936
FXUS66 KPDT 090536
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1040 PM PDT Sat Jun 8 2024

Updated Aviation Discussion

.SHORT TERM UPDATE...Strong to severe storms developed over Lake and
Harney Counties this evening, and there have been some CG lightning
associated with these large cells in far southern Crook and Grant
Counties. We will continue to monitor these storms as they track
to the northeast, but it looks like the stronger storms will skirt
past our forecast area this evening with the exception of Grant
County east of Seneca. The confidence is around 70% due the latest
00Z HREF composite reflectivity progs. The steering flow is very
weak, and storms have only been moving around 8-15 mph based on
KCBX storm motion and H7 winds around 10 kt. Foster Flat RAWS site
in Harney County measured 0.64", so the slow moving storms will also
bring heavy rain.  Eyes will be focused on the radar and
observations through the night.

After midnight, the southwest flow aloft will increase ahead of an
approaching shortwave trough.  Showers and thunderstorms will
increase over eastern Oregon, mainly Grant, Union and Wallowa
Counties early Sunday morning. MUCAPES from CAMS go as high as 500
J/kg and mainly over southeast Oregon.  There is elevated
instability with negative theta-e lapse rates and DIV Q aloft. The
chance of showers is around 30-50% for Sunday morning and the chance
for thunderstorms is around 20-30%.

Forecast was updated to reflect the current conditions and change
the "chance" wording to "scattered" over our southeast zones.
Otherwise, no updates needed.  Wister/85


&&

.AVIATION...06Z TAFs...Storms have stayed away from the vicinity of
the terminal airports, and any threat of storms through Sunday
morning is minimal (0-20% with highest probability in KPDT).
However, there will be showers over the northern Blues Sunday
morning and in the vicinity of PDT.  Through 22Z Sunday, mid and
high level clouds will vary with bases 8-15 kft.  After 22Z, clouds
will decrease to FEW-SCT altocumulus. Winds will be 15 kt or less
with the exception of DLS where NW winds will increase to around
17G27kt Sunday afternoon.  NW winds gusting to 22 kt are forecast
for RDM in the afternoon.  Wister/85

&&



.PREV DISCUSSION... /issued 500 PM PDT Sat Jun 8 2024/

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. 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.


&&

.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...90/85
LONG TERM....77
AVIATION...85