667
FXUS66 KPDT 141616
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
916 AM PDT Tue May 14 2024

.UPDATE...High pressure is well entrenched over the area this
morning. The disturbance that crossed the area yesterday has moved
into the Rockies and a northwest flow is in place overhead. It
should be a fair and sunny day with temperatures similar to
yesterday. This will be around 5 degrees above normal for mid May.
Did add partly cloudy skies this morning south of Bend due to
current clouds seen on satellite imagery though the clouds are
rapidly moving out of the area. Did adjust temperatures up a
degree or two in a few places. With the disturbance out of the
area, winds will be lighter in general, though wind gradients
between Seattle and the Tri-Cities remain elevated and anticipate
15 to 25 mph winds with gusts to 35 mph in the Kittitas Valley
through this afternoon before decreasing this evening.

The Naches River at Cliffdell continues to be running just below
bankfull this morning and is forecast to rise above bankfull later
today where it is expected to remain into next week. However, it
will remain well below minor flood stage. Probabilistic data gives
it a greater than 95 percent chance of reaching action stage in
the next 10 days but a less than 5 percent chance of reaching
minor flood stage. The Naches River at Naches is a bit more
complicated. The forecast keeps the Naches River at Naches below
bankfull through the next 10 days with a 9 percent chance of
reaching action stage. However, the current observations are
running about a third of a foot higher than the forecast. If we
shift the forecast up by a third of a foot, it still stays below
action stage, though just barely. Will be awaiting the new
forecast which should arrive in the next hour or two with
interest. Impacts should be minor if it does reach bankfull.
Perry/83

&&

.PREV DISCUSSION... /issued 221 AM PDT Tue May 14 2024/

SHORT TERM...Today through Thursday...Short term forecast will be
dominated by an upper level ridge positioned over the eastern
Pacific Ocean. This will keep the Pacific Northwest under a warm and
dry northwest flow pattern through Wednesday. High temperatures
today will be at or slightly above Monday`s highs followed by and
increase of around 5 degrees on Wednesday with highs in the 80s in
the lower elevations and 70s in the mountains. Winds will be
relatively light but there will be a weak marine push through the
gaps of the Cascades late this afternoon and evening producing some
locally breezy conditions along the east slopes of the
Cascades. This pattern repeats on Wednesday afternoon and evening.

On Thursday the high pressure over the eastern Pacific begins to
shift westward away from the coast which allows an upper level low
over Alaska to move into western Canada. This will push the jet
stream south over the Pacific Northwest and combine with an
increasing west to east pressure gradient to increase westerly winds
through the day and persist through the night.



LONG TERM...Friday through Tuesday...Guidance is in broad agreement
on a light to moderate NW flow pattern over the region, before
introducing the chance for broad troughing to envelop the forecast
area by the end of the period. Net effect will be generally
seasonable temps, periods of breezy conditions, and some occasional
chances for light orographic shower activity, primarily across the
central Washington Cascades.

Looking at model ensemble clustering, discrepancies really don`t
start to show up until around Monday next week. Until then, guidance
shows a cutoff low off the SoCal coast helping to initiate a NW flow
pattern over the PacNW. Deterministic guidance shows a more
amplified band of NW flow Friday, with those upper-level winds
looking to mix down to the surface during the day. NBM probabilistic
guidance already showing widespread likely (>70%) chances for gusts
to exceed 30 mph, however chances drop down considerably when
measuring for advisory-criteria winds. Despite the amplified flow
aloft, however, PoPs are low, as deterministic guidance shows PWATs
only in the 0.3 to 0.5 range, leaving only slight chances for the
high mountains, namely across the WA Cascades. This amplified
pattern persists through much of the weekend, however the wind
forecast trends downward as the NW flow aloft slackens a bit heading
into Sunday.

Monday onward is when ensembles start to produce diverging
solutions, mainly due to the timing of an oncoming broad trough
originating from the NNW. Adding to that, some cluster groups favor
a continuation of NW flow rather than the arrival of any kind of
trough. Across deterministic guidance, the GFS seems to favor the
troughing solution, while the ECMWF brings down a weaker trough
while keeping the persistent NW flow pattern in place. Should the
trough materialize, expect a drop in temps as it brings in colder
Canadian air, however precip chances will likely be limited, due to
how dry the oncoming airmass will be. We`re reaching the time of
year where, outside of idealized conditions, the boundary layer
across the forecast area is simply too dry to support widespread
precip under cooler, drier NW flow patterns.

Overall forecast confidence through the weekend is high (80%), while
Monday onward is moderate (50%). Only real sensible weather impact
expected through the long term will be periods of gusty conditions
under the NW flow pattern. Evans/74

AVIATION...12z TAFs...VFR conditions expected for the period. Skies
will be mostly clear outside of some light cirrus. Winds will be
breezy at times for DLS, but elsewhere, expect generally W/NW winds
less than 12 kts, becoming terrain-driven overnight. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  76  47  80  51 /   0   0   0   0
ALW  77  51  82  55 /   0   0   0   0
PSC  82  54  87  57 /   0   0   0   0
YKM  81  49  87  51 /   0   0   0   0
HRI  80  50  86  55 /   0   0   0   0
ELN  76  49  81  53 /   0   0   0   0
RDM  74  43  80  47 /   0   0   0   0
LGD  71  44  77  48 /   0   0   0   0
GCD  73  44  79  47 /   0   0   0   0
DLS  80  52  85  54 /   0   0   0   0

&&

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

$$

MORNING UPDATE...83
SHORT TERM...91
LONG TERM....74
AVIATION...74