High Wind in Washington, November 19, 2024

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1028 AM PST Tue Nov 19 2024

Updated Aviation Discussion

.SYNOPSIS...Scattered showers continue across the area this
morning, with lingering winter weather impacts in the Cascades.
A powerful system approaches the coastal waters today, bringing
strong winds to the coast and breezy conditions to the interior
valleys this afternoon through early Wednesday morning. This
system will also bring another round of heavy snow to the High
Cascades. Wet weather continues through the end of the week, but
the probability for significant hydro impacts has diminished
with time as a strong atmospheric river remains south of the
area.

&&

.DISCUSSION...Tuesday through Monday...Radar imagery early
Tuesday morning shows scattered showers still continuing across
much of NW Oregon and SW Washington. Area webcams observe snow
continues to fall over the Cascade passes in areas of showers.
These showers are expected to continue across the region today
along with a 15-20% chance of isolated thunderstorms along the
coast through this morning. Cascade snow will be on the lighter
side through this afternoon with an additional 3-6 inches at
pass level. Weather spotter reports from late last night into
early this morning indicate snow levels have fallen to around
1500 feet with accumulating snow around 1-2 inches. Snow levels
should raise back to around 2000-2500 feet by daybreak and
continue rising through the day to around 4000 feet by late
afternoon. A Winter Weather Advisory remains in effect through
10 AM Wednesday. More on the winter conditions tonight below.

Ensemble guidance remains in solid agreement of an
exceptionally strong low pressure system undergoing rapid
cyclogenesis in the eastern Pacific today. The GFS, Euro, and
Canadian ensembles all indicate rapid strengthening of the low
with pressure bottoming out at 940-950 mb around 350-400 miles
off of the Oregon and Washington coasts. This will bring a
strong frontal system through the Pacific NW this afternoon
through tonight with strong winds being the main impact of
concern. The front is expected to move through the waters
beginning late this morning, producing Storm Force winds (gusts
over 48 kts/55 mph) along with a period of Hurricane Force winds
(gusts over 64 kts/74 mph) in the waters beyond 10-20 miles
offshore. Along the coast and over the higher elevations inland,
wind gusts up to 50-60 mph are possible. For locations inland
elsewhere, expect gusts up to 35-45 mph. A High Wind Warning for
the coast and the Coast Range as well as a Wind Advisory for
the interior valleys is in effect from 1 PM this afternoon
through 4 AM Wednesday, though winds will begin increasing
before and remain breezy after this period. One point to note is
the differing probabilities between the NBM and HREF on
stronger wind gust chances. Both models indicate a 60-90% chance
of gusts over 50 mph along the coast, Coast Range, and higher
Cascades. However, HREF indicates anywhere from a 20-60% chance
of gusts over 70 mph and a 10% chance of gusts over 80 mph along
the coast whereas NBM indicates 5-10% and less than 5%
respectively. Additionally, HREF indicates a 40-50% chance of 50
mph wind gusts could push inland into the central and southern
Willamette Valley along the frontal passage whereas the NBM
indicates only a 5-10% chance. The main takeaway from this is
this indicates this is the area that will likely see the
strongest wind gusts in the valley, even if gusts don't reach
50+ mph.

A surge of Pacific moisture is also associated with this weather
system. IVT values will peak around 500-750 kg/ms along the
Oregon coast, indicating a moderate atmospheric river, though
since the timing of peak IVT values will be less than 24 hours,
rain impacts from this storm will be minimal. Widespread rain is
expected to push into the area this afternoon with periods of
moderate to heavy precipitation this evening into the overnight
hours as the front moves through. Scattered showers, some
strong, along with coastal thunderstorm chances continue into
the day Wednesday into Thursday. Most likely 24 hour
precipitation amounts from 10 AM today to 10 AM Wednesday are
0.75-1.25 inches for interior lowlands and 1.5-3 inches for the
coast and mountains. The high end scenario (90th percentile) is
not much higher with 1.25-1.75 inches for the interior lowlands
and 2-4.5 inches along the coast and mountains. Flooding is not
expected with either of these scenarios apart from localized
urban flooding for poor drainage areas during periods of heavier
rainfall. Snow over the Cascades is also expected to pick up
tonight, though snow levels will rise to 4000-4500 feet by
around midnight. An additional 6-12 inches of snow is forecast
at pass level from 4 PM today through 10 AM Wednesday.

