Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 231128
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
328 AM PST Sat Feb 23 2019


.SYNOPSIS...An unseasonably cold and unsettled weather pattern will
continue for much of the next week with low elevation snow possible
Sunday night into Monday, particularly north of a line extending
between Salem and Mt Hood.

&&

.SHORT TERM...Today through Monday...Another very busy night here at
the forecast office. Will try to elaborate further on the rationale
behind the forecast after products go out, but here is a preliminary
summary of the adjustments which will be made to our package of
winter highlights this morning:

- Winter Storm Watch upgraded to a Warning for North Oregon Cascades
and foothills tonight and Sunday... 12 to 24 inches of snow expected.

- Winter Storm Watch upgraded to a Warning for Lane County Cascades
tonight through Monday morning... 18 to 36 inches of snow expected.

- Winter Weather Advisory for the west and central Columbia Gorge and
Hood River Valley tonight through Sunday morning... 2 to 6 inches of
snow expected.

- New Winter Storm Watch for the west and central Columbia Gorge and
Hood River Valley late Sunday night through Monday night... 4 to 12
inches of snow possible, followed by a possible transition to
freezing rain west of Cascade Locks.

- New Winter Storm Watches for the Greater Portland and Vancouver
metro area, Central Willamette Valley, North Oregon Coast and Coast
Range, Lower Columbia, and I-5 Corridor late Sunday night through
Monday... 2 to 8 inches of snow possible, heaviest in and near the
Coast Range. Additional freezing rain possible near Troutdale and
Washougal Monday night.

- New Winter Storm Watch for South Washington Cascades and Foothills
Sunday night through Monday night... 6 to 18 inches of snow possible,
followed by possible freezing rain in the valleys.

- New Winter Storm Watch for the North Oregon Cascades and Foothills
Sunday night through early Tuesday morning... an additional 12 to 24
inches possible.

Quick summary of the rationale behind this: Frontal zone will stall
as expected near the Lane/Douglas County border before weak wave of
low pressure develops along the front and moves onshore early Sunday
morning, enhancing precipitation along the front. Snow will be heavy
in the Cascades and foothills, but snow levels are expected to stay
just above the valley floors even to the north of the low/front. Next
wave of low pressure follows, with a track slightly north of the 00z
ECMWF favored, with landfall somewhere near Lincoln City Monday
morning. This is still far enough south for significant lowland
snowfall to the north of the low as it tracks E-NE toward Mount Hood
and disintegrates. The northern extent of significant snowfall
remains in question, but it appears the heaviest snow will remain
south and east of the Willapa Hills. It still looks like portions of
the Oregon Cascades will receive 2 to 4 feet of snow between now and
Tuesday morning. To the south of the low/front, we may have some
urban/small stream flood concerns due to rising freezing levels and
heavy QPF. Coastal rivers may threaten to flood as well, mainly in
southern Lincoln and Lane Counties.  Weagle

.LONG TERM...Monday night through Friday...No changes...Previous
discussion from Friday afternoon follows...The forecast for the
remainder of the upcoming week remains complicated due to
significant model differences so will continue to use a blend of
models rather than a single deterministic model. The general trend
is for the active weather pattern to continue through the week as
additional disturbances moves approach the region. Will continue to
see a potential for low elevation snow the the middle of the week,
but snow levels look to rise about 2000 feet for the second half of
the week. /64


&&

.AVIATION...Fog and low stratus continues to develop across
portions of the interior lowlands despite the showery and only
modestly unstable air mass. Latest satellite and surface
observation trends reveal that the air mass is remaining well-
mixed in the vicinity of stronger showers. Meanwhile, the remains
of the cold front are bringing steadier precipitation to an area
mostly along and east of a KCZK to KSLE line. Dewpoint
depressions remain very small, so may yet see some expansion of
the fog and low clouds. Conditions should improve to mainly VFR
over the interior by late morning or early afternoon Saturday.
However, a weak low pressure system is expected to form along the
stalled cold frontal boundary offshore and move onshore along
the central Oregon coast by nightfall, resulting in steadier rain
and likely MVFR cigs by evening from around KSLE southward.

