Gale Warning 3, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland Oregon
932 PM PST Sun Jan 15 2017

.SYNOPSIS...East winds will continue to push cold air through
the Columbia Gorge through tonight and into the Willamette Valley.
Cold air trapped at the surface will keep inversions strong, with
locally poor air quality through Monday. Some areas of night and
morning fog will form in the valleys under the inversion. Milder
temperatures are developing aloft, setting the stage for some
freezing rain in and near the Gorge Monday night and Tuesday as
precipitation associated with an incoming front spreads inland.
Elsewhere, expect rain and much milder temperatures Tuesday and
Wednesday. Heavy rain on top of existing snowpack will bring the
threat of flooding, especially in areas impacted by last week's
snowstorm. A return to colder weather is expected by the end of the
week, with additional systems bringing the threat of snow again at
least down into the hills.

&&

.SHORT TERM...Tonight through Wednesday...Quick update the ttd-dls
pressure gradient jump to -10 mb last hour and winds at the west end
of the gorge have responded, so will be issuing a wind advisory for
east Portland/Vancouver metro area with gusts 40 to 50 mph through
mid morning Monday.

Not too much change overnight with another cold night in snow
covered valley locations. However some mid and high clouds filtering
across the area may do little to moderate low temperatures tonight.
Main change for the update is temperatures in the Gorge and Upper
Hood River Valley for Tuesday.  All guidance shows the areas warming
above freezing Tuesday afternoon but experience shows that the low
level easterly flow will likely allow temperatures to moderate to
near freezing. With that said, strong 950-850 mb southwesterly winds
40 to 50 kts crossing the Cascades Tuesday may be enough to induce
lee side troughing to start onshore flow to scour out the cold air
in the gorge.  If that works out, the amount of freezing rain would
be limited, but not before impacts are felt.  Previous discussion
follows...

The cold air is slow to get out of here, with some areas, especially
over the snowpack remaining below freezing. Fortunately,
precipitation timing is also trending later which will give time for
south winds to increase by early Tuesday morning and mix out the last
of the cold air from most areas except for the Gorge and far east
PDX/VUO metro areas. It is not worth mentioning in the forecast at
this point, but given the timing of precip arrival during the morning
hours on Tuesday, and borderline temperatures during the morning,
feel it is prudent to mention the possibility of a brief period of
freezing rain in a few areas with deep snowpack. Main area of concern
for freezing rain is the Columbia River gorge due to a persistent
east wind through the day Tuesday. Current forecast has freezing rain
continuing into the early afternoon on Tuesday, however some models
continue weak easterly flow through the Gorge into Wednesday. Kept
ongoing forecast for now as persistent WSW flow over the Washington
Cascades should lead to some lee troughing at some point which should
weaken the gradient enough to end the east flow through the gorge.
Would imagine a freezing rain advisory or even ice storm warning may
be needed at some point for portions of or even all of the Gorge and
Hood River Valley.

Issued a flood watch this afternoon to address the flooding threat
Tuesday through Thursday. The recent trend of keeping the first wave
on Monday Night and early Tuesday north of the area has continued.
This means our area will likely avoid a prolonged, multi-day rainfall
event which increases our confidence this event will not be to the
caliber of a February 1996 flood event. However, this does not mean
the threat for flooding is over. Heavy rain is still expected between
Tuesday afternoon and Wednesday night. Rainfall totals of 4 to 8
inches are expected along the Coast and Coast Range, Willapa Hills,
and south Washington Cascades. Much of this rain will fall between
Tuesday evening and Wednesday evening. In addition, low elevation
snow between 0.25" and 1.0" water equivalent will melt quickly,
especially when the heavier rain begins later in the day Tuesday. In
addition to the rainfall forecast, another unknown in the flooding
forecast is the amount of available water equivalent in the snow.
Between 1000 and 2000 feet in the Coast Range, SWE measurements range
between 1 and 6 inches. We don't have the observation resolution to
know just how widespread the 6 inch SWE area is compared to the 1 to
2" water equivalent. Nonetheless, flooding appears likely mid week,
but the exact severity still remains uncertain due some uncertainty
surrounding the amount of rain and the amount of snow water
equivalent available. /Bentley /mh

.LONG TERM...Wednesday night through Sunday...The active weather
pattern continues during the extended forecast. Models continue to
show the jet shifting south of our forecast area by Wednesday night,
with the upper level trough shifting inland by early Thursday. The
jet shifting south should help keep the majority of the precip aimed
at southern Oregon and northern California. However, the upper level
trough will help to maintain cool and showery conditions over the
Pac NW on Thursday and Friday, with snow level lowering to around
2000 ft by Friday. A larger and colder upper level trough looks to
impact the region over the weekend, with an outside chance for low
elevation snow possible on Saturday and Sunday.

&&

.AVIATION...Generally VFR conditions through the period for most
sites. However, fog/low stratus may again develop at KEUG and KHIO
aft 09z through 15z. Expect increasing mid clouds aft 21z from NW to
SE across region ahead of next weather system with rain beginning
by 06z north of a KONP-KDLS line and pushing south after.

KPDX AND APPROACHES...Low-level easterly flow will maintain VFR
conditions through 00z Tuesday, with gusty east winds continuing
over eastern approaches but becoming increasingly confined to the
mouth of the gorge. Increasing mid level clouds Monday ahead of
next system, but expect rain to begin aft 06z Tue.  Cullen

&&

.MARINE...Seas will build to around 8 to 9 ft tonight. Easterly
winds will begin to turn more southerly and increase tonight and
Monday ahead of the next frontal storm system.	Southerly
winds of 25 to 30 kts will move into the waters mid-day Monday
through the afternoon. Gales are possible across the far northern
waters late Monday afternoon and evening and move into the
southern waters Tuesday morning.

Additional fronts will move across the waters through Wednesday.
Southerly winds will increase to solid gales Tues and possibly
low end storm force wind gusts. Coastal jet development will
likely produce locally higher winds within 20nm of the coast
during this time. Given this will be relatively long duration wind
event, seas should climb well above 20 ft Tuesday PM and early
Wednesday AM. A temporary lull in the weather looks to arrive
Thursday before more storm systems keep seas and winds elevated
late in the work week and/or next weekend. tw

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from Tuesday morning through late Wednesday night
     for Central Columbia River Gorge-Coast Range of Northwest
     Oregon-Greater Portland Metro Area-Lower Columbia-North
     Oregon Coast-Upper Hood River Valley-Western Columbia
     River Gorge.

     Flood Watch from Tuesday 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.

     Wind advisory in effect until 10 am pst monday near the gorge.

WA...Flood Watch from Tuesday morning through late Wednesday night
     for Central Columbia River Gorge-Greater Vancouver Area-I-
     5 Corridor in Cowlitz County-South Washington Cascade
     Foothills-South Washington Cascades-South Washington Coast-
     Western Columbia River Gorge-Willapa Hills.

     Wind advisory in effect until 10 am pst monday near the gorge.

PZ...Gale Watch from Monday evening through late Tuesday night for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Small Craft Advisory for winds from 10 AM to 7 PM PST Monday
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 nm.

     Small Craft Advisory for winds from 1 PM to 7 PM PST Monday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     nm.

     Small Craft Advisory for Rough Columbia River Bar from 5 AM
     to 9 AM PST Monday, and from 5 PM to 10 PM PST Monday.

&&

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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.