120
FXUS66 KPDT 080257
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
757 PM PDT Fri Jun 7 2024

.EVENING UPDATE...Mid- and upper-level water vapor imagery shows a
distinct shortwave tracking east-northeast across central OR this
evening. This wave, in conjunction with RAP-analyzed MLCAPE of
500-100 J/kg and sufficient surface and mid-level moisture likely
facilitated the initiation of convection over the higher terrain
of northern Klamath and Lake counties and southern Deschutes
County this afternoon. As the shortwave tracks eastward this
evening, synoptic and orographic support will continue to support
a slight chance (15%) of showers and a very slight chance of
isolated thunderstorms (5-10%) across far southern Deschutes,
Crook, and Grant counties over the next couple hours. Plunkett/86

&&

.AVIATION...06z TAFs...VFR conditions expected for the period.
Winds will remain light to moderate out of the north and east,
with skies clear overnight. Clouds will then start to build in by
late Saturday morning as moisture pushes into the forecast area.
Once again, there will be a slight chance of showers and
thunderstorms around BDN and RDM, but overall expectation at this
time is that the majority of shower activity will remain south of
both sites. Evans/74

PREV DISCUSSION... /issued 211 PM PDT Fri Jun 7 2024/

SHORT TERM...Today through Sunday...

Bottom Line Up Front (BLUF)

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

2. Warmer than average temperatures through the short term with
hottest day Saturday.

3. Winds increase again Sunday.

Hi-res models are in decent agreement with the upper level
synoptic pattern through Saturday. An upper level ridge is in
place over the region and will begin to flatten slightly as the
leading edge of an upper level trough makes its way towards the
PacNW. 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 the eastern
mountain steadily increasing in probabilities each day. The SPC
has a general thunderstorm outlook over the southern portion of
the CWA both today and Saturday then it switches to along the
eastern mountains on Sunday. Model derived soundings across the
eastern mountains, MUCAPE values will be 200-300 J/kg through
Deschutes County with lapse rates of 7.9 C/km, lifted index of
-2, PWATs of 0.7 inches and bulk shear near 20 kts. While these
 ingredients are present, confidence in thunderstorm chances are
 low of Deschutes County with less than 15%. As the upper level
 trough continues to push onshore, thunderstorm ingredients are
 projected to increase as well as begin to move along the Ochoco-
 John Day Highlands. Model derives sounding again show MUCAPE of
 250-350 J/kg, lapse rates of 8 C/km, lifted index of -2 to -3,
 PWATs of 0.85 inches and bulk shear nearing 25-35kts. This
 increases thunderstorm probabilities to 20% Saturday. Lastly,
 thunderstorm probabilities increase Sunday to 25-30% and shift
 along the entire eastern mountains and highlands as well as the
 WA Cascade crests. MUCAPE increase to 400 J/kg and even higher
 values of 600 J/kg through the Wallowa mountains with lapse rates
 cresting 9 C/km, lifted index of -4, PWATs nearing 0.9 inches
 and bulk shear of 35 kts. Confidence in these storms becoming
 severe is low, less than 5%.

With the upper level ridge in place over the region through
Saturday and the incoming frontal boundary and upper level
trough, temperatures are going to remain above average through the
short term period. 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 increasing across portions of WA Saturday and
leveling back to near normal on Sunday. Over 50% 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 upper 80s and the
higher terrains will be in the mid 60s. Saturday, the hottest day
of the period, 80% of the raw ensembles are showing the majority
of the region to be in the upper 80s to low 90s, mid level
terrains in the mid to upper 80s and the higher terrains in the
upper 60s. 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 60% 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. There is an enhanced heat risk on Saturday
of 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. Due to
this, ensembles are picking up on increased winds, especially
through our wind prone areas. There is over a 55% chance the
Simcoe Highlands and portions of the Gorge seeing winds of 25 mph
or greater, 50-70% through the lower Kittitas Valley and less than
25% along the foothills of the Blues. Bennese/90

LONG TERM...Monday through Friday night...

Key Messages:

1. Cooling period during this week.

2. Breezy to locally windy conditions throughout this week.

As the transient ridge exits eastward Monday, the PacNW enters a
zonal pattern Tuesday through Wednesday. A short-lived ridge will
build in Thursday followed on Friday by a trough moving into the
PacNW. This trough is driven by the upper low centered over the BC
coast, bringing a cooling period across the region this week.
This would result in seasonable temperatures through the weekend
(>60% confidence). Precip could occur along the crest of Cascades
Friday once the trough moves over the PacNW (20-30% confidence).
Otherwise, there will be no significant weather impacts for the
extended period.

There is a high chance for windy conditions at Yakima Valley,
Simcoe Highlands, and Kittitas Valley during this period at
25-35 mph (>70%). The wind gusts could exceed up to 40 mph mainly
in the Kittitas Valley and Simcoe Highlands, but confidence is low
(<20%). The surface pressure gradient remains strong as this
progressive pattern persists. Breezy winds will be across for the
remaining PacNW at around 17-25 mph (>50% confidence). Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  53  87  59  82 /   0   0   0  20
ALW  53  90  61  84 /   0   0   0  20
PSC  56  92  63  88 /   0   0   0  10
YKM  57  89  59  86 /   0   0   0  10
HRI  56  92  62  88 /   0   0   0  10
ELN  52  88  60  82 /   0   0   0  10
RDM  52  85  56  80 /   0  10  20  10
LGD  50  84  58  77 /   0   0  10  30
GCD  55  88  57  80 /   0  10  30  50
DLS  62  89  63  84 /   0   0   0  10

&&

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

$$

EVENING UPDATE...86
SHORT TERM...90
LONG TERM....97
AVIATION...74