High Wind in Oregon, December 23 to 24, 2024

Area Forecast Discussion
National Weather Service Pendleton OR
245 PM PST Mon Dec 23 2024

.SHORT TERM...Today through Christmas Day...Today marks a respite
amidst an otherwise active weather pattern expected for the next
week. Generally dry and quiet conditions prevail as we transition in
between systems, save for dense fog persisting around the lower
Yakima Valley and Kittitas Valley. By this evening, however, a warm
front will lift through the PacNW and bring yet another round of
precipitation to the forecast area. Models time this precip at
around 7-8 pm tonight in central Oregon, before a deformation band
sweeps across the CWA starting early Tuesday morning. Snow levels
are expected to remain high what with the warm air advecting in
ahead of this system, peaking at 4000 feet for the WA Cascades and
around 7000 feet for the OR Cascades, before cooler air filters in
behind the aforementioned front. Our major mountain passes could see
light accumulating snow through tomorrow afternoon, but given how
warm the weather currently is, confidence is low (<30%) in anything
over an inch or two, with Santiam Pass seeing the best chance at
anything over 2 inches.

As this front lifts through overnight, winds will intensify through
the Grande Ronde Valley and along the base of the Blue Mountains.
Think that current Wind Advisories in effect look good, as pressure
gradient forecasts generally suggest an advisory-level event rather
than High Winds, save for Cabbage Hill where a Warning is in effect.
This pattern is typical for gusty winds through the aforementioned
areas, but thus far guidance doesn't suggest a particularly severe
event. Still, expect gusts across the advised areas to approach and
even eclipse 50 mph.

Late Tuesday night through most of Christmas Day looks quiet until
yet another system in the form of an upper-level trough sweeps
through Christmas night into Thursday. The SW flow aloft leading
this system will once again keep snow levels elevated, at around
3000 feet for the WA Cascades, 4500 feet for the OR Cascades, and
3500-4000 feet for the eastern mountains. While this system does
look to be particularly wet, current thinking is that snow levels
are too high to justify Watches, although will likely issue at least
a Winter Weather Advisory for the WA Cascades when the time comes
given holiday travel. Expect meager snowfall across most of our
mountain passes, save for White Pass which could see (50-60%
confidence) advisory-level snow of at least 6 inches. Below the
aforementioned elevations, expect rain, as part of what will be a
continuous series of rain chances expected through at least next
week. Evans/74

.LONG TERM...Thursday through Monday...The long term will be a
very active period as daily precipitation in the form of mountain
snow and low elevation rain alongside gusty winds is expected as
multiple systems train across our area, tapping into atmospheric
river conditions and producing some river rises while keeping our
mountain snowpack healthily stocked.

Flow with these systems will generally be zonal to southwesterly,
and as each one moves across almost daily during the long term
period, high temperatures are expected to remain in the 40's to
low 50's across our population centers, with overnight lows mostly
above freezing until Sunday night. With these warmer than normal
temperatures, this will keep snow levels between 4-6k feet,
meaning that the bulk of the precipitation that falls will be
rainfall outside of the higher terrain of the mountains. Because
of this, the concern falls into possible areal flooding, but
expected precipitation amounts are not high enough that widespread
flooding should be a concern. The NBM does produce a 40-100%
probability of 72-hour rainfall amounts 0.5 inch or more during
the start of the long term through Saturday, but increasing the
probability to an inch or more rapidly removes the majority of the
region outside of the mountains. Meanwhile, probabilistic
forecasts for area rivers to reach bankfull/action stage or higher
remain on the low side, around 10-20% through the duration of the
forecast period. Likely, expect some localized light ponding and
runoff to occur, but a heavy flooding event is not expected at
this time.

Of note at the end of the long term, a final cold front will move
across Sunday into Monday with post frontal northerly winds aloft
then expected, driving our temperatures back down to start next
week. While temperatures won't plummet significantly, it should
at least signal the return of sub-freezing overnight lows, with
high pressure finally making a return just beyond the end of the
period. Overall there is moderate to high confidence (60-70%) in
the long term, with confidence waning as the forecast period ends
due to ensemble differences in how the final system will depart
and high pressure will take over. Goatley/87

&&

.AVIATION...00Z TAFs...A mix of flight categories expected due to
expected overnight showers into tomorrow morning. For sites with
lower winds (DLS/YKM/PSC), can't rule out a chance at localized
lowered CIGs and possibly mist/fog outside of main bulk of
precipitation, but confidence is low. Other locations expected to
have periods of MVFR conditions possible with this rain, but
stronger winds should help prevent fog development. Wind gusts
20-30 knots expected all other sites. Low level wind shear
possible through 06Z for BDN/RDM, with some brief shear possible
near PDT between 03-06Z but expecting surface winds to rise after
this to alleviate it. Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  45  30  46 /  60  90  10  10
ALW  42  48  34  48 /  50  90  10  10
PSC  39  48  34  46 /  70  90   0  10
YKM  36  45  27  39 / 100  40   0  40
HRI  40  48  32  46 /  70  90   0  10
ELN  34  41  28  38 /  90  50   0  50
RDM  40  45  24  42 /  80  70   0  20
LGD  39  45  27  41 /  30 100  30  10
GCD  38  46  26  41 /  30  90  10  20
DLS  41  50  35  44 /  90  60  10  50

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 10 PM this evening to 7 AM PST Tuesday for
     ORZ049-508.

     High Wind Warning from 10 PM this evening to 7 AM PST Tuesday
     for ORZ507.

WA...Wind Advisory from 10 PM this evening to 7 AM PST Tuesday for
     WAZ029.

     Dense Fog Advisory until 5 PM PST this afternoon for WAZ026.

&&

SHORT TERM...74
LONG TERM....87
AVIATION...87