Ensembles are now in good agreement that the surge of
atmospheric river moisture will be pushed south into northern
California fairly quickly on Wednesday, remaining funneled there
into Thursday. However, ensembles are coming into better
agreement on the next storm system forming another closed low
moving from south to north starting offshore of the northern
California coast generally late Thursday and pushing along
waters off of the Oregon coast into the waters off of the south
Washington coast by sometime Friday morning. This would bring
the atmospheric moisture back into NW Oregon and SW Washington,
bringing another round of widespread rain to the area. However,
significant uncertainty remains in terms of timing and location
of the low as well as strength of the moisture plume. In terms
of rain, even with the differences in peak IVT (500-700 kg/ms
from the Euro vs around 250 kg/ms from the GEFS), the high end
scenario is very similar if not slightly less than the high end
scenario for tonight's storm. Therefore, flooding impacts are
again not expected. Winds could be the bigger concern once again
with this storm. If the low ends up pushing closer to the coast,
this could produce another round of elevated southerly winds.
Guidance isn't showing much in the way of this concern at this
time, but will be keeping an eye on this system as it
progresses.

Periods of precipitation will continue through the weekend into
nearly next week as ensemble guidance indicates an unsettled
weather pattern continues. WPC 500 mb clusters vary quite
significantly in specifics, but all clusters indicate the
possibility of another, weaker weather system moving through the
region at some point in this time period with showers continuing
in between systems. -HEC

&&

.AVIATION...A mix of VFR/MVFR conditions with isolated pockets of
IFR persist across the airspace. Scattered showers will continue
to move northward, with a brief lull ahead of a very strong front
expected to cross the airspace starting after 00Z Wednesday and
will bring rain and very strong, gusty south/southwesterly winds
across the airspace.

Gusts along the coast up to 55 kt will be possible with the
highest gusts expected south of KTMK. Inland locations should
expect gusts up to 35 kt. These gusty conditions are expected to
persist through at least 12Z Wednesday.

Given the very gusty conditions, LLWS in the form of speed shear
will be potential issue through 12Z Wednesday across the
airspace.

PDX APPROACHES...A mix of VFR/MVFR conditions through the TAF
period. Strong front will bring rain, gusty winds (gusts up to
35 kt) as well as the potential for LLWS in the form of speed
shear through 12Z or so on Wednesday. -Batz/42

&&

.MARINE...Conditions become treacherous as a strong storm
approaches the waters today. This will bring Hurricane Force
wind gusts to outer waters, as well as Storm Force winds to the
inner waters and the Columbia River Bar by late this morning.
Expect gusts up to 75 kt for the outer waters, with gusts up to
55 kt elsewhere. Strong winds and a large incoming swell will
cause seas to build towards 24 to 28 ft with a 20% probability
of 30 ft seas or greater for the outer waters. By late tonight,
winds should subside towards very strong Gales and then continue
to subside towards Small Craft Advisory gusts by Wednesday
night.

Seas will remain elevated but will slowly subside through
Wednesday night towards 19 to 21 ft and will continue that trend
through Thursday. However, the next system is expected to bring
another round of elevated winds and seas by Friday. There still
remains a fair amount of uncertainty with the Friday system and
models are varied in strength and track of the low. As a result am
keeping strong Small Craft gusts in the forecast with seas in the
11 to 14 ft range. /42

&&

.BEACH HAZARDS...Large waves and hazardous surf conditions
starting late tonight through Wednesday afternoon, with breakers
of 21 to 26 ft expected.

Destructive waves may wash over beaches, jetties, and other
structures unexpectedly. People can be swept off rocks and jetties
and drown while observing high surf. Minor beach erosion may
damage coastal properties and buildings. Higher than normal water
run-up is expected on beaches and low-lying shoreline.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 AM PST Wednesday for ORZ101>103-106-
     107.
     High Surf Advisory from 7 PM this evening to 4 PM PST
     Wednesday for ORZ101>103.
     Wind Advisory until 4 AM PST Wednesday for ORZ108>118.
     Winter Weather Advisory until 10 AM PST Wednesday for
     ORZ126>128.
WA...High Wind Warning until 4 AM PST Wednesday for WAZ201.
     High Surf Advisory from 7 PM this evening to 4 PM PST
     Wednesday for WAZ201.
     Wind Advisory until 4 AM PST Wednesday for WAZ204>207.
     Winter Weather Advisory until 10 AM PST Wednesday for WAZ211.
PZ...Gale Warning until 1 PM PST this afternoon for PZZ210.
     Storm Warning until 4 AM PST Wednesday for PZZ210.
     Storm Warning until 4 AM PST Wednesday for PZZ251>253.
     Storm Warning until 1 PM PST this afternoon for PZZ271>273.
     Storm Warning from 10 PM this evening to 4 AM PST Wednesday
     for PZZ271>273.
     Hurricane Force Wind Warning until 10 PM PST this evening for
     PZZ271>273.
&&

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