208
FXUS66 KPQR 072327
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
327 PM PST Fri Feb 7 2025

.SYNOPSIS...The two main periods of focus for winter weather
impacts across the region continue to be tonight into Saturday
morning, and the middle of next week, as temperatures likely
stay below normal through the middle of February. While some
uncertainty remains across the low elevations for snowfall
potential come Saturday morning, (impacts likely above ~800ft)
there is growing concern for a larger-scale winter weather event
Feb 12-14. Confidence is sill low in regards to the exact
precipitation type, amounts, and timing, but the proverbial
alarm-bells are beginning to go off given the favorable
synoptic setup and slowly increasing model agreement during
this latter time period.

&&

.SHORT TERM...Now through Sunday night...Going through Saturday
all eyes are on our next weather disturbance in the form of an
upper-level shortwave trough clearly seen on visible satellite
imagery late this afternoon. Skies will gradually become
cloudier this evening as the aforementioned feature approaches
however some guidance, including the NBM, are not resolving the
gaps in cloud cover seen on visible satellite proceeding the
main precipitation band; this will be important as we attempt to
radiationally cool post-sunset. Dew-points have also been
running a degree or two lower than expected this afternoon too,
which bodes well for dynamic cooling to punch snow-levels
towards surface once precipitation arrives overnight should the
current trend hold, not to mention increasing weak offshore
flow will work to advect slight cooler/drier air through the
Gorge overnight too. These are just a few of the facets
involved in what is honestly a tricky and marginal lowland
snowfall forecast headed into Saturday morning.

So all in all, will the I-5 corridor including the
Portland/Vancouver metro see snow come sunrise Saturday morning?
Well at this point confidence is high well see at least some snow
in the air between midnight and 8am, but accumulations beyond
just a slushy dusting are mostly likely confined above 500-800ft
and in the immediate Columbia River Gorge. Temperatures,
especially pavement temperatures, for locations lower than
500-800ft will just be too warm to support widespread snowfall
impacts. That said, there does remain an outside chance (10-20%)
snowfall amounts overperform beyond the current forecast and a
few isolated locations below 500ft see ~1-2 inches of wet
snowfall (mainly in the grass), but attempting to target the
isolated spots where(or even if) this occurs is an effort in
futility until the precipitation starts to fall. Such is the
nature of this marginal set-up. Given the current trend and the
latest expected snowfall amounts tonight and Saturday morning,
have opted to issue a Winter Weather Advisory for the Coast
Range, West Hills/Chehalem Mountains, Cascade foothills, outer
southeast Portland Metro(above 500ft) and the Columbia river
Gorge. We will be keeping a very close watch on how conditions
continue to trend this evening.


Headed through the the second half of Saturday morning into the
afternoon temperatures rise into the 40s across the lowlands thus
ending showery snowfall impacts below 1000-1500ft. Conditions
then trend drier Saturday night through Sunday night aside from
lingering showers near the coast and snow showers in the
coastal mountains and Cascades (30-50% chance). Precip chances
are only around 10-15% in the Willamette Valley from Portland to
Eugene. With some additional partial clearing overnight
temperatures stay chilly both nights, however, not cold enough
to justify a cold weather advisory as most lowland locations
will see overnight lows in the upper 20s to near 30 with calm
winds - patchy fog in combination with the below freezing
temperatures will be a concern. Offshore winds do look to
develop Sunday night, which will eventually bring colder
temperatures into the region. This is discussed further in the
long term discussion.  -Schuldt


.LONG TERM...Monday through Friday...Going through next week
the long term forecast continues highlight abnormally cold
temperatures and slowly growing confidence in the potential for
snow, sleet and/or freezing rain down to the valley floor in the
Wednesday through Friday time period. Come Monday into Monday
night nearly 100% of the latest ensemble guidance from the
ENS/GEFS/GEPS show the development and/or continuation of low-
level offshore flow and increasing east winds through the
Columbia River Gorge and eastern Portland/Vancouver metro.
Thisll be aided by the traversal of a heavily tilted upper-
level shortwave racing southward from Canada early next week,
opening the door for arctic air to spill southward into eastern
WA/OR by Tuesday, eventually advecting westward.

