306
FXUS66 KPDT 082358 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
500 PM PDT Sat Jun 8 2024

Updated Aviation Discussion



.SHORT TERM...Today through Monday...

Bottom Line Up Front (BLUF)

1. Thunderstorms over south central OR and along the eastern
mountains today and Sunday afternoon.

2. Warmer than average temperatures today before leveling towards
normal.

3. Winds increase again Sunday.

Hi-res models are in decent agreement with the upper level synoptic
pattern through tonight. An upper level ridge has shifted east of
the region as the leading edge of an upper level trough makes its
way onshore. Mid level moisture will enhance as the southwesterly
flow intensifies ahead of the the upper level trough. This synoptic
set up will lead to thunderstorm probabilities across southern
Deschutes, Crook and Grant Counties. The SPC has a marginal
thunderstorm outlook over the southern portion of the CWA today then
it switches to a general thunderstorm outlook along the eastern
mountains on Sunday. Model derived soundings across the the
aforementioned counties show MUCAPE values of 200-400 J/kg, lapse
rates over 8.5 C/km, lifted index of -2 to -3, PWATs of 0.77 inches
and bulk shear near 25 kts. As the upper level trough continues to
push onshore, thunderstorm ingredients are projected to continue
through Sunday and move along the Ochoco-John Day Highlands and
across the eastern mountains into Wallowa County. Model derived
soundings again show MUCAPE of 400-600 J/kg, lapse rates of 7.6
C/km, lifted index of -3 to -4, PWATs of 0.90 inches and bulk shear
nearing 30-40kts. The strongest of the ranges being in Union and
Wallowa Counties Confidence in these storms becoming severe is low
from the SPC guidance, less than 5%.

Even with the incoming frontal boundary and upper level trough,
temperatures are going to remain slightly above to near normal.
Models show the upper level trough to be mostly dry and `cooler`,
only dropping the temperatures as few degrees Sunday. EFI is
signaling above average temperatures for much of OR today  and
leveling back to near normal on Sunday through Monday. Over 80% of
the raw ensembles show that today, much of the region will be in the
upper 80s with some isolated 90s in the Basins, mid elevations like
central and north central OR will be in the mid to upper 80s and the
higher terrains will be in the high 60s to low 70s. Models then show
the trough axis to be onshore Sunday which will push a frontal
boundary across the Cascades allowing some `cooler` air to rush into
the area. Temperatures will only cool by a few degrees with over 80%
of the raw ensembles showing temperatures in the mid to upper 80s
through the Basins, upper 70s to low 80s along the lower and mid
elevations and low 60s along the higher elevation. Over 80% of the
raw ensembles show Monday to be much the same as Sunday. There is an
enhanced heat risk today for portions of the Basin where HeatRisk
guidance is signaling moderate risk, so be mindful if outside and
remember to drink plenty of fluids.

Lastly, with the upper level trough pushing across the Cascades,
model derived pressure gradient tool shows that there is a slight
tightening of the surface gradients along the Cascades of 9 to 11
mb. While this is not wildly different from what is considered
normal, it is elevated. Due to this, ensembles are picking up on
increased winds, especially through our wind prone areas. There is
over a 55-75% chance the Simcoe Highlands and portions of the Gorge
seeing winds of 25 mph or greater, 70-80% through the lower Kittitas
Valley and a 65-70% along the foothills of the Blues. Bennese/90



.LONG TERM...Tuesday through Saturday...Westerly zonal flow on
Tuesday will bring a low (20%) chance of some showers to the
Washington Cascades into Tuesday night, while the rest of the are
will be dry.  A cold front will cross the region on Tuesday.

Dry weather will continue into early Friday before southwesterly
flow returns and so do precipitation chance, mainly to the Cascades
through Saturday, again with most of the rest of the region
remaining dry.

There is considerable uncertainty as we head toward next weekend
regarding the evolution of the pattern, with a trough expected to
move onshore in the Pacific Northwest.  The deterministic ECMWF is
weaker and considerably faster with the trough than the GFS.

As we approach the weekend, the ensemble clusters are a bit more
supportive of the ECMWF solution (37%) by Friday, though at that
time range there is general uncertainty anyway.  There is definitely
going to be a trough, it is more of a question of exactly when.  By
Saturday, the ECWMF has 36% of the clusters while the GFS has 32%,
so not much difference.

It will be breezy on Tuesday with the passage of the cold Front in
the Columbia Gorge, Basin, Simcoe Highlands, Kittitas Valley. Wind
gusts in the 25 to 35 mph range are anticipated.

It will also be breezy around Friday (or whatever day this occurs)
as the trough moves onshore, especially in the Basin, Gorge,
Kittitas Valley.

High temperatures will go from about 10 degrees above normal on
Tuesday from the mid 80s to near 90 degrees in the Columbia Basin to
about 5 degrees above normal on Wednesday with highs from the upper
70s to mid 80s.  Thursda`s highs will be similar to Tuesday, as
highs increase in southwesterly flow.  By Friday, and especially
Saturday, highs will be close to, or even slightly below normal due
to the trough, though there is uncertainty.  Highs will range from
the upper 60s to upper 70s.


&&

.AVIATION...00Z TAFS...BKN-OVC mid and high level clouds will
remain through Sunday afternoon.  Winds will also be 15 kt or less
with strongest winds at KDLS, KRDM and KBDN before sunset.
Thunderstorms have developed in south central Oregon...a little
farther south than most of the CAMS advertised.  The embedded wave
triggering the isolated activity will travel to the northeast and
bring showers and thunderstorms, but mainly over the eastern
mountains and valleys. I included VCSH in the TAF for RDM and BDN
for the early morning hours based on model QPF over central OR, but
the VCSH may be removed based on the track of the weak wave.
Wister/85



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  80  56  83 /   0  20  10   0
ALW  61  83  59  85 /   0  20  10   0
PSC  62  87  60  89 /   0  10  10   0
YKM  59  86  53  87 /  10  30  10   0
HRI  62  87  59  88 /   0  20  10   0
ELN  61  82  55  81 /  10  30  10   0
RDM  56  80  47  82 /  20  30   0   0
LGD  57  76  51  79 /  20  40  10   0
GCD  56  78  49  82 /  30  40  10   0
DLS  64  83  56  84 /  10  10   0   0

&&

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

$$

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