Heavy Snow in Oregon, February 28 to 29, 2024

Area Forecast Discussion
National Weather Service Pendleton OR
208 PM PST Wed Feb 28 2024

.SHORT TERM...Today through Friday...The much-advertised cold front
is now upon us as winds have started to pick up across the forecast
area this afternoon. With a predominately SW to S direction, areas
lying at the northern base of a E/W mountain range are most at risk
of seeing strong winds. Obs in areas such as Yakima and Cabbage Hill
have confirmed this, with both reporting gusts approaching or even
exceeding 60 mph. The strongest winds of the period are yet to occur
as well, with the true arrival of the cold front overnight promising
more widespread gusts over 45 mph. Wind advisories remain in effect
across much of the forecast area, with windy conditions expected to
prevail until early evening Thursday.

This increase in winds, brought about by amplified SW flow aloft, has
allowed robust warm air advection to take place across the CWA as
well. Already seeing widespread 50s across our population centers
this afternoon, with even our mountain passes recording mid 30s
after a night of snowy conditions. Rain has been observed across our
mountain passes as a result, however once cold air surges in behind
the front, snow levels are expected to drop down into the 1500-2000
ft range, allowing for another round of heavy mountain snow and even
some light snow showers across some of our lower elevation zones.
QPF has trended downward a bit compared to previous runs, and am a
bit skeptical as to how efficient snow will accumulate given the
warmer conditions experienced during the day today, however
impactful snowfall is still anticipated for our mountain passes as
the cold front supports locally heavy snowfall rates at times
through early morning Thursday. Precip along the front will extend
into our lower elevations, primarily in the form of rain, however
central and north central Oregon may receive some light snow showers
early morning Thursday. Some hi-res guidance are a bit more
aggressive on precip amounts along the front, but decided to trend
away from these more bullish amounts based on ensemble guidance
favoring more modest numbers. Still, wouldn't be surprised if
central Oregon receives up to an inch of snow in some spots.

The forecast area then becomes enveloped by the trough associated
with the cold front by the latter half of Thursday into Friday.
While moisture will be limited, the sheer amount of lift under the
trough axis will support some light, convective snow showers at
times for the area, mainly above 3000 feet. Not anticipating
accumulations more than a few inches outside of perhaps the highest
mountain crests, but temps will drop down into the 20s and 30s early
Friday morning, and struggle to warm above 50 for even the lowest
elevations in light of cold air filtering in behind the front. Did
add mention of snow/rain showers for the period rather than
stratiform, as the ongoing pattern supports more convective-driven
precip given the oncoming front and the subsequent trough overhead.
Evans/74

.LONG TERM...Saturday through Wednesday...Ensemble and
deterministic models are in excellent agreement that a cold upper-
level low centered just offshore on Saturday will weaken to an open
wave through Sunday over the PacNW. Uncertainty in the 500 mb
pattern grows Monday through Wednesday, though ensemble clusters are
suggesting a very high chance (>90%) that near- to below-normal 500
mb heights will remain over the PacNW during the period.

With the upper-low/trough overhead Saturday and Sunday, showery
weather is forecast - rain/snow for the lower elevations and snow
for the mountains. While confidence is low in any thunderstorms (10%
chance or less), deterministic guidance is advertising some weak
(500 J/kg or less) MUCAPE coupled with steep low/mid-level lapse
rates.

The ECMWF EFI for snow does highlight portions of the Blue Mountains
and Wallowa County with values of 0.5-0.8 on Saturday. Otherwise,
there is low confidence in any climatologically unusual
precipitation, snow, or wind through the period. Plunkett/86

&&

.AVIATION...00Z TAFs...Predominantly VFR conditions are forecast
through the remainder of the day with CIGs of BKN-OVC at 050-100.
South to southwest winds (except VRB06KT at DLS) of 10-25kts with
gusts of 15-40 kts are anticipated through much of the evening and
into the overnight period ahead of a strong cold frontal passage
overnight through Thursday morning. Precipitation will be limited
east of the Cascades today, though confidence is high (70-100%
chance) in some -RA (PDT/ALW/DLS/PSC/YKM) and -RASN or -SN (BDN/RDM)
towards Thursday morning with frontal passage. Brief MVFR CIGs are
forecast for BDN/RDM with -RASN or -SN Thursday morning.
Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  52  31  48 /  40  90  20  20
ALW  40  52  33  49 /  70  90  30  40
PSC  44  54  35  52 /  40  60   0  10
YKM  37  50  28  47 /  60  20  10  20
HRI  41  55  34  53 /  30  80  10  10
ELN  34  45  26  42 /  60  20  10  20
RDM  34  45  27  41 /  50  90  30  30
LGD  39  48  28  44 /  40 100  50  40
GCD  40  50  27  42 /  30  90  40  40
DLS  39  48  32  48 /  90  70  40  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 4 PM PST Thursday for ORZ049.

     Wind Advisory from 1 AM to 4 PM PST Thursday for ORZ050.

     Winter Storm Warning until 4 PM PST Thursday for ORZ502.

     Wind Advisory from 7 PM this evening to 4 PM PST Thursday for
     ORZ505.

     Wind Advisory from 7 PM this evening to 9 AM PST Thursday for
     ORZ507.

     Wind Advisory until 7 AM PST Thursday for ORZ508-510-511.

     Winter Storm Warning until 4 AM PST Friday for ORZ509.

WA...Winter Storm Warning until 4 PM PST Thursday for WAZ030-522.

     Wind Advisory from 7 PM this evening to 9 AM PST Thursday for
     WAZ029.

     Wind Advisory until 7 AM PST Thursday for WAZ027-028-521.

&&

SHORT TERM...74
LONG TERM....86
AVIATION...86