through Monday...Models remain in decent
agreement that the progressive weather pattern will continue through
the extended forecast, albeit with some slight timing differences. A
deepening upper level low looks to approach the Pac NW late Thursday
and swing a cold front across the forecast area on Friday which will
bring another round of gusty winds and more rain. Conditions look to
become more showery Friday night as the trough shifts inland. Colder
air aloft will filter in over the region during this time with snow
levels lowering to around 2000 ft by Saturday morning. Showers look
to continue on Saturday as a weak shortwave trough moves across the
region. Another upper level trough will approach the area Sunday and
swing another frontal system across the Pac NW. Post frontal showers
look to persist into early next week under northwesterly flow aloft,
with snow levels remaining below 2000 ft. There is still a chance of
low elevation snow during the extended forecast, but confidence is
extremely low. Nonetheless, keep an eye on the forecast as things
may change in the coming days. /64
&&

.AVIATION...Low level offshore flow early this morning will trend
towards a moister southerly flow regime, which will result in
deteriorating flight conditions at many terminals. In addition, a
round of light freezing rain will likely fall at the Willamette
Valley taf sites between ~13-17z Tuesday with less than a tenth
of an inch of ice accumulation expected. A break in the freezing
rain then appears likely with sites like KSLE and KEUG likely
rising above freezing. However, another round of rain will move
into the region towards 21z Tuesday, and will likely fall in the
form of freezing rain at the PDX metro taf sites into at least the
evening hours...and quite likely beyond 12z Wednesday for KTTD.
Ice accumulations of 0.50-1.00" or more will be possible near the
Columbia River Gorge at KTTD.

KPDX AND APPROACHES...The main weather story will be freezing
rain potential. The first round looks light and will likely fall
between ~13-17z Tuesday with less than a tenth of an inch of
accumulation. Due to cold temperatures it will easily accumulate.
There should be a substantial break in the freezing rain
thereafter and temperatures may even temporarily rise above
freezing around midday before a heavier and more solid round of
freezing rain likely falls after 21z Tuesday that lasts well into
the night. Ice accumulations of 0.50" or more appear likely with
this second round. Low level offshore flow during this time will
produce primarily VFR conditions through 12z Wednesday. The main
exception to this will be after 06z Wednesday when an increasingly
saturated lower atmosphere could result in off and on MVFR
conditions. /Neuman

&&

.MARINE...Winds have been very slow to rise overnight, but should
rise into gale force criteria in the next few hours. Winds will
increase further this afternoon and evening with winds likely
increasing into Storm Force criteria with gusts to 50 kt. A
strengthening coastal jet will likely produce stronger wind gusts
within 20nm of the coast tonight. This will likely result in seas
climbing above 20 ft for an extended period beginning this evening
and lasting into early Wednesday morning. Winds should relax from
north to south across the waters Wednesday, which will allow seas
to subside Wednesday afternoon and evening.

Models suggest another deep low pressure system could bring
another round of strong winds and high seas to the waters late in
the work week. Swells associated with this storm system will
arrive from a more westerly direction, and may result in High Surf
criteria being met. /Neuman


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Ice Storm Warning from 6 AM this morning to 6 PM PST Wednesday
     for Central Columbia River Gorge-Upper Hood River Valley-
     Western Columbia River Gorge.

     Flood Watch from this evening through late Wednesday night for
     Cascade Foothills in Lane County-Central Coast Range of
     Western Oregon-Central Oregon Coast-Central Willamette
     Valley-Northern Oregon Cascade Foothills-South Willamette
     Valley.

     Freezing Rain Advisory from 6 AM this morning to 6 PM PST this
     evening for Northern Oregon Cascade Foothills-Northern
     Oregon Cascades.

     Flood Watch from 10 AM PST this morning through late Wednesday
     night for Coast Range of Northwest Oregon-Greater Portland
     Metro Area-Lower Columbia-North Oregon Coast.

     Ice Storm Warning until 10 PM PST this evening for Greater
     Portland Metro Area.

     Freezing Rain Advisory until 2 PM PST this afternoon for Coast
     Range of Northwest Oregon-Lower Columbia.

     High Wind Warning from noon today to 4 PM PST Wednesday for
     Central Coast Range of Western Oregon-Coast Range of
     Northwest Oregon.

     High Wind Warning from noon today to 10 AM PST Wednesday for
     Central Oregon Coast-North Oregon Coast.

     Freezing Rain Advisory until 10 AM PST this morning for South
     Willamette Valley.

     Freezing Rain Advisory until 2 PM PST this afternoon for
     Central Willamette Valley.

WA...Ice Storm Warning from 6 AM this morning to 6 PM PST Wednesday
     for Central Columbia River Gorge-South Washington Cascades-
     Western Columbia River Gorge.

     Flood Watch from 10 AM PST this morning through late Wednesday
     night for Greater Vancouver Area-I-5 Corridor in Cowlitz
     County-South Washington Cascade Foothills-South Washington
     Coast-Willapa Hills.

     Ice Storm Warning until 10 PM PST this evening for Greater
     Vancouver Area.

     Freezing Rain Advisory until 2 PM PST this afternoon for I-5
     Corridor in Cowlitz County.

     High Wind Warning from noon today to 10 AM PST Wednesday for
     South Washington Coast.

     Freezing Rain Advisory until 6 PM PST this evening for South
     Washington Cascade Foothills.

PZ...Storm Warning from 1 PM this afternoon to 10 AM PST Wednesday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Gale Warning until 1 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 4 PM
     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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