440
FXUS66 KPDT 050538
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
938 PM PST Tue Feb 4 2025

.UPDATED AVIATION...Flight categories will vary across TAF sites
as the upper level system moves across the PacNW bringing SN,FG
and BR to many sites.

DLS/YKM/PSC are currently VFR. However, PSC/YKM will see periods
of MVFR due to CIGs below 3kft and the probability of snow causing
VIS to drop to 4SM.

PDT/ALW are currently IFR and are expected to vary between IFR and
LIFR as the system continues to bring snow and fog across the TAF
sites. These sites are expected to return to MVFR and VFR later in
the period once the system moves out of the area near 19-21Z.

RDM/BDN are LIFR due to very low CIGs below 400 feet with VIS 5SM
at BDN and mist while RDM has varied between 1/2-1/4SM due to
FZFG. These sites are expected to return to VFR later in the
period near 20-22Z.

Confidence is the forecast is moderate (50-70%) with regards to
the onset and ending of the snow, and high (70-90%) with the
return of VFR conditions later in the period. Bennese/90


&&

.PREV DISCUSSION... /issued 302 PM PST Tue Feb 4 2025/

SHORT TERM...Today through Thursday night...

Key Messages:

1. Moderate to heavy snowfall this evening through Wednesday
   *Winter Weather Warnings and Advisories Issued*

2. Cold, below normal temperatures persist through period.

Current radar and visible satellite imagery showing light returns
extending southwest to northeast across the region, with moderate
returns beginning to develop over elevated terrain and into
Deschutes County under mostly cloudy to cloudy skies. Snow showers
will be intensifying this evening and continuing into Wednesday
morning as significant snow amounts are anticipated, warranting
the issuance of several Winter Storm Warnings and Winter Weather
Advisories. This is in response to the upper level low pressure
system that has been stalled offshore, tapping into sub-tropical
moisture and advecting it into our region. This airmass is quite
moist, allowing for enhanced moisture transport resulting in heavy
snowfall potential. A stationary front has set up along the
Washington/Oregon border due to the elongated stay of the offshore
low pressure system, which will further enhance lift and snowfall
rates as the plume of moisture travels over the area this
evening. A break down of Winter Products are below:

WINTER STORM WARNINGS:

Wallowa County until 10 AM Wednesday with 5 to 10 inches
expected. Confidence in these snow amounts is high (95%) as the
HREF and NBM advertise an 90-100% chance of 5 inches of snow or
more over this timeframe.

John Day-Ochoco Highlands until 10 AM Wednesday with 3 to 5 inches
expected. Confidence in these snow amounts is high (90%) as the
HREF and NBM showcase an 80-100% chance of 3 inches of snow or
more over this timeframe.

Foothills of the Northern Blue Mountains of Oregon and Washington
until 10 AM Wednesday with 3 to 5 inches expected. Confidence in
these snow amounts is high (75%) as the HREF suggests an 80-100%
chance of 3 inches of snowfall, but a 35-55% chance of 3 inches
of snowfall via the NBM.

WINTER WEATHER ADVISORIES:

East slopes of the Oregon Cascades above 4000 feet until 4 AM
Thursday as 3 to 7 inches of snow is expected. Confidence in these
amounts is high (95%) as the HREF and NBM suggest an 85-100%
chance of 3 inches of snow or more over this timeframe.

Northern and Southern Blue Mountains until 10 AM Wednesday as 4 to
6 inches of snowfall is expected. Confidence in these snow amounts
is high (90%) as both the HREF and NBM suggest an 80-100% chance
of 4 inches of snowfall or more over this timeframe.

Lower Columbia Basin of Oregon until 10 AM Wednesday with 2 to 4
inches expected. Confidence in these snow amounts is high (75%) as
the HREF highlights a 70-80% chance of 2 inches of snowfall or
more, but the NBM suggests only a 50-60% chance.

John Day Basin, Southern Blue Mountain foothills of Oregon, and
Central Oregon until 10 AM as up to 4 inches will be possible.
Confidence in these snow amounts is high (80%) as both the HREF
and NBM suggest a 70-90% chance of 2 inches or more of snow,
dropping to a 40-60% chance when increasing to 3 inches or more.

Grande Ronde Valley until 10 AM Wednesday with 3 to 6 inches of
snowfall anticipated. Confidence in these amounts is moderate to
high (70%) as the HREF captures a 100% chance of 3 inches or more,
but the NBM captures very little chances (<20%) of occurrence.

The system offshore has brought cooler than normal temperatures
across the region as high temperatures today have struggled to
reach above freezing. Temperatures tonight are expected to be the
coldest in the forecast as Wednesday morning lows will drop into
the mid-to upper teens across the Blue Mountain foothills and
Central Oregon, and upper teens to low 20s over lower elevations
of the Basin. These values are 8-12 degrees below normal for this
time of year. Flow aloft will turn more from the southwest into
Wednesday, allowing temperatures to warm slightly as highs break
into the mid-to upper 30s across lower elevations. This looks to
change to the northwest into Thursday, dropping highs back in the
low to mid-30s. 75


LONG TERM...Friday through Tuesday...

1) Chance of area wide light snow through the extended.
2) Low temperatures drop to upper-teens to low-20s
3) Winds remain light and variable.

The extended period will begin with a shortwave upper-level trough
pushing onshore of the PacNW. SW flow will inject moisture into the
CWA, increasing chances for light snow on Friday for all areas.
Models are in good agreement that some form of measurable snow (>0.1
inches) is likely area wide, although QPF amounts remain low and
insignificant. According to the NBM, lowland snow chances are mostly
restricted for the Lower Columbia Basin, including the Ochoco-John
Day Highlands (20-50% chance). Higher elevations in the Mountains
will be greater at 40-80%.

The trough will exit the region by early Saturday morning, with a
ridge building right behind the trough. The area will sit on the
leeward side of the ridge for the remainder of the period bringing
in dry/cool NW flow. Precip chances will not be as great going
forward with this set-up, with light snow chances tapering off to
the higher elevations.

Temperatures will generally be in the mid to high 30s, dropping to
the mid-20s to low-30s by Tuesday. This is a -10 to -15 degree below
normal difference through the extended. Lows overnight will be in
the mid teens to low 20s, with some areas (especially central OR and
the Eastern Mountains) getting down to the single digits. Winds will
remain light and variable at 5-10 kts in most places.



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  16  36  20  30 /  80  20  30  20
ALW  18  36  22  32 /  90  40  30  30
PSC  21  38  22  35 /  70  10  20  10
YKM  17  34  19  35 /  30  20  20  10
HRI  20  39  22  34 /  70  20  20  20
ELN  15  31  15  30 /  20  30  30  10
RDM  13  34  18  32 /  60  40  40  20
LGD  16  35  20  35 /  90  30  40  30
GCD  18  35  20  36 /  90  20  40  30
DLS  23  39  25  35 /  50  60  40  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST Wednesday for ORZ044-049-
     502-503-505-508-511.

     Winter Storm Warning until 10 AM PST Wednesday for ORZ050-506-
     507.

     Winter Weather Advisory until 4 AM PST Thursday for ORZ509.

WA...Winter Weather Advisory until 10 AM PST Wednesday for WAZ030.

     Winter Storm Warning until 10 AM PST Wednesday for WAZ029.

&&

$$

SHORT TERM...75
LONG TERM....95
AVIATION...90