611
FXUS66 KPDT 192342
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
442 PM PDT Thu Sep 19 2024

.AVIATION...00Z TAFs...VFR conditions forecast for all sites
through the TAF period. Southerly drainage winds overnight in
central Oregon may push smoke/haze from area wildfires across
BDN/RDM, but confidence in sub-6SM VSBYs and/or an opaque smoke
layer is low (<30%). Otherwise, expecting cloud cover to consist
of FEW-SCT250 for TAF sites. Sustained winds of 12 kts or less
with higher afternoon/evening gusts, except for DLS. Plunkett/86

&&

.PREV DISCUSSION... /issued 201 PM PDT Thu Sep 19 2024/

SHORT TERM...Tonight through Saturday night...Overall, a quiet
period of weather is in store. Low pressure off of the central
California coast will gradually move south and eastward through
Friday. The trough associated with this low will keep northwest
flow over the Pacific Northwest.

As the low moves further inland, some ridging will build in for
Saturday, with a weak trough approaching Saturday night. There
could be a passing shower over the higher terrain of the Cascades
later tonight or toward Friday morning, but probabilities are low
(<20%). Any showers received there are the only precipitation
chances across the area through Saturday night.

Breezy winds have been occurring today in the normally affected
spots...the Kittitas Valley, Simcoe Highlands, portions of the
Columbia Basin, with gusts generally to around 30 mph. These gusts
are expected again on Friday in the northwest flow, though
guidance suggests they will be possibly less. NBM probabilities of
gusts >=39 mph are 50 to 70 percent in the Kittitas Valley and
much less elsewhere...generally 30 to 40 percent with some
isolated 50 percent values in the Columbia Basin and Simcoe
Highlands.

Low temperatures Saturday morning will be chilly in some of the
higher elevations and elevated valleys. Right now, temperatures
will be just above to right around freezing but will have to see
what future guidance does and where to determine if any freeze
warnings are necessary.

LONG TERM...Sunday through Thursday...

Bottom Line Up Front

1. WA Cascade rain, dry conditions elsewhere

2. Breezy Cascade Gaps

3. At or near normal temperatures

Models show the beginning of the period to be under dry westerly
flow as the upper level low continues to traverse to the south and
another begins to push in from the northwest. As the trough to the
northeast Sunday, upper level flow will turn slightly northwest
and bring in light precipitation to the WA Cascades. Not only will
this shift bring light rain, winds will also increase slightly
through the wind prone areas of the Cascade Gaps as well as allow
for temperatures to remain at or near normal through the period.
However, models do become a bit chaotic around days 6 and 7 and
are out of sync as to whether we will be under a tough or a ridge.


Models show an upper level trough beginning to slide down the
Canadian coast and towards the PacNW with a ridge trying to
undercut it. Regardless, the leading edge of the system will
bring some precipitation to the crests of the WA Cascades. 20-40%
of the raw ensembles show only 0.3-0.5 inches of rain likely as
the system crosses over the Cascades. Once the system passes over,
dry conditions across the entire CWA are expected as the ridge
undercuts the trough and moves over the area.

With the leading edge of the system pushing across the region,
surface pressure gradients tighten ever so slightly allowing for
slightly breezy conditions through the Cascade Gaps. However, only
20-30% raw ensembles are showing sustained winds of 20 mph or
greater. As the flow shifts to southwest flow under the ridge,
diurnal winds through the Gaps will return with typical breezy
conditions of less than 10 mph will return.

Lastly, EFI shows temperatures to continue to be at or near normal
through the forecast period. NBM shows at the beginning of the
period to be in the mid to upper 70s across much of the lower
elevations with so isolated 80s in the Basin and Gorge. As the
upper level ridge moves overhead, NBM shows temperatures to begin
to hedge more towards the upper 70s to low 80s with the Columbia
Basin seeing mid 80s and 70-80% of the raw ensembles are in
agreement. Looks like we will see a brief warm up again next week.
Enjoy it while it lasts. Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  69  41  70 /   0   0   0   0
ALW  51  72  45  73 /   0   0   0   0
PSC  52  75  46  74 /   0   0   0   0
YKM  44  75  41  75 /   0   0   0   0
HRI  51  74  44  74 /   0   0   0   0
ELN  49  72  43  77 /   0   0   0   0
RDM  40  72  36  72 /   0   0   0   0
LGD  43  69  40  71 /   0   0   0   0
GCD  42  71  38  72 /   0   0   0   0
DLS  52  72  48  79 /   0   0   0   0

&&

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

$$

SHORT TERM...77
LONG TERM....90
AVIATION...86