Blizzard and Winter Storm in Washington, January 11 to 13, 2024

Area Forecast Discussion
National Weather Service Portland OR
432 AM PST Thu Jan 11 2024

.SYNOPSIS...Cold northwest flow aloft will promote showery
conditions through Thursday night, with snow amounts increasing
again across the Cascades Thursday into Friday. An arriving
arctic air mass Friday into Saturday brings fresh snow concerns
to the Coast Range and Willapa Hills and the lowlands of far
northern Oregon including the Gorge and Portland metro as well
as freezing rain concerns for the central and southern
Willamette Valley, southern Coast Range, and Oregon and SW
Washington coast. Precipitation ends by early Sunday, with
frigid conditions lingering over the region through early next
week.

&&

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT...Showers continue
across NW Oregon and SW Washington early Thursday morning, as
depicted on radar imagery. Showery conditions with light
accumulation will continue through tonight as northwest flow
persists over the region, with snow levels generally holding
steady around 1500 feet. It is possible that any stronger
showers may be able to briefly pull snow levels down closer to
the valley floor into this morning or tonight via dynamic
cooling processes, but temperatures in the mid 30s should
inhibit any accumulation on surfaces. Therefore do not
anticipate any significant winter weather issues in the lowlands
through tonight. Have issued a Winter Storm Warning for the
Cascades above 1500 feet as snow amounts will start to increase
again today as the next embedded trough starts to drop down
from the north. While snow amounts may not meet strict warning
criteria in any one 12 hour period over the next few days,
nearly continuous snow will add up to around 2 feet below the
passes and 2 to 4 feet for the passes and above through Saturday
afternoon.

The main focus of the next few days is the lowland winter
precipitation potential Friday into Saturday. Ensemble guidance
continues to indicate an arctic mass will push into the PacNW
from the east as a stronger weather system moves into the region
from the west. Latest ensemble and NBM guidance indicates high
confidence in the arctic mass pushing into central Oregon,
though some uncertainty remains into just how far south the
coldest temperatures will be. The 75th percentile from the 07z
NBM run keeps high temperatures in the 20s for the Portland
metro area and the 20s to low 30s as far south as Eugene.
Confidence continues to increase in a mix of wintery
precipitation across almost the entire forecast area Friday into
Saturday, though uncertainty still remains on the amounts and
type of wintery precipitation for portions of the area.

In terms of the track of the incoming low pressure system, the
last two GFS runs (00z and 06z Thursday) have begun nudging
closer to the more southern Euro and NAM tracks, as have the
majority of GEFS and Euro ensemble members. The tracks are not
exactly the same, but they trend to the low moving somewhere
into central Oregon instead of closer to the Oregon/Washington
border as previous GFS runs had. In turn, this increasing
consensus in guidance has shifted the bulk of precipitation
falling Friday into Saturday more south into central to southern
Oregon, which has reduced QPF amounts significantly across NW
Oregon and SW Washington, especially for areas north of a line
generally from southern Tillamook County to central Clackamas
county. Where 48 hour QPF totals from the forecast 24
hours ago were around 2-3 inches across the Willamette Valley
and lowlands of SW Washington, the latest forecast indicates
only 0.25-0.5 inch for the Portland metro area and north,
0.50-1.25 inch for the central Willamette Valley, and 1.5-2.25
for the southern Willamette Valley. This, of course, will then
impact the total amount of wintery precipitation that could
fall. Some uncertainty in the final track of this low still
remains, so we expect forecast QPF and wintery precipitation
amounts to fluctuate as we get closer to the event.

In terms of precipitation type, confidence is increasing on
this, as well. Latest runs of the LREF, HREF, and NBM all
indicate increasing potential for freezing rain late Friday
night into Saturday across the central and southern Willamette
Valley, the southern Coast Range, and the coast from central
Oregon to SW Washington. NBM indicates a 15-25% probability of
at least 0.1 inch of freezing rain for locations near and south
of Eugene, the southern Coast Range, and the Oregon coast around
and south of Tillamook. Additionally, there's a 40-70%
probability of any freezing rain for the same locations and a
15-25% probability of any freezing rain for locations around
Salem and the far northern Oregon coast into the SW Washington
coast. If any snow falls in these areas, temperatures may be too
warm for snow to stick.

Additionally, these models indicate precipitation will likely
fall as snow in the northern Willamette Valley into SW
Washington, though soundings do still show a notch of warm air
above 3000 feet that could allow some sleet to mix in,
especially in the earlier hours of snow. Probability of 1+ inch
of snow ranging from the lowlands of Cowlitz County, WA down to
the Salem area, including the Portland/Vancouver metro area,
are around 50-65% with a 40-50% probability down to the
Corvallis area. Probabilities for 4+ inch of snow for the same
areas have decreased to 25-40% and 0% respectively due to more
ensemble members lowering QPF in these areas.

