Cold in Oregon, February 2, 2025

Area Forecast Discussion
National Weather Service Portland OR
947 PM PST Sat Feb 1 2025

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
Lowland rain showers and mountain snow showers will
continue this afternoon. Significant accumulations in the
mountains which will lead to hazardous travel conditions.
Tonight, more of the lowlands will start to see a rain/snow
mix, with little to no accumulation expected. This trend
continues into next week, with much colder temperatures.

&&

.SHORT TERM...Now through Sunday night... Radar and satellite
imagery as of 230 PM PST Saturday depicts broken cloud cover and
scattered showers across northwest Oregon and southwest
Washington as the area briefly remains in zonal flow aloft.
Tonight into Sunday, a deep, cold trough will begin to trek
southward from British Columbia with its axis centered just
offshore of the Pacific Northwest. Colder air from this trough
will lead to snow levels falling to around 500 feet or less
tonight across southwest Washington and far northwest Oregon.
Meanwhile, snow levels south of Lincoln City - Salem are
forecast to remain above 500-1000 feet.

Given these lower snow levels, a rain/snow shower mix is
possible down to the valley floor tonight (especially the
further north you go). Since overnight temperatures will hover
around freezing (32F), a slight increase or decrease in
temperatures could lead to an all-rain or all-snow scenario. In
addition, the showery nature of the precipitation will lead to
varying rain and snow amounts across the area. Those that
experience heavier showers could end up with cooler temperature
via wet-bulbing, and thus receive more snow than others. If any
accumulation occurs below 500 feet, it would likely be on grassy
areas and elevated surfaces and road temperatures will be too
warm. Therefore, expect limited impacts to travel in the
lowlands. Any lowland snow accumulations are expected to melt
during the day tomorrow as temperatures warm into the low 40s.

The Winter Storm Warnings for the Cascades, north Oregon Coast
Range, and Willapa Hills remain in effect through at least 4 AM
tonight. New hazard additions include Winter Weather Advisories
for the Willapa/Wahkiakum lowlands, Cowlitz County lowlands,
Upper Hood River Valley, and Lane County Cascade foothills from
4 AM Sunday to 4 AM Monday. If you plan to travel through the
coastal mountains or Cascades, prepare for winter weather
and refer to ODOT/WSDOT for the latest road conditions and
restrictions. For forecast snow amounts, reference the posted
hazard headlines and/or the point-and-click forecast.

Lowland rain and mountain snow showers will continue throughout
the day Sunday, with Sunday night forecast colder than tonight
as the aforementioned trough dips further south. As a result,
snow levels fall even lower across the entire area, around 0-200
feet. Rather than a rain/snow mix in the lowlands, we could see
just pure snow showers Sunday night, even along the coast.
Accumulations are still minimal and are not expected to cause
significant travel impacts. But will note that snow that melts
during the day may re-freeze over night and lead to slippery
surfaces.      -Alviz

.LONG TERM...Monday through Friday...WPC clusters are in
general agreement the deep, upper level troughing remaining in
place just offshore of the Pacific Northwest in the long term
forecast. This will bring much-below normal temperatures for
this time year, with high temps across the interior lowlands
currently forecast in the upper 30s and lows forecast in the mid
to upper 20s by early to mid next week. The coldest scenario
(10% chance) has lows dropping into the upper teens and low 20s.
This trough will also support continuous shower activity,
including snow showers to the valley floor as snow levels
generally remain around 500 feet or less through the middle of
next week.

Of course, there remains uncertainty with where showers will
set-up, but at this time a significant snowfall event for the
lowlands below 500 feet looks unlikely. The current probability
for snowfall exceeding 3 inches (warning-level) for the lowlands
is around 10-20% through early to mid next week. The broad onshore
flow regime in place makes it harder for significant lowland
snow, however, the upper level trough dipping down is bring air
that's just cold enough to at least support a rain/snow mix or
light snow showers.

That being said, expect minimal accumulation of snow for
elevations below 500 feet; generally limited to grassy areas
and elevated surfaces. Similar messaging in the short term
discussion: any snow that does accumulate on any given day below
500 feet will occur during the overnight/morning hours, with
melting of snow by the afternoon as we warm up. However, with
temperatures falling to near or below freezing each night, re-
freezing of wet surfaces will lead to slippery surfaces. In
addition, anyone traveling over the mountains (Cascades/Coast
Range) should continue to monitor the forecast and refer to
ODOT/WSDOT for road conditions and travel restrictions.
-Alviz

&&

.AVIATION...Post frontal showers will continue through the TAF
period with primarily VFR conditions outside of brief drops to
MVFR under locally moderate shower activity. As temperatures drop
later tonight into Sunday morning due to a colder airmass moving
in overhead, we may see some snow mixing into rain showers at
times after around 12z Sun or so. The latest high resolution
ensemble guidance puts chance of rain/snow mix at 30-40% for
almost all terminals (slightly lower chance at the coast near KONP
and KUAO/KSLE southward). No accumulation is anticipated on
pavement surfaces with a trend back to just rain showers Sunday
afternoon; any additional rain/snow mix will intensity dependent.
Winds generally remain 5 to 10 knots or less.

.PDX AND APPROACHES...Rain showers continue across the area
with predominantly VFR conditions expected at the terminal but
with a 20-30% chance for MVFR CIGs/VIS at any given time during
the TAF period should showers pass directly overhead. After 12z
Sun, cooler temperatures aloft will allow for some snowflakes to
mix in with rain through Sunday afternoon although if a shower
remains light enough the precipitation will most likely stay as
rain. No accumulation anticipated; ~10% chance of temporary
light slushy accumulation on the grass if a heavy shower passes
overhead. -Schuldt/JLiu

&&

.MARINE...A broad area of low pressure centered near Vancouver
Island maintains blustery conditions through the end of the day,
with west winds gusting to 20-25 kt and seas lingering in the
10-12 ft range. Marginal Small Craft winds in the central and
northern waters, and the Advisory continues through Sunday
morning. SCA out for the Columbia River Bar as well through
Saturday evening, primarily for a stronger ebb current in the
evening. From Sunday onwards, wind gusts come down to under 15
kt as broad low pressure sinks southward towards the region and
relaxes surface pressure gradients. Conditions will remain
fairly benign through at least the middle of next week. /CB/JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday
     for ORZ104-121-125.
     Winter Storm Warning until 4 AM PST Monday for ORZ106.
     Winter Weather Advisory until 4 AM PST Monday for ORZ119-123-
     124.
     Winter Storm Warning until 4 AM PST Sunday for ORZ126>128.
WA...Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday
     for WAZ202-204.
     Winter Storm Warning until 4 AM PST Monday for WAZ203.
     Winter Weather Advisory until 4 AM PST Monday for WAZ208.
     Winter Storm Warning until 4 AM PST Sunday for WAZ211.
PZ...Small Craft Advisory until 10 PM PST this evening for PZZ210.
     Small Craft Advisory until 6 AM PST Sunday for PZZ251-252-271-
     272.
&&

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