High Wind in Washington, April 3 to 4, 2022

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
937 PM PDT Sun Apr 3 2022

Updated aviation and marine discussions.

.SYNOPSIS...A storm system will bring increasing winds and
widespread beneficial valley rain and mountain snow late Sunday
through early Tuesday before drier and warmer weather returns
midweek.

&&

.SHORT TERM...Tonight through Tuesday night...The GEFS/EPS ensemble
IVT plume forecast continue to suggest a moderately strong
atmospheric river will impact the region tonight through Monday,
bringing beneficial valley rain and Cascade snow to the region. Radar
and satellite observations from Sunday afternoon already showed this
trend beginning to unfold, with an elongated frontal boundary
extending all the way to the south WA/far north OR coast from a
parent low located in the Gulf of Alaska around 50N/150W. An area of
light stratiform rain was already impacting locations north of
Astoria. The aforementioned parent low will shift southeastward
tonight towards northern Vancouver Island, and the latest iteration
of the NAM/GFS/EURO all suggest this surface low will deepen to
~975mb shortly before making landfall Monday morning. A very strong
jet max (winds close to 165 kt at 250 mb) on the south side of this
low will usher sub-tropical moisture into the area tonight into
tomorrow, which is when periods of moderate to heavy rain are
expected to begin. The heaviest rain will likely occur over southwest
WA, as this area will be under the left-exit region of the jet, which
is a favorable area for rising motion. Strong westerly flow will also
enhance orographic lift and precipitation rates over the mountains,
especially westward-facing slopes. To account for the favorable jet
stream dynamics, ample atmospheric moisture, and strong orographic
lift, decided to blend the latest WPC QPF guidance with the NAM Nest
to increase QPF amounts over the higher terrain a bit.

While flooding is not much of a concern with this storm system, high
winds and heavy Cascade snow will be. The strongest winds are
expected along the immediate coastline, elevations above 1500 feet in
the Coast Range and Willapa Hills, and the high Cascades. These areas
should see peak wind gusts around 55-65 mph, which forecast NAM/GFS
soundings support as well as the NBM v4.1 probabilities. Therefore,
decided to issue a High Wind Warning along the coast near beaches and
headlands and for elevations above 1.5 kft in the Coast Range. Winds
over the interior lowlands of southwest WA and northwest OR should be
weaker with peak gusts around 35-45 mph, but still high enough to
warrant a marginal Wind Advisory. The strongest winds are expected
between 12 AM and 8 AM PDT Monday. After 8 AM Monday, high winds will
become more localized and will be associated with the strongest
showers or thunderstorms (which are expected to occur through the day
and evening). The best chance for thunder still looks to be to the
north of Salem where instability will be deepest and temperatures
aloft will be coldest. The latest SPC SREF calibrated thunderstorm
probabilities back this up well. The atmosphere will feature plenty
of wind shear on Tuesday, and forecast soundings suggest the
strongest showers or storms will be capable of producing wind gusts
in excess of 45 mph. While directional shear looks to be a bit
lacking, low-level speed shear may be high enough for a weak tornado
to spin up (especially if surface winds stay southerly/southwesterly
for long enough, which would help increase directional shear).
Confidence in this is low, and the chance of a tornado occurring at
any given location is extremely slim. Straight-line winds is the
main concern, but any wind damage from that would also be localized.

Elevations above 5000 feet in the Cascades will experience winds
around 40-55 mph through the day (especially above treeline on
westward-facing slopes, which will be exposed to the free
atmosphere). This will create whiteout conditions in the high
Cascades due to a combination of falling snow and blowing snow. Areas
of blowing snow will also significantly reduce visibilities at pass
level. While winds will decrease significantly on Tuesday, strong
orographic lift will continue through the day and favor post-frontal
showers. While models and their ensembles suggest high confidence for
at least some QPF on Tuesday, the NBM v4.0 had very little to no PoPs
across the area. This is a common occurrence for v4.0 in post-frontal
showery scenarios, but v4.1 handles these scenarios much better.
Therefore, decided to blend towards NBM v4.1 PoPs by 50% on Tuesday.
Still expecting storm total snow amounts around 12 to 30 inches, with
the highest amounts above 5000 feet. If you must travel over the
Cascade passes tonight through Tuesday, be prepared for winter
driving conditions and travel restrictions.

