Pendleton, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

329
FXUS66 KPDT 301117
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
317 AM PST Thu Jan 30 2025

.SHORT TERM...Today through Saturday...Today will mark the last day
of what`s been an extended period of cold and dry conditions. A warm
front will lift through from the southwest and provide the forecast
area with a shot of moisture Thursday night into Saturday, with
heavy mountain snow and lowland rain expected. This will be followed
by an atmospheric river overlying the forecast area over the
weekend, but due to its zonal orientation, the biggest impacts from
this river are expected to remain in the mountains.

Winter Storm Watches remain in effect for our Cascade zones, with
the addition this morning of the northern Blues above 4000 feet as
both Friday`s snow and Saturday`s atmospheric river look to provide
the Tollgate/Ski Bluewood area with warning-criteria snow above a
foot. Thinking that the I-84 mountain pass through the Blues will
only see a couple of inches. Precip is expected to begin late
tonight in the Cascades, before enveloping the forecast area by
daybreak Friday. There was concern of icy precip in the previous
forecast during the onset of precipitation due to the timing of an
early morning arrival combined with recent cold pooling,
particularly for parts of the WA Columbia Basin and adjacent
valleys. While a brief spurt of light freezing rain cannot be ruled
out, current thinking is that cold pooling isn`t quite as robust as
what we`d like to see for a better freezing rain threat (highs in
the area have approached the 40s recently), plus CAMs are not really
depicting much ice across most recent runs. Oncoming cloud cover
ahead of the warm front will also help prevent temps in the Basin
from bottoming out too much. Left a 20% chance of -fzra occurring
around the Hanford area, based on model soundings and NBM
probabilistic guidance, but as of now am expecting primarily rain in
the forecast.

Snow may transition to rain Friday afternoon across the high
mountains as warmer air surges in behind the front, but snow levels
are expected to come back down again as cold air moves in associated
with a broad trough centered over western Canada, the main system
driving the weekend`s atmospheric river. Models seem to be trending
towards bringing the axis of moisture transport southward more
towards southern Oregon over the weekend, which would allow colder
air to intrude further south and provide more snow to areas such as
the John Day/Ochoco Highlands, while leaving the lowlands heavily
rain shadowed. The best threat for area-wide precip still looks to
be during the day Friday, although with amplified zonal flow
overhead in the form of the aforementioned atmospheric river, expect
the high mountains to be pounded with precip over the coming days,
hence why the Winter Storm Watches go out until Saturday afternoon.

Only other concern to mention is the presence of gusty winds, both
with the arrival of the warm front Friday and with amplified flow
overhead Saturday. Chief area of concern for headline-criteria winds
would be the foothills of the southern Blues on Friday, as to be
expected with a warm front passage, but confidence wasn`t quite high
enough to pull the trigger on an advisory. Still, expect winds in
this area to approach 40 mph at times Friday afternoon and evening,
with widespread 25-35 mph gusts across the rest of the forecast
area, with the threat persisting into Saturday, especially for areas
downwind of the Cascades. Evans/74

.LONG TERM...Sunday through Wednesday...The extended period looks
to be quite unsettled.

Westerly flow will prevail at the beginning of the extended period,
as a low develops off of British Columbia.  This low will move
southwest and carve out a trough through midweek.  As this occurs,
moisture in the southwest flow ahead of the low, in the form of an
atmospheric river will begin to move onshore on the Pacific coast.
The low itself and upper trough is expected to approach the coast
toward the end of the extended period.

Overall, the upper air pattern between the deterministic GFS and
ECMWF is fairly similar, though the GFS is slightly deeper with the
low off the British Columbia coast.  All of the guidance, the GFS,
ECMWF and CMC have trended south with the location of the
atmospheric river.  The CMC and GFS now center it over northern
California, while the ECMWF is further north over California and
Oregon.  However, due to the more southern position, QPF values, and
with the lower QPF, comes lower snow amounts as well.  Ultimately it
will depend on which model is most correct or if the southerly trend
continues.  While there could still be mountain snow, especially if
the ECMWF solution is correct with the latest trends the potential
for lowland snow is much reduced.

The 24 hour probability of >=4 inches of snow is >90 percent for
Snoqualmie Pass and the higher elevations of the Washington Cascades
or the period ending Sunday morning.  Percentages are also 80 to
100% for the crest of the Oregon Cascades.  However, for the crest
of the Blue Mountains, percentages are only about 50 to 60% at this
time.

The 24 hour probability of >=4 inches of snow ending Monday morning
decreases to about 80 to 90% at Snoqualmie Pass and the crest of the
Washington Cascades, about 60 to 80% along the crest of the Oregon
Cascades and about 30 to 40% along the crest of the Blue Mountains.

For the lower elevations (Columbia Basin, Blue Mountain Foothills,
Yakima Valley), there is about a 10 to 20% probability of around an
inch Tuesday morning.

By Wednesday, with the low and trough pushing closer, even the
wetter ECMWF solution has the moisture from the atmospheric river
pushed eastward though there will be lingering moisture from the low
and trough itself.

There will be some mainly diurnal breezes Sunday into Monday and
then again Tuesday with speeds generally up to around 20 mph.

Temperatures will be near normal Sunday, then about 10 to 15 degrees
below normal for the balance of the period, as highs remain in the
30s.

&&

.AVIATION...12Z TAFS...VFR conditions are expected through the
TAF period at most TAF sites. The only exceptions are at PSC,
there could be some MVFR CIGS/VSBYS early this morning. Also at
DLS, there could be some MVFR VSBYS in -RA Friday morning. A
weather system will bring precipitation to the region from west to
east beginning early Friday morning with DLS, BDN and RDM seeing
-RA before the end of the TAF period. It is possible YKM see some
precipitation as well but confidence is too low (<30%) to include
in the TAF at this time. The other sites will see -RA after the
end of the current TAF period. Winds are expected to be very light
through the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  33  50  34 /   0  20  90  70
ALW  45  34  49  35 /   0  20  90  80
PSC  42  33  48  36 /   0  30  80  50
YKM  41  30  43  27 /   0  40  90  60
HRI  44  34  49  35 /   0  30  90  50
ELN  39  30  40  25 /   0  30  90  60
RDM  57  35  48  28 /   0  20  90  80
LGD  45  32  39  33 /   0  20 100  90
GCD  52  33  45  35 /   0  20 100  70
DLS  48  37  48  34 /   0  70 100  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 AM PST Friday for ORZ041-044-507-
     508-510-511.

     Winter Storm Watch from late tonight through Saturday afternoon
     for ORZ502.

     Winter Storm Watch from this evening through Saturday afternoon
     for ORZ509.

WA...Air Stagnation Advisory until 4 AM PST Friday for WAZ024-026>029-
     521.

     Winter Storm Watch from late tonight through Saturday afternoon
     for WAZ030.

     Winter Storm Watch from this evening through Saturday afternoon
     for WAZ522.

&&

$$

SHORT TERM...74
LONG TERM....77
AVIATION...77