Blizzard and Winter Storm in Washington, January 8 to 10, 2024

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
833 PM PST Mon Jan 8 2024

Updated aviation discussion and WWA headlines

.SYNOPSIS...The beginnings of what will be an active winter weather
pattern are taking shape over the Pacific, with significant
implications for the weather across SW Washington and NW Oregon later
on this week. But for tonight, expect mostly rain and increasing
south-southwest winds ahead of an incoming cold front. Colder air
behind the front will cause initially high snow levels to plummet,
with snow levels reaching the foothill elevations by midday Tuesday.
Dangerous blizzard conditions will occur along the Cascades above
roughly 3000 feet Tuesday into Tuesday night, which includes the
passes. Low pressure moving into the cold air will bring the
potential for lowland snow to the north of its track Tuesday night,
but there is a lot of uncertainty in said track. Cold air appears
likely to linger across or near the forecast area well into the
upcoming week, with additional systems bringing more chances for snow
and ice to the lowlands through the upcoming weekend.

&&

.DISCUSSION...Tonight through next Monday...As of 330 PM PST Monday
afternoon, latest radar imagery and surface observations suggest that
while a warm front aloft moved pretty quickly eastward through the
forecast area, the surface warm front remains hung up across the
south PDX metro and along Portland's West Hills. On the warm (south)
side of this front, S-SW winds are already increasing with gusts as
high as 45 mph already reported along the coast, with gusts 25-35 mph
inland. On the cold (north and east) side of the front, temperatures
remain in the 30s and lower 40s. It remained cold enough for a couple
inches of snow in the Hood River Valley Parkdale and above; this has
since mostly changed to rain or freezing rain as warmer air moves in
aloft.

Winds will continue to increase this evening as a strong cold front
approaches the coast, prompting us to issue High Wind Warnings along
the N OR/S WA coast and the adjacent terrain. Gusts 45-60 mph are
likely tonight for the coastal communities, with up to 70 mph gusts
possible for exposed beaches and coastal headlands. Given excellent
mixing and a strong synoptic wind profile aided by a bent-back
occlusion (aka "sting jet"), strong westerly wind gusts will persist
for several hours behind the front, causing us to keep the High Wind
Warning up throughout the day Tuesday. This is also the case for our
inland valleys north of Albany, where gusts may reach 50 mph, even
for the lowlands. An increasingly unstable air mass Tuesday means
easier momentum transfer from the strong winds aloft, so any heavy
showers or thunderstorms would probably come with gusty winds (and
small hail).

Since nearly every winter weather hazard is in play somewhere across
SW Washington and NW Oregon this week, I will just focus on the
weather expected to make the greatest impacts and/or any significant
changes we made to the forecast.

The biggest change we made was earlier in the shift, introducing snow
potential to the lowlands Tuesday night into Wednesday. Guidance
began to hint at this possibility 24-36 hours ago as they latched on
to a shortwave emerging off Japan. This system will be whisked across
the Pacific by a strong and zonal jet stream, making landfall
somewhere in the Pac NW Tuesday night. Given the fast flow pattern
and subtle features involved, uncertainty on where this landfall will
occur is high and unfortunately this landfall location is immensely
important to the forecast. Colder air to the north of the low's track
will lead to much lower snow levels than to its south. This system
will have abundant moisture involved, as the Scripps Center for
Western Weather and Water Extremes (CW3E) guidance suggests a weak
atmospheric river is in play as the system moves onshore. Forcing
will be impressive as post-frontal cold air pushes back against the
mild Pacific air the low is trying to bring onshore, enhancing
frontogenesis, especially at the surface. Given the forcing and
moisture involved with this system, whoever ends up getting snow from
this system could potentially see a lot of it.

