067
FXUS66 KPDT 262138
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
238 PM PDT Thu Sep 26 2024

.SHORT TERM...This afternoon through Saturday night...Aside from
likely (55-90% chance) rain showers along the Washington Cascade
crest late this evening through tonight as a Pacific frontal
system (warm front with trailing cold front) moves onshore and
weakens, dry weather is forecast through the period. The frontal
system will usher in locally breezy southwest to west winds along
exposed ridges of the Simcoe Highlands and east slopes of the
Washington Cascades overnight, but the probability of advisory-
level gusts is low (30-40% chance).

NWP guidance is then in excellent agreement in a dry, quasi-zonal
mid-level flow for Friday, with the only noteworthy talking point
being a warming trend and locally low afternoon RH. Saturday, the
warming trend continues, especially across the Blue Mountains
region as rising heights and southwesterly flow facilitate an
unseasonably warm air mass (ECMWF EFI of 0.5-0.8 for maximum
temperature). Low afternoon RH is also anticipated across the
aforementioned area Saturday afternoon, but confidence in
sustaining wind and RH Red Flag criteria is low (<30%).

Late Saturday afternoon through Saturday night, westerly gap flow
will increase in magnitude as cross-Cascade surface pressure
gradients tighten in response to a mid-level shortwave trough
passing across far northern Washington. Chances of precipitation
are very low (5-14%) along the Washington Cascade crest.
Plunkett/86

&&

.LONG TERM...Sunday through Thursday...An overall quiet pattern is
expected through the extended period.

On Sunday, the flow will be mainly westerly, but a very weak trough
will move across the region. This feature will do nothing more
than bring some low precip chances to the higher elevations of the
Washington Cascades. Behind this trough, a dry northwesterly flow
moves over the area with some ridging building in from the south.

The next chance of precipitation arrives on Tuesday, again for the
Washington Cascades, when a cold front and trough move across the
area. The model guidance is in excellent agreement through
Wednesday, but then begin to vary with respect to the timing and
strength of the trough, with the ECMWF being a bit stronger and
deeper with the trough. The GFS ensemble mean is in better
agreement with its deterministic run at 500 mb than the ECMWF
during the Wednesday time period, giving some more credence to its
solution.

There will be diurnal breezy winds Sunday, especially across the
Simcoe Highlands, Columbia Basin and Kittitas Valley with winds
around 30 mph, and possibly higher. NBM probabilities of wind
gusts >= 39 mph generally range from 50 to 80 percent with the
highest values in the Kittitas Valley. The ECMWF EFI also keys in
on the winds and wind gusts during the Sunday time frame with
values ranging from 0.5 to 0.7 mainly across the Columbia Basin
and adjacent valleys.

There will be diurnal breezes Tuesday and Wednesday as well with
gusts generally around 20 mph, though there is considerable
uncertainty on Wednesday depending on the cold front and trough,
winds could end up being higher.

&&

.AVIATION...18Z TAFS...VFR conditions with winds less than 10 kts
are expected through the TAF period.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  77  47  77 /   0   0   0   0
ALW  53  80  51  81 /   0   0   0   0
PSC  55  80  50  80 /   0   0   0   0
YKM  46  77  44  78 /   0   0   0   0
HRI  51  80  49  80 /   0   0   0   0
ELN  49  74  44  78 /  10   0   0   0
RDM  43  78  43  83 /   0   0   0   0
LGD  48  80  48  88 /   0   0   0   0
GCD  48  82  50  90 /   0   0   0   0
DLS  54  79  51  81 /  10   0   0   0

&&

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

$$

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