516
FXUS66 KPDT 112248
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
348 PM PDT Mon May 11 2026

.KEY MESSAGES...

- High temperatures in the upper 80s to mid 90s Tuesday

- Isolated thunderstorms along elevated terrain in central and
  eastern OR Tuesday afternoon into the overnight hours

- Mountain showers, isolated mountain thunderstorms, and breezy
  to gusty low elevation winds Wednesday

&&

.DISCUSSION...
Tonight through Tuesday: Little to talk about on satellite this
afternoon as skies are mostly clear with very thin cirrus decks
moving across the forecast area.

Clear conditions and light winds today will continue overnight
into tomorrow as an upper level ridge persists over the region.
By late tomorrow morning, the upper ridge will begin to
break down and push east, with deep southerly flow developing
as a result. Instability across elevated terrain of central and
eastern OR will increase as a result (MUCAPE 250-1250 J/kg),
introducing a low chance (<10%) of isolated thunderstorms in
these areas into the afternoon. CAMs and deterministic guidance
are showing a shortwave impulse with a weak moisture plume
riding up the southerly flow late Tuesday afternoon through the
overnight hours. The combination of the shortwave, moisture, and
instability will result in a continued low chance (10-15%) of
isolated thunderstorms across the elevated terrain of central
and eastern OR through Tuesday night. The upper ridge and
southerly flow aloft will also result in temperatures climbing
into the upper 80s to mid 90s Tuesday afternoon.

Wednesday and Thursday: Guidance has come in much better
agreement in the last 24 hours in an upper low offshore kicking
inland Wednesday morning, which will transition into an open
trough with a slight negative tilt. There is high confidence
(80-90%) that the trough passage will bring mountain shower
chances and cooler temperatures across the region Wednesday,
while there is mod-high confidence (65-85%) that widespread
winds 20-35 mph with gusts 35-55 mph will develop across the
lower elevations. The strongest winds are expected through the
Columbia Basin/Gorge and adjacent valleys/foothills, including
north central OR and the Simcoe Highlands...mod-high confidence
(70-85%) that wind advisories will be needed in most of these
areas Wednesday.

While guidance is in mostly good agreement, there remains
uncertainty on timing of the trough crossing inland, which
will impact the extent of isolated thunderstorm chances for
Wednesday morning through the afternoon. If the trough lags and
comes in later in the morning, then areas from OR Cascades to
the eastern mountains will see slight chances (~15%) of isolated
thunderstorms embedded with shower chances, whereas if the
trough arrives earlier the isolated thunderstorm chances will be
limited mainly to the elevated terrain of northeast OR.
Confidence on forecast thunderstorm extent is moderate (50-65%).

Ensemble cluster guidance is in great agreement of a broad flat
ridge developing behind the trough exit late Wednesday through
Thursday, resulting in shower chances being limited to the
Cascade crest. Otherwise, breezy winds will continue in the
lower elevations throughout Thursday.

Friday through Sunday: Ensemble cluster guidance is in good
agreement through the weekend that a broad upper trough will
slide over the PacNW, producing another round of mountain
showers with breezy winds in the lower elevations (confidence
45-60%). By Sunday, there is decent agreement in the forecast
area sitting between an upper ridge to the northwest and upper
trough to the east, keeping the lower elevations dry with
locally breezy winds and light showers across the Cascades and
northern Blues.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
VFR conditions are forecast for all sites over the next 24
hours, with cloud cover ranging from SKC to SCT250. Winds will
be diurnally and terrain-driven, predominantly 10 kts or less
with periodic afternoon gusts. By Tuesday evening, just beyond
the TAF period, an incoming low-pressure system will induce a
low (5-15 percent) chance of high-based showers and
thunderstorms to Oregon sites, especially BDN/RDM.

&&

.FIRE WEATHER...
Dry and warm conditions continue through Tuesday. A breakdown
in high pressure aloft will bring increasing unstable conditions
Tuesday afternoon and night, with a low chance (<15%) of
isolated thunderstorms in central and eastern OR. Breezy to
gusty westerly winds in the lower elevations and mountain
showers will develop Wednesday. Isolated thunderstorms will be
possible Wednesday morning into the afternoon. Breezy winds and
isolated mountain showers continue Thursday. Lawhorn/82

&&

.Preliminary Point Temps/PoPs...
PDT  48  85  52  68 /   0   0   0  60
ALW  51  87  56  69 /   0   0   0  70
PSC  50  90  56  73 /   0   0  10  50
YKM  50  86  55  72 /   0   0  20  40
HRI  48  87  54  70 /   0   0  10  50
ELN  45  82  49  65 /   0   0  30  60
RDM  45  90  43  63 /   0   0  40  60
LGD  45  91  51  67 /   0   0   0  80
GCD  47  94  49  68 /   0   0  10  80
DLS  53  88  54  68 /   0   0  40  50

&&

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

&&

$$

DISCUSSION...82
AVIATION...86
FIRE WEATHER...82