Models have been honing in on somewhere along the north Oregon coast
as the landfall location Tuesday night. With 850 mb temperatures in
the -3 to -5 deg C range and fairly strong S-SW flow ahead of the
low, conditions look marginal at best for snow levels to reach the
valley floors, even on the colder north side of the system. That
said, this system is highly dynamic and has the potential to produce
heavy enough precipitation to drag snow levels lower than they
otherwise would be, largely due to evaporational cooling and the
latent heat absorption by melting snowflakes aloft. If this lasts
long enough - and the latest NAM soundings suggest it will - rain may
change to wet snow across the Portland/Vancouver metro Tuesday
night... with the better chance being in the northern Clark County
suburbs like Battle Ground and Yacolt. That said, if the low tracks
farther south, these chances also shift south. At this point, it
appears there will be a 20-40 mile wide stripe where rain changes to
snow down to the lowest elevations Tuesday night into Wednesday
morning, with up to a slushy inch or two of snow for the valley
floors and perhaps up to as much as 3-6 inches above 1000 feet. The
12z HREF supports this with a 20-40% chance of any accumulating snow
for the lowlands Albany northward, and as much as a 20% chance of 4
or more inches of snow across a few swaths of the valley. This likely
represents a handful of 12z HREF members that have this stripe of
lowland snow, but have it in different locations. So this adds
confidence to the potential for snow at least down to 500-1000 feet
for at least a portion of the lowlands. The problem is that we don't
really know where this stripe will be at this point - this forecast
will become refined as more HREF members make it into the mix.

With all this talk of lowland snow, we should not lose the fact that
the Cascades appear on track for a high-end winter weather event.
Blizzard conditions Tuesday, with significant snow expected to linger
through much of Wednesday, will make travel - or even just being
outside - dangerous for the mountains above 3000 feet. This includes
the Cascade passes, where travel will become extremely challenging
and hazardous Tuesday into Wednesday, even for the most experienced
of drivers. Deep moisture with conditional instability, exceptional
upslope orographic enhancement, and strong synoptic forcing, will
result in snow being measured in feet for the passes and above
Tuesday and Wednesday, rather than inches. By the time all is said
and done and precip tapers to scattered snow showers, up to 2 feet of
snow is likely for the higher Cascade foothill elevations, with up to
4 feet of snow for the higher ski resort elevations. With many models
showing 45-60 kt west winds between 850-700 mb, winds will be very
strong with gusts up to 55 mph for the passes and 75 mph for the
higher ski resort elevations. The combination of heavy snow and
strong winds will lead to white-out conditions at times. Anyone who
insists on travelling across the Cascades Tuesday or Tuesday night
should absolutely make sure someone knows where they are going, that
their cell phone is charged, and that they have a winter survival kit
packed in their vehicle.

Whatever happens Wednesday morning, models continue to advect cold
air into the Pacific Northwest through Thursday. The big question is
how fast the true arctic air mass can advect southward into the Pac
NW. It should be noted that the models are almost always too fast in
advancing the arctic air. This will be important for when the next
system approaches for Thursday night or Friday. Ensemble guidance is
all over the place in regard to the progression of the arctic air;
for example, there is a bimodal distribution in the LREF Grand
Ensemble low temperatures for PDX Friday night. There are still
members suggesting lows in the single digits, while others suggest
lows in the 40s. There are not many members in the 25-35 deg F range,
but about 60% of members are colder than 25 deg F and about 25% are
warmer than 35 deg F. Based on past experience with arctic air moving
in slower than expected, would hedge a bit more than that toward the
milder minority of solutions. If the arctic air does indeed make it
into the PDX metro by the weekend, there would obviously be
consequences down the road as additional systems approach the Pac NW.

Buckle up and hold on tight...this next week is going to serve up
some interesting and very challenging forecasting. This is the kind
of week where people will want to pay close attention to the weather,
as there will likely be frequent changes to the forecast as models
hone in on the features listed above.  Weagle

&&

.AVIATION...A cold front will push through the region tonight
bringing another round of moderate rain between 06-09z Tue. Expect
predominately MVFR cigs with this frontal passage. After 10-12z
Tue, the region enters a post-frontal environment with showers and
cigs hovering around high-end MVFR/low-end VFR. Through the day
Tuesday, also expect a 20-30% chance of thunderstorms along the
coast and 15-30% chance of thunderstorms in the Willamette Valley.

Southwest winds with gusts of 35-40 kt inland and 40-45 kt along
the coast. Winds will increase to 50 kt aloft around 2000 ft out
of the southwest into Tuesday morning. Winds will slightly weaken
and become westerly behind the front after 12z Tue, but still
potentially gust up to 25-30 kt inland and 30-35 kt at the coast.

PDX AND APPROACHES...Expect high-end IFR/low-end MVFR cigs through
tonight ahead of the front. After 10-12z Tue, cigs should improve
to high- end MVFR/low- end VFR. Early tonight, SW winds increase
with gusts up to 35-40 kt. After 12z Tue, SW winds slowly weaken,
with gusts to around 25-30 kt through the end of the TAF period.
Expect a 15-20% chance of thunderstorms between 15z Tue to 00z
Wed. -BMuhlestein/Alviz

&&

.MARINE...A very active weather pattern continues through the week
as a series of low pressure systems moves across the northeast
Pacific Ocean. Observations as of 2pm PST at buoy 46050 show
southwest winds gusting up to 30 kt with seas between 11-12 feet.
The current Small Craft Advisory for the waters is on track and
is expected to drop off this evening before the next storm system
arrives.