KPDX AND APPROACHES...Periods of IFR fog/low stratus will impact
the terminal at times through mid-morning. Otherwise, expect
mainly MVFR conditions tonight, with the occasional light shower
overnight, and lifting to VFR by late Saturday morning.   Cullen

&&

.MARINE...Relatively light northwest winds remain across the
waters through the day today. and should remain so through the
day Saturday. Forecast models suggest that a weak low will form
along the stalled cold frontal boundary, and ride along the
boundary until it pushes onshore somewhere near Florence late Sat
night. Expect southerly winds to increase on the south side of
this low, reaching gusts of 25 to 35 kt. There is a chance that
these winds will impact the very southern portions of the coastal
waters late tonight (generally offshore of Florence and south),
depending on exactly where the low tracks. Winds will be out of
the N-NE and much lighter on the north side of the low.


A stronger low is expected to form along the quasi-stationary
frontal boundary on Sunday into Monday. It will likely make
landfall somewhere along the Oregon coast, but the location is
still somewhat uncertain at this time. Areas to the south of the
low look to have a good chance to see gale force winds late Sun
night into Mon morning, potentially some high end gales. To the
north of the low center, winds will be offshore and will
potentially gust to small craft advisory speeds as well. Active
weather looks to continue next week, but forecast details are
highly uncertain at this time.

Seas are expected to build to near 11 feet later today. Seas then
lower below 10 ft early next week. However, there will be
potential for sees to briefly build back into the teens late
Sunday night and into Monday. This is particularly true if gale
strength winds develop across the coastal waters. Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 8 PM this evening to 11 AM PST
     Sunday for Central Columbia River Gorge-Upper Hood River
     Valley-Western Columbia River Gorge.

     Winter Storm Watch from late Sunday night through late Monday
     night for Central Columbia River Gorge-Upper Hood River
     Valley-Western Columbia River Gorge.

     Winter Weather Advisory until 4 AM PST early this morning for
     Northern Oregon Cascade Foothills-Northern Oregon Cascades.

     Winter Storm Warning from 6 PM this evening to 4 PM PST Sunday
     for Northern Oregon Cascade Foothills-Northern Oregon
     Cascades.

     Winter Storm Watch from Sunday evening through late Monday
     night for Northern Oregon Cascade Foothills-Northern
     Oregon Cascades.

     Winter Weather Advisory until 7 AM PST this morning for
     Cascades in Lane County.

     Winter Storm Warning from 4 PM this afternoon to 10 AM PST
     Monday for Cascades in Lane County.

     Winter Storm Watch from late Sunday night through Monday
     afternoon for Central Willamette Valley-Coast Range of
     Northwest Oregon-Greater Portland Metro Area-North Oregon
     Coast.

     Winter Storm Watch from late Sunday night through Monday
     afternoon for Lower Columbia.

WA...Winter Weather Advisory from 8 PM this evening to 11 AM PST
     Sunday for Central Columbia River Gorge-Western Columbia
     River Gorge.

     Winter Storm Watch from late Sunday night through late Monday
     night for Central Columbia River Gorge-Western Columbia
     River Gorge.

     Winter Storm Watch from late Sunday night through Monday
     afternoon for Greater Vancouver Area.

     Winter Storm Watch from late Sunday night through Monday
     afternoon for I-5 Corridor in Cowlitz County.

     Winter Storm Watch from late Sunday night through Monday
     evening for South Washington Cascade Foothills-South
     Washington Cascades.

PZ...Small Craft Advisory for hazardous seas until 6 PM PST this
     evening for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 NM.

     Small Craft Advisory for hazardous seas from 10 AM this morning
     to 6 PM PST this evening for Coastal Waters from Cascade
     Head OR to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 10 AM
     PST this morning.

     Small Craft Advisory for Rough Columbia River Bar from 5 PM
     this afternoon to 11 PM PST this evening.

&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.



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