557
FXUS66 KPDT 190926
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
226 AM PDT Thu Sep 19 2024

.SHORT TERM...Today through Saturday...A cutoff low centered over
California continues to beget weak NW flow into our forecast area,
making for dry conditions through the period. Only real sensible
weather concern for the next couple of days will be an uptick in gap
flows across primarily the Columbia River Gorge and the Kittitas
Valley, where NBM probabilistic guidance depicts a 50-70% chance of
gusts exceeding 40 mph both Thursday and Friday. This is due to a
weak shortwave allowing for stronger NW winds aloft through the
forecast area. Models, however, do not show winds extending very far
beyond the Cascade Gaps, giving credence to the idea that these
winds are primarily driven from aloft rather than via pressure
gradient.

There is a slight chance (15%) for the central Washington Cascades
to see a weak orographic shower during the period, but any impacts
are expected to be minimal. Otherwise, expect a clear and
(relatively) warm day today, before temps trend more toward seasonal
averages Friday and Saturday as the aforementioned shortwave allows
for a (relatively) cooler airmass to advect into the Interior
Northwest. May need to keep an eye out for overnight lows Saturday
morning across our elevated valleys such as central Oregon and
Wallowa County, as guidance does suggest overnight lows may
flirt with freezing there. Evans/74

.LONG TERM...Sunday through Thursday...Ensemble runs remain in
good agreement through the period but GFS and ECMWF deterministic
runs are showing dramatic differences developing by days 6
and 7.

Sunday will begin under a dry westerly flow but then switch to
northwest flow behind the passage of a weak upper level trough
through western Canada. This will be a dry trough passage other than
a low chance of showers in the Washington Cascades. Main impact will
be some locally breezy winds. A ridge of high pressure over the
eastern Pacific Ocean with then push into the Pacific Northwest
Monday and Tuesday lifting high temperatures to 5-10 degrees
above normal.

Wednesday and Thursday according to the ensemble runs should see the
upper level ridge moving off to the east while an upper level trough
from the Gulf of Alaska slowly pushes towards western Canada the
Pacific Northwest. However, deterministic runs show the ECMWF
holding the upper level ridge in place over the region longer with a
slower progression of the Gulf of ALaska trough towards the Pacific
Northwest. Meanwhile, the GFS sweeps the trough through the region
rapidly Wednesday with a chance of precipitation followed by a
westerly flow Thursday. The forecast reflects the ensemble version
of events with some increasing low chance pops mainly along the
Washington Cascades but there is a high degree of uncertainty based
on the deterministic differences.

&&

.AVIATION...12Z TAFs...VFR conditions expected over the next 24
hours under generally clear skies. Winds will be light through the
morning then see increasing west to northwest winds 5-15kts through
the afternoon and evening. DLS will see stronger winds at 10-20kts
and gusts around 30kts.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  77  47  69  41 /   0   0   0   0
ALW  79  51  71  44 /   0   0   0   0
PSC  81  53  75  46 /   0   0   0   0
YKM  81  47  75  41 /   0   0   0   0
HRI  81  52  75  44 /   0   0   0   0
ELN  76  50  71  43 /   0   0   0   0
RDM  77  42  71  36 /   0   0   0   0
LGD  78  45  68  40 /   0   0   0   0
GCD  78  44  72  37 /   0   0   0   0
DLS  79  53  73  48 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...74
LONG TERM....91
AVIATION...91