A cold front will push through the waters tonight into early
tomorrow morning (Tuesday), associated with a 980 mb low pressure
system off the coast of British Columbia near Queen Charlotte
Sound. This will bring strong west-southwest Gales with gusts up
to 40 to 45 kt. A dominant westerly swell will also push into the
waters Tuesday, buildings seas to the mid to upper 20s (potentially
up to 30 ft), peaking around Tuesday afternoon. Winds may briefly
weaken with gusts of 25 to 30 kt early Tuesday afternoon before
the next system arrives.

Tuesday evening into early Wednesday morning, a 1000-1005 mb low
pressure system will move through the waters from the west
northwest, returning Gales with northwest gusts up to 35 to 40 kt
(isolated gusts up to 45 kt possible). Seas will slowly subside,
but remain elevated at around the upper teens to low 20s. After
mid-morning Wednesday, winds are forecast weaken to high-end
small craft (gusts up to 30 kt) and seas will gradually falling
to the low to mid teens through at least Thursday morning. See
the beach hazards section for more info on the high surf and
coastal flooding potential.	  -Alviz

&&

.BEACH HAZARDS...A dominant westerly swell will move through the
waters early Tuesday morning, with seas building up to 25 to 30
ft throughout the day Tuesday. Seas will slowly subside to around
18 to 22 ft late Tuesday night into Wednesday morning. Therefore,
a High Surf Warning remains in effect beginning early Tuesday
morning through at least Wednesday afternoon. Breaker heights up
to 35 ft are possible along the south Washington coast and 29 to
33 ft along the north and central Oregon coast. Higher than normal
water run-up is expected on beaches and low-lying shorelines.

In addition, the high tide at Toke Point, WA is forecast at 11.2
ft around 10-11 am PST Tuesday. In conjunction with the high surf,
this will lead to the potential for tidal overflow flooding.
Thus, a Coastal Flood Advisory has been issued for the south
Washington coast from early Tuesday morning to early Tuesday
afternoon. Currently, the highest tides for the north and central
Oregon coast are forecast just below tidal overflow criteria.
Will monitor the potential for coastal flooding through the
remainder of the week, especially with Perigean Spring Tides
expected late in the week.	  -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Wind Warning until 4 PM PST Tuesday for Coast Range of
     Northwest Oregon-North Oregon Coast.

     High Surf Warning from 4 AM Tuesday to 4 PM PST Wednesday for
     Central Oregon Coast-North Oregon Coast.

     Wind Advisory until 6 PM PST Tuesday for Central Willamette
     Valley-Greater Portland Metro Area-Lower Columbia.

     Winter Storm Warning from 4 AM Tuesday to 4 PM PST Wednesday for

     Cascade Foothills in Lane County-Cascades in Lane County-
     Northern Oregon Cascade Foothills-Northern Oregon Cascades-
     Upper Hood River Valley.

     Blizzard Warning from 4 AM Tuesday to 4 PM PST Wednesday for
     Cascades in Lane County-Northern Oregon Cascades.

WA...High Wind Warning until 4 PM PST Tuesday for South Washington
     Coast-Willapa Hills.

     High Surf Warning from 4 AM Tuesday to 4 PM PST Wednesday for
     South Washington Coast.

     Wind Advisory until 6 PM PST Tuesday for Greater Vancouver Area-
     I-5 Corridor in Cowlitz County.

     Winter Storm Warning from 4 AM Tuesday to 4 PM PST Wednesday for

     South Washington Cascade Foothills-South Washington
     Cascades.

     Blizzard Warning from 4 AM Tuesday to 4 PM PST Wednesday for
     South Washington Cascades.

     Coastal Flood Advisory from 7 AM to 2 PM PST Tuesday for South
     Washington Coast.

PZ...Gale Warning until 4 AM PST Wednesday for Coastal waters from
     Cape Shoalwater WA to Florence OR out 10 NM-Columbia River
     Bar-Coastal waters from Cape Shoalwater WA to Florence OR
     from 10 to 60 NM.
&&

&&

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