There is also high confidence in easterly winds returning to
the Columbia River Gorge Friday evening into this weekend as
the TTD-DLS pressure gradient reaches an impressive -10 mb. This
would support 50 to 60 mph gusts through the western Gorge and
even higher gusts in favored locations such as Crown Point and
Corbett. Given the snow potential in the forecast, this points
to the strong possibility for blizzard conditions through the
Gorge Friday night into Saturday if the snowier solutions come
to fruition. Opted to issues Winter Storm Watches for each of
the areas discussed above given potential for significant
lowland winter weather impacts. Bottom line, stay tuned to the
forecast in the coming days as this remains a fluid situation
with several plausible outcomes still on the table. -CB/HEC

.LONG TERM...SUNDAY THROUGH WEDNESDAY...Guidance indicates
precipitation tapering off across the area by Sunday morning at
the latest, with mostly dry conditions likely through Tuesday as
ensemble clusters remain in strong agreement on ridging
developing over the region early next week. This will make cold
temperatures the primary forecast concern from Sunday through
Tuesday, with highs remaining below freezing in the lowlands and
overnight lows dropping into the teens. Winds will persist
through the Gorge, possibly bringing wind chills into the low
single digits in eastern parts of the metro through early next
week. Temperatures look to begin to moderate by the middle of
next week as onshore flow slowly returns and a weather system
approaches the region. -CB/HEC

&&

.AVIATION...Showers within northwesterly flow continue across the
area and will do so over the next 24 hours. Minimal changes
through the forecast as the main category changer will be CIGs.
CIGs will be a bit more variable bouncing around between high end
MVFR and low end VFR. Showers will increase in intensity around
20Z (from west to east) which will drop conditions to MVFR. While
some pockets of lower clouds are present, not necessarily looking
at them being predominate. Some breezier winds along the coast,
but in general winds remain northwesterly under 10 kt. Will see a
similar trend over the forecast. As a quick note, weather will
become much more active starting on Friday with the potential for
impactful winter weather. For more details, please read the long
term discussion portion of the area forecast discussion.

PDX AND APPROACHES...Minimal impact. Showers will persist,
intensifying around 22Z, though will not be "moderate". During
this period of heavier rain, CIGs will lower to MVFR. Temperatures
will hover right around freezing towards the end of the forecast
period. -Muessle

&&

.MARINE...Northwesterly winds will prevail through Thursday around
20 to 25 kt. Gusts up to 30 kt are likely. Seas, currently at 14
ft at 12 seconds at buoy 46050 will continue to ease through the
next 48 hours finally reaching 9 ft Saturday morning. Will
maintain the Hazardous Seas Warning through this period, but will
transition to a Small Craft Advisory late this morning.

Friday, a low pressure system will push through the waters. Winds
are likely to gust to high-end small craft/low-end Gales (30-35
kt) with an initial onshore component. However, winds turn more
easterly over the weekend as pressure gradients increase. The
easterly winds will counter act the westerly swell so not
expecting exceptionally high wave heights. However, around the
Columbia River Bar, and the coastal gaps, could see the higher end
winds of that range. Peak winds will occur on Saturday morning.
												-Muessle/Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Storm Watch from Friday afternoon through late Saturday
     night for Cascade Foothills in Lane County-Central Coast
     Range of Western Oregon-Central Oregon Coast-Central
     Willamette Valley-Coast Range of Northwest Oregon-Greater
     Portland Metro Area-Lower Columbia-North Oregon Coast-
     Northern Oregon Cascade Foothills-South Willamette Valley-
     Western Columbia River Gorge.

     Winter Storm Warning until 4 AM PST Sunday for Cascade Foothills
     in Lane County-Cascades in Lane County-Northern Oregon
     Cascade Foothills-Northern Oregon Cascades.

     Winter Storm Watch from Friday morning through late Saturday
     night for Central Columbia River Gorge-Upper Hood River
     Valley.

WA...Winter Storm Watch from Friday afternoon through late Saturday
     night for Greater Vancouver Area-I-5 Corridor in Cowlitz
     County-South Washington Cascade Foothills-South Washington
     Coast-Western Columbia River Gorge-Willapa Hills.

     Winter Storm Warning until 4 AM PST Sunday for South Washington
     Cascade Foothills-South Washington Cascades.

     Winter Storm Watch from Friday morning through late Saturday
     night for Central Columbia River Gorge.

PZ...Hazardous Seas Warning until 10 AM PST this morning 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.

     Small Craft Advisory from 10 AM this morning to 4 AM PST Friday
     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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