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000
FXUS66 KPDT 240541 AAA
AFDPDT

Area Forecast Discussion...UPDATED AVIATION.
National Weather Service Pendleton OR
1041 PM PDT Tue Apr 23 2024

.SHORT TERM...Tonight through Thursday...The western USA is
currently under an upper lever ridge of high pressure that is slowly
moving eastward. This is in response to a split upper level trough
over the eastern Pacific Ocean moving towards the west coast. The
southern portion of the trough contains a closed low off the coast
of southern California providing some instability showers over the
Great Basin. The northern portion of the trough contains a closed
low just off the coast of central British Columbia. Both of these
system will move eastward over the next 24 hours and begin impacting
the forecast area in different ways. Some of the moisture over the
Great Basin will work its way into southern Oregon this evening
triggering some showers and possible thunderstorms with some showers
possibly clipping central Oregon. On Wednesday some of this moisture
could clip eastern Grant, Baker and Wallowa counties with a few
showers. Meanwhile, the northern low will move into Canada overnight
and Wednesday with the southern portion of the low sweeping a weak
cold front through the Pacific Northwest Wednesday. This will usher
some showers into the Washington Cascades but more impactful will be
the breezy to windy westerly winds that develop through the day and
continue overnight. Wind speeds are expected to remain below
advisory criteria in the range of 15-30 mph with gusts 30-40 mph.

The movement inland of this split trough Wednesday will allow a more
concentrated westerly flow pattern over the eastern Pacific. This
westerly flow will usher in a better organized weather system
directly into the Pacific Northwest on Thursday that will provide a
good chance of precipitation to the forecast area. This system does
not have much cold air associated with it as snow levels remain
around 5000 feet through Thursday night.

.LONG TERM...Friday through Tuesday...The long term will remain a
progressive pattern as multiple systems move across the region, but
aside from keeping temperatures on the mild to cooler side and
producing mostly mountain precipitation, significant concerns are
not anticipated during the period.

Friday begins with a trough dropping across the region that will
continue southeastwards through Saturday, becoming a cutoff low
across the Four Corners region. The inland PacNW remains under
troughing over the weekend, with a deep Alaskan low that will
descend down the Canadian coastline and approach the US before fully
moving over our area by the early to mid-week timeframe next week.

Overall sensible weather concerns from this progressive pattern are
expected to be fairly limited. Temperatures will remain near or
slightly below normal with highs in our population centers in the
upper 50`s to mid 60`s, with a few chances at low 70`s in the
Columbia Basin. Precipitation from the troughing pattern remains on
the low side, particularly in the lower elevations. Ensembles only
average a 10-40% probability of 0.1 inch QPF or higher for our lower
elevation zones for the 24 hour period of Friday morning through
Saturday morning (the best day for chances for precipitation).
Otherwise the mountains have a widespread 70-100% chance of the same
amount, with probabilities plummeting if we increase the amount to
0.5 inch outside of the highest elevations of the Cascades. The NBM
also expects a few thunderstorms with Friday`s precipitation across
the Ochoco-John Day Highlands through the Blues and Wallowas, but
probabilities are also on the low side (15-25%) as global models and
ensembles show very little favorable support for this activity (wind
shear, instability, etc). Expecting a few orographically driven
storms to be possible with primary impacts being lightning, brief
locally heavy rain, and some gusty non-severe outflow winds.

With Friday into early Saturday being the best chance of
precipitation, passing mountain showers and high
elevation/mountaintop snowfall will continue through the long term
period with the lower elevations having extremely low (15% chance of
less) to nil probabilities of showers under the progressive pattern.
But as the Alaskan low begins to approach on Sunday, ensembles are
indicating the potential for some breezy winds Sunday evening into
early Monday. Ensemble probabilities for gusts greater than 20 knots
are high across Washington and Northern Oregon (60-100%), but
probabilities for gusts of 34+ knots fall nearly completely off,
meaning we`ll likely see some breeziness as the pressure gradients
tighten, but more significant activity that could lead to at least
advisories is doubtful. Overall the pattern remains active enough,
but not enough to bring noteworthy concerns to the forefront at this
time. Goatley/87


&&

.AVIATION...06Z TAFs...VFR conditions area-wide with VFR
conditions expected to persist through the TAF period. Limited
concerns the next 24-hrs. The latest satellite imagery shows high
clouds have pushed off east with mainly clear skies overhead, except
mid-high clouds across the central OR mountains and far eastern
mountains. The next disturbance is apparent in satellite imagery
upstream in the eastern North Pacific offshore the WA/OR coast that
will move across the area tomorrow in tandem with a weak cold front
passing through in the afternoon. This will promote breezy winds
with modest gusts. High confidence (>90%) in gusts 22 kts/25 mph or
more across the KDLS and KPDT terminals, less confident in these
gusts across KALW and KPSC (50-80%). Decent potential for peak daily
gusts 30 kts or more at KPDT and KDLS as well (60-70%), albeit would
not be expected to be frequent. Elsewhere, winds not as strong at
other TAF terminals with gusts generally 15-20 kts. Thereafter
elevated winds will prevail tomorrow night.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  67  43  62 /   0   0   0  20
ALW  40  70  47  66 /   0   0   0  20
PSC  41  72  48  69 /   0   0   0  10
YKM  40  70  43  64 /   0   0   0  20
HRI  38  72  46  67 /   0   0   0  10
ELN  39  62  43  61 /   0   0   0  20
RDM  33  65  37  57 /   0   0   0  30
LGD  39  67  40  61 /   0  10   0  20
GCD  39  70  40  61 /   0  10   0  30
DLS  42  69  48  60 /   0   0   0  40

&&

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

$$

SHORT TERM...91
LONG TERM....87
AVIATION...80