399
FXUS66 KPDT 092318
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
417 PM PDT Sun Jun 9 2024

Updated aviation discussion

.SHORT TERM...Today through Tuesday...

Bottom Line Up Front (BLUF)

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

2. Sub advisory winds Tuesday.

3. Near normal to normal temperatures return.

Current radar is showing a few cells moving across the area putting
down some rain. The line of precipitation has shifted eastward with
the frontal boundary. Ground observations show that 0.03 inches of
rain has fallen over the Ochoco-John Day Highlands and has continued
to move northeastward. We had a nice cell move over Pendleton a bit
ago and dumped roughly 0.03 inches of rain so far. These showers
will continue off and on through the evening.

Hi-res models are in good 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 general
thunderstorm outlook across the CWA. As the upper level trough
continues to push onshore, thunderstorm ingredients will continue
through this evening and move along the Ochoco-John Day Highlands
and across the eastern mountains into Wallowa County. There is also
a slight chance (<25%) of thunderstorms along the Cascades and
portions of far northern Kittitas County. Model derived soundings for
the Cascades with MUCAPEs of 300-600 J/kg, lifted index of -3 to -4,
however, the lapse rates are low at 7.4 J.kg and bulk shear is week
at 20 kts. Confidence in thunderstorms occurring over the
aforementioned area is low (10%). Looking at the eastern mountains
however, model derived soundings continue to show MUCAPE of 400-600
J/kg, lapse rates of 8.4 C/km, lifted index of -3 to -4, PWATs of
0.78 inches and bulk shear nearing 40kts. The strongest of the
ranges being in Union and Wallowa Counties. Confidence in
thunderstorms continuing to occur over the eastern mountains is
moderate (30-50%).

The upper level trough pushing across the Cascades, model derived
pressure gradient tool shows that there is a tightening of the
surface gradients along the Cascades of 9 to 11 mb as another
shortwave ripples across the region causing a surface pressure
gradient across the Cascades. Due to this, ensembles are picking up
on increased winds, especially through our wind prone areas. There
is over a 60-75% chance the Simcoe Highlands and portions of the
Gorge seeing gusts of 45 mph or greater, 70% through the lower
Kittitas Valley and a 65% along the foothills of the Blues. Will
continue to monitor the winds as the system draws near.

Lastly, temperatures will slowly moderate back to near normal
through Tuesday. However, EFI is picking up on above average
temperatures along the eastern mountains on Tuesday. Regardless,
temperatures will moderate a few degrees through the period. Over
55% of the ensembles have temperatures above 75 degrees today with a
few isolated location in the Basins seeing low 80s while the higher
terrains will see temperatures in the upper 60s to low 70s.
Temperatures will remain much the same daily through the period.
Bennese/90

.LONG TERM...Wednesday through Sunday...Dry westerly flow will
prevail over the Pacific Northwest through early Friday. Then the
flow will become more southwesterly in response to an approaching
trough.

As the trough approaches, there will be some rain over the
Washington Cascades on Friday, with other locations remaining dry.
The rain will progress to the Oregon Cascades on Saturday and into
the eastern mountains by Sunday.  However, most of the rest of the
area will remain dry.

There still is considerable uncertainty as to the exact strength and
position of the upper trough with the latest ECMWF deterministic run
keeping the trough over southwestern Canada while the GFS brings the
trough further south across the Pacific Northwest.  The ensemble
clusters don`t show much of a favorite until Saturday then 37% of
the clusters show support for the GFS solution with the low in the
Pacific Northwest.  This would support the deeper/further south
solution.

The tightening pressure gradient will bring breezy to windy
conditions on Friday and continued breezes on Saturday, especially
across the Columbia Basin, Gorge, Kittitas Valley, Yakima Valley,
Simcoe Highlands and Foothills of the Blue Mountains.  Ultimately,
where the low/trough set up will help determine how windy it may
get.  The ECMWF EFI is not excited about the wind gust potential on
Friday, and given the ECMWF more northerly track of the low it would
likely be less windy.  The NBm probabilities of winds >=39 mph range
from 70 to 100% in the above areas.  Given all the uncertainty
though, and the time range, things could change.  Probabilities of
winds >=47 mph are 40-60%, though higher in the Kittitas Valley.

Additionally, with the trough moving across the region, by Saturday,
temperatures will end up 5 to 10 degrees below normal.  Wednesday
will see highs slightly above normal, from near 80 degrees to the
lower 80s.  Thursday will be warmer with temperatures above normal
generally in the mid to upper 80s.  By Friday, the change starts
with highs ranging from the mid 70s to mid 80s.  Saturday will see
highs from the mid 60s to the mid 70s.  Sunday`s highs will be
similar to those on Saturday.

&&

.AVIATION...00Z TAFS.... There will be isolated SHRA/TSRA
around the region through the evening but not expected to
impact TAF sites. Skies will clear this evening then remain
mostly clear through Monday for overall VFR conditions.  Winds will
gust to around 25 kts at DLS/RDM/BDN before decreasing this evening
and becoming generally less the 10kts or less overnight. DLS
will see a return of breezy winds on Monday.



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  79  56  81 /   0   0   0   0
ALW  59  81  60  84 /   0   0   0   0
PSC  59  85  60  87 /   0   0   0   0
YKM  53  84  55  81 /  10   0   0   0
HRI  58  84  60  84 /   0   0   0   0
ELN  55  78  56  74 /   0   0   0   0
RDM  47  79  50  79 /   0   0   0   0
LGD  51  76  53  79 /  10   0   0   0
GCD  49  78  53  82 /  10   0   0   0
DLS  57  81  59  77 /   0   0   0   0

&&

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

$$

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