Lastly, Tuesday night is still looking chilly as surface high
pressure builds into the area. The NBM is going even lower with
temperatures now, suggesting widespread lows around 32 to 33 degrees
across the lowlands. This means widespread frost is likely to occur
Tuesday night, so be sure to protect any sensitive outdoor vegetation
you may have. -TK

.LONG TERM...Wednesday through Saturday night...The long term
forecast is much more quiet compared to the short term forecast, as
the weather pattern will be turning warmer and drier over the Pacific
Northwest. On Wednesday, models and their ensembles are still showing
an upper level ridge building over the region with the ridge axis
over the Willamette Valley during the afternoon. At the surface, a
thermally-induced surface trough will build northward up the Oregon
coast, potentially pushing slightly offshore during the evening. This
will bring a transition to low-level offshore flow, drier weather,
and warming temperatures. The NBM v4.0 and v4.1 both show high
probabilities for afternoon high temperatures around 65 degrees or
warmer across the interior lowlands on Wednesday. The coast may also
warm into the lower 60s, especially if the thermally-induced surface
trough is able to push offshore a bit and bring east winds all the
way to the coast.

The upper level ridge responsible for the warmer and drier weather on
Wednesday will shift into central and eastern Oregon on Thursday
while temperatures aloft warm even more west of the Cascades. The NBM
1D viewer continues to advertise high probabilities for high
temperatures around 70 degrees or warmer on Thursday, aside from the
coast where highs will likely top out somewhere in the 60s in the
late morning or early afternoon before a sea breeze circulation
develops and cools temperatures back into the 50s. In fact, some
locations in the Willamette Valley may reach into the mid 70s, which
is what the NBM mean is already showing.

The forecast then becomes quite uncertain Friday into the weekend,
but there is an increasing signal for a marine push/return to onshore
flow on Friday. This would bring increasing cloud cover, cooler
temperatures, and a chance of rain to the area. While this outcome is
not certain yet, GFS/EURO ensemble guidance for temperatures and QPF
are favoring this outcome more than the potential drier outcome. -TK

&&

.AVIATION...06Z TAFs: Warm/occluded front to the north over nw WA
with a cold front sagging to the southwest. Low pressure well offshore
will push to Vancouver Isl later tonight into Mon. As it does, will see
strong cold front race across the coastal waters and onshore
around 09-12Z Mon, with front to the Cascades by 14-16Z Mon.

As the front approaches the coast, will see increasing southerly
winds, both aloft and at surface. Surface gusts over 35 kt expected
along the coast through this evening, with gusts 40 to 50 kt
likely 06-12Z especially right near along the coastline. Winds
increase inland overnight, but generally affecting higher exposed
terrain. That said, gusts 25 to 40 kt in Willamette Valley
possible after 09Z, then easing a bit later in the morning.

Flight conditions generally MVFR to IFR at the coast and MVFR
inland. Conditions improve some inland with low VFR and frequent
MVFR with showers in the post frontal air amss. A few thunderstorms
with small hail are possible on coast on Mon, and inland after
18Z, mainly north of Salem. Lots of wind energy aloft for
thunderstorms to mix down to the surface Monday, so winds can
change dramatiacally with showers or thunderstorms.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...Rain continues overnigh with increasing
south winds, will see MVFR condition becoming more prevalent.
Moderate southerly winds aloft later tonight, with gusty winds at
surface. Appears strongest surface gusts at field area look to be
25 to 35 kt between 09Z and 16Z around as the front moves
through. Post frontal showers continue through the day with good
potential for gusty winds to continue, especially with showers and
possible thunderstorms in the area. Shower and winds ease Monday
evening. /mh

&&

.MARINE...Update: Gale force gusts occuring over the waters this
through this evening so far. Expect more of an increase in then
next several hours as the cold front approaches. Current forecast
looks good and follow trends of models.
Previous discussion follows...