As such, abnormally cold temperatures are anticipated Monday
through Thursday, coldest during the overnight and morning hours
when widespread lows in the mid teens to mid 20s are likely to
occur for the inland valleys. The latest NBM continues to show a
70 to 90% chance for low temps below 25 degrees from the coast
to the Cascades Tuesday night into Wednesday morning, which
appears to be the coldest period. There is a 20-50% chance for
lows below 20 degrees, except 60-90% in Eugene, Tillamook,
Battle Ground, Vernonia, Sweet Home, and other outlying rural
areas generally within the Willamette Valley. The high Cascades
will likely see low temps in the single digits. This means there
is a high chance cold weather advisories will need to be issued
as we get closer to next week with the increasing risk of cold
weather impacts. High temps will likely struggle to climb out of
the 30s to near 40 across the lowlands Tuesday through Thursday
as well.

Once the cold air attempts to lock in place next week, we will
need to watch closely for potential wintry precipitation,
especially late Wednesday through Friday, when a vast majority
of ensemble guidance shows incoming precipitation and NBM
6-hourly PoPs increase to 60-80%. It appears the incoming
precipitation will be in response to a broad surface low over
the northeast Pacific with an associated frontal system moving
towards the coast. Ensemble guidance still depict a decent
amounts of spread in the strength and track of this feature
placing it as far north as Vancouver Island or as far south a
Northern California. Its worth noting both the ensemble means
for the GEFS and EPS do bring this low pressure right into the
north Oregon coast, a pattern conducive to winter weather for
much of the area. In the end the exact route this surface low
takes will dictate our impacts regionally. If this low tracks
near or just to the south of Astoria (current ensemble mean),
there will be a high likelihood for a winter storm across
southwest WA and northwest OR due to snow, sleet and/or freezing
rain - also dependent on the location and proximity to the warm
front associated with this low. If this low tracks well north
of Astoria towards say the Olympic Peninsula, precipitation
would more likely fall as rain for the coast and Willamette
valley with a wintry mix in the Portland Metro, sheltered
Cascade Valleys, and Columbia River Gorge at least to start
before winds quickly switch southerly at the surface bring in
warmer temperatures thus limiting the scope of impacts. For now,
the forecast is worth monitoring over the coming days to see
how incoming guidance trends towards a firmer solution, especially
if you have upcoming travel plans next week. -Schuldt/TK



&&

.AVIATION...Westerly flow aloft as a broad trough remains over the
region. Predominately VFR expected through this evening with
increasing clouds. The next low pressure system will approach the
area overnight bringing scattered rain and snow showers. CIGs
also are expected to lower, with MVFR conditions likely after 06z
Saturday at the coast, and after 10z across the interior valleys.
Light southerly winds expected to persist through tonight.

PDX AND APPROACHES...VFR with cigs around 4000-5000 ft expected
through this evening. Clouds increase tonight ahead of a weak low
pressure system that will bring rain/snow showers after midnight.
Greater than 70% chance that cigs drop to MVFR (1500-2500 ft)
after 10z Sat. Southerly winds expected around 4-6 kt, becoming
southeasterly tonight. /DH

&&

.MARINE...A relatively weak low pressure system will move across
the coastal water tonight. Southerly winds continue to increase
today with gusts up to 20-25 kt for about a 6 hour period
overnight. Have issued a Small Craft Advisory for all coastal
waters later this evening through 4 am Saturday. Seas will remain
predominately wind driven, building to around 5 to 6 ft.
Conditions through the weekend and into early next week are
expected to be relatively benign as high pressure persists
offshore with northerly winds and seas around 4 to 6 ft. As the
high pressure over the waters beings to weaken, offshore flow is
expected to increase Tuesday into Wednesday next week. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 10 PM this evening to noon PST
     Saturday for ORZ106-107-110-113-119-120-123>125.
WA...Winter Weather Advisory from 10 PM this evening to noon PST
     Saturday for WAZ203-208-209.
PZ...Small Craft Advisory from 8 PM this evening to 4 AM PST
     Saturday for PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

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