000
FXUS66 KPDT 052113
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
213 PM PDT Wed Oct 5 2022

.SHORT TERM...Wednesday through Friday...High pressure remains in
place as the region finds itself in a bit of a blocking pattern,
saddled between a deep low over the central Pacific and a cutoff low
over the desert SW. Overall forecast trend remains the same as a
result, with clear skies, light winds, and unseasonably warm
temperatures. Stagnant conditions may also make for some hazy skies
as regional wildfires persist, but a quick look at webcams around
the forecast area suggests any visibility impacts look to be
limited. AQI had started to edge toward the moderate threshold
across much of the Basin as a result of the stagnant conditions,
which may persist into early next week so long as ridging remains in
place. Elevated smoke and haze may also inhibit daytime heating as
well.

Overall looking at a persistence forecast, with highs in the low to
mid 80s across our population centers, inching closer to the upper
80s in the Gorge. A deepening of the offshore low on Friday may work
to retrograde the ridge axis and thus cool temperatures a tad, but
conditions still look to remain quiet throughout the period.
Evans/74

.LONG TERM...Saturday through Wednesday...The upper ridge will
retrograde westward with the ridge axis becoming established off
the west coast. This will put the forecast area in a northwest
flow on the east side of the ridge on Saturday. Despite the
northwest flow, temperatures are expected to remain warmer than
normal through Sunday. However, the NBM 1D viewer temperature
forecasts have a great amount of variance with differences as much
as 15 degrees between the 25th and 75th percentile. Maximum
temperature forecasts by the NBM are in the lower to mid 80s
across the lower elevations on Saturday and Sunday. Due to the
amount of uncertainty, will lean with the NBM temperature
forecasts. 850 mb temperatures by the GFS deterministic model are
forecast to be in the mid to upper teens degrees C during the
afternoons. That equates to surface temperatures in the lower to
mid 80s under mostly clear skies and maximum solar radiation. The
mountains will have maximum temperatures in the mid 60s to mid
70s, with some mountain valley locations, such as the Grande Ronde
Valley, in the upper 70s to near 80. Conditions during this
period will be dry and stable with mostly clear skies, with maybe
just some high thin clouds.

On Monday, a strong cold front and a deep upper trough/upper low
over western Canada will move south to southeast and bring much
cooler temperatures to the region. There will be upslope showers
with the cold front by Monday afternoon over the eastern/northeast
mountains, as well as the Cascade east slopes of both OR and WA.
However, precipitation amounts will be very light. Storm total QPF
amounts are forecast to be the greatest in the northern Blue
Mountains with several tenths of an inch. Other areas are expected
to receive zero to less than a tenth of an inch, except for the
Wallowas and Elkhorn Mountains, which may receive one to two
tenths of an inch. Snow levels are forecast to lower to 4500-5500
ft MSL by Tuesday morning. This may result in light amounts of
snow over the higher peaks and ridges, with perhaps a dusting to
an inch of accumulation. The lower elevations are expected to
remain dry with this system. Low temperatures are forecast to be
in the mid 30s to lower 40s in the lower elevations by Wednesday
morning. There will likely be areas of frost, possibly even in the
lower elevations, in sheltered locations, Tuesday night and
Wednesday night. Maximum temperatures are expected to be in the
70s in the lower elevations and 60s in the mountains on Monday,
and then only in the lower to mid 60s lower elevations and mid 40s
to mid 50s in the mountains on Tuesday.

Ensemble cluster analysis for days 6 and 7 (Tuesday and
Wednesday) shows significant amounts of variance, with some
clusters having the upper low/trough further west over the
forecast area, while other clusters have the upper low/trough
further east, with a northwest flow over the forecast area. There
are also significant differences between the deterministic
models. The GFS brings a deep closed upper low over the forecast
area, further west, while the ECMWF brings a less amplified upper
trough, that is further east, over the PacNW on Tuesday and
Tuesday night. Therefore, at this time, there is low confidence in
the forecast position and depth of the upper trough/low for
Tuesday and Wednesday due to these significant differences. For
now, will go with the NBM solutions until the ensembles and
deterministic models come into better agreement.

It will become breezy to windy, especially in the lower
elevations, by Monday afternoon, due to much increased pressure
gradients. The elevated wind speeds will continue into Tuesday,
especially during the afternoons and evenings. At this time, wind
speeds are not expected to reach advisory criteria. However, due
to the uncertainty in the deterministic models and the ensembles,
the forecast wind speeds could change and become either stronger,
perhaps to advisory criteria, or they could become weaker. Will
need to keep a close watch on this as time progresses and as
conditions evolve. 88

&&

.AVIATION...18Z TAFs (Previous Discussion)...VFR conditions will
persist through the 24 hour forecast period. There will be high
thin cirrus at or above 250. Winds will be light and under 10 Kts
at all terminals. 88

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  80  49  79 /   0   0   0   0
ALW  50  81  51  79 /   0   0   0   0
PSC  51  83  52  81 /   0   0   0   0
YKM  48  83  50  82 /   0   0   0   0
HRI  50  83  51  81 /   0   0   0   0
ELN  48  83  49  82 /   0   0   0   0
RDM  42  81  45  80 /   0   0   0   0
LGD  47  81  46  80 /   0   0   0   0
GCD  46  85  48  84 /   0   0   0   0
DLS  55  87  55  87 /   0   0   0   0

&&

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

$$

SHORT TERM...74
LONG TERM....88
AVIATION...88

NWS PDT Office Area Forecast Discussion