Deepening low pres well offshore will push to Vancouver Island
later tonight into Monday. This will push a rather strong cold
front across the coastal waters tonight, with strong southerly
winds as the pressure gradient tightens. Generally, south winds 15
to 25 kt this afternoon/early evening will increase this evening,
running 25 to 30 kt by late evening. After midnight, south winds
will gust up to 45 kt as the fronts arrives. Front will push
onshore 4 to 6 am Monday, with sharp change to more southwesterly
winds. Wind speeds will drop a bit, but gale force gusts will
remain through the morning. With the showers and thunderstorms
around the region on Mon, will still have some locally strong
gusts of 45 to 50 kt at times. But, these should not be
widespread, as will be more confined to areas around the squalls
of showers.

Bigger story may be the seas. Rather choppy and wind driven
tonight, with seas building to 17 to 20 ft overnight. But, will
see heavy baseline swell arriving during the day on Monday, with
west swell of 19 to 23 ft in the afternoon through Mon night.
That, along with the gusty winds, will push combined seas to 21 to
perhaps as much as 25 ft for a time Mon evening. Either way, not
all that great of a time to be on the waters.

Winds will gradually ease Mon night into Tue, while seas will take
a bit more time to lower. At this time, appears seas start Tue am
around 18 to 20 ft, but drop back to around 15 ft Tue afternoon,
and bit lower Tue night.

Weather starts to quiet down a bit during the middle of the week,
as high pressure builds offshore. This will bring northerly winds
10 to 15 kt to coastal waters. At same time, seas subside towards
sub 10 ft.

BEACH HAZARD...Rather chaotic and potentially dangerous
conditions for those in and near the surf zone over the next 48
hours. Expect choppy surf and strong gusty south to southwesterly
winds tonight into Monday morning. Winds turn more westerly
during the day Monday, maintaining choppy surf zone. In addition,
will see increasing west swell through the day, with longer
periods. This will be enough to warrant High Surf Advisory
conditions for Monday afternoon into early Tuesday morning.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 11 PM PDT Monday for Central Oregon
     Coast-North Oregon Coast.

     High Surf Advisory from noon Monday to 11 AM PDT Tuesday for
     Central Oregon Coast-North Oregon Coast.

     High Wind Warning until 8 PM PDT Monday for Central Coast Range
     of Western Oregon-Coast Range of Northwest Oregon.

     Wind Advisory until 8 PM PDT Monday for Central Willamette
     Valley-Greater Portland Metro Area-Lower Columbia-South
     Willamette Valley.

     Winter Storm Warning until 5 AM PDT Tuesday for Cascades in Lane
     County-Northern Oregon Cascades.

WA...High Wind Warning until 11 PM PDT Monday for South Washington
     Coast.

     High Surf Advisory from noon Monday to 11 AM PDT Tuesday for
     South Washington Coast.

     High Wind Warning until 8 PM PDT Monday for Willapa Hills.

     Wind Advisory until 8 PM PDT Monday for Greater Vancouver
     Area-I-5 Corridor in Cowlitz County.

     Winter Storm Warning until 8 AM PDT Tuesday for South
     Washington Cascades.

PZ...Small Craft Advisory until 11 AM PDT Tuesday for Columbia River
     Bar.

     Gale Warning until 5 AM PDT Tuesday for coastal waters from
     Cape Shoalwater WA to Cascade Head OR out 60 nm.

     Gale Warning until 8 PM PDT Monday for coastal waters from
     Cascade Head OR to Florence OR out 60 nm.

&&

www.weather.gov/portland

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