055
FXUS66 KPDT 252351
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
451 PM PDT Fri Apr 25 2025

.Updated for Aviation...



SHORT TERM...Today through Sunday night...An upper-level low that
is currently just offshore of northern California will drive
shower and thunderstorm chances this afternoon and Saturday
afternoon as it slowly pushes inland over the Great Basin region
through the forecast period. Tangible weather transitions to
breezy to windy westerly winds through the Cascade gaps,
especially the eastern Columbia River Gorge and Kittitas Valley
late Saturday through Sunday as cross-Cascades pressure gradients
tighten in response to an incoming shortwave and cross-Cascade
temperature gradient (warm east side, cool west side).

This afternoon and evening, shower and thunderstorm chances will
ramp up across the southern portion of our CWA, primarily in
central OR, the Ochoco-John Day Highlands, and portions of the
southern Blue Mountains. Convection is ongoing in southeast OR,
and isolated activity has developed in Klamath County. Through
this afternoon, additional development is likely (75% chance)
across central and southeast OR. Storm motion will generally be
northwest to west. Farther north across the southern Blue
Mountains and portions of the northern Blue Mountains and Wallowas,
more isolated showers and thunderstorms will be possible, but
unlikely to be more than isolated to scattered (10-30% chance of
showers, 5-14% chance of thunder).

Saturday, CAMs are advertising an earlier start to convection
(12-1PM PDT), for most of the Blue Mountain region. The highest
chance of thunderstorms will be along the eastern edge of our CWA
in Grant, Union, and Wallowa counties.

This afternoon and Saturday, weak effective shear (generally 10-20
kts) should keep the threat of severe storms low (<2% for all
hazard types from SPC`s daily outlooks).

Late Saturday through Sunday night, winds will increase in
magnitude from the west. NBM probabilities currently suggest a
good chance (widespread 50-70%, locally higher) of advisory-level
wind gusts through the eastern Columbia River Gorge and Kittitas
Valley, and portions of the lower Columbia Basin of Oregon, north-
central Oregon, the Simcoe Highlands, and the foothills of the
southern Blue Mountains.

Lastly, the warm temperatures will lead to some river rises, with
the Naches River at Cliffdell currently forecast to reach action
stage Saturday through the remainder of the forecast period.
Plunkett/86

LONG TERM...Monday through Friday...

Key Messages:

1. Widespread showers Monday evening through Tuesday morning.

2. Breezy winds Monday and Tuesday afternoon/evening.

3. Elevated river levels through the week.
   *Hydrologic Statement Issued*

The extended period is characterized by an upper level shortwave
trough Tuesday that will be followed by an upper level ridge that
will continue through the remainder of the week. This will lead to
widespread rainfall beginning along the Washington Cascades
Monday evening before including the Oregon Cascades overnight and
extending across the Basin through the early morning hours on
Tuesday. Rain is expected to linger across the Washington Cascades
and the eastern Mountains through the afternoon. Rain amounts of
0.10-0.20" are likely over the northern Blue Mountains, 0.05-0.10"
across the Blue Mountain foothills and the John Day Basin, and
0.01-0.05" through the Lower Columbia Basin and Central Oregon.
Confidence in these rain amounts is currently moderate 50-60% as
59% of ensemble members advertise slightly less rain amounts
Monday evening through Tuesday afternoon as associated with a
weaker incoming upper level shortwave trough, which is more
favored by the ECMWF solution. The variance between ensembles is
currently rather low, +/-0.03", hinting at the overall difference
in shortwave trough strength being minor between ensembles and
deterministic guidance.

The approaching system will also lead to elevated winds across the
east slopes of the Washington Cascades, Gorge, Southern Blue
Mountain Foothills, Simcoe Highlands, and Kittitas Valley
associated with a pressure gradient developing along the Cascades
on Monday and the passing shortwave on Tuesday. West- northwest
sustained winds of 15 to 25 mph with gusts up to 40 mph will be
possible both days across the aforementioned areas. Confidence in
these wind values is moderate to high (60-70%) as the NBM suggests
a 50-70% chance of gusts reaching 40 mph or higher both days and
a 20-40% chance of reaching advisory-level criteria (45 mph gusts
or greater). The best chance (40% chance) for winds reaching
advisory-level resides across the Kittitas Valley Monday, with
chances dropping slightly (33%) Tuesday. The more moderate to high
confidence with winds is associated with the lack of large
variance between ensemble members and deterministic guidance. Even
though there is slight differences between shortwave strength,
this only results in 55% of ensemble members hinting at a 1-4 mph
increase in winds - which is primarily focused over the Kittitas
Valley.

Warm and above normal temperatures coupled with incoming
precipitation this weekend and into the early part of the workweek
has attributed to elevated river levels, with the Naches River
near Cliffdell forecast to reach action stage Saturday at 11 AM
and continuing to stay in action stage through the remainder of
the week. As a result, a Hydrologic Statement has been issued as
there is a greater than 95% chance of reaching action stage and
less than a 5% chance of reaching Minor Flood Stage. Temperatures
will stay above normal through the week, cooling 3 to 5 degrees
Monday to Tuesday behind the passing upper level shortwave. A
warming trend then unfolds through the remainder of the workweek
as upper level ridging moves into the Pacific Northwest and
southwest flow develops into Thursday. These synoptic features
will allow high temperatures to break into the low 80s across
lower elevations of the Columbia Basin starting Thursday. 75

AVIATION...00Z TAFS...
VFR conditions are expected through the TAF period. Latest radar
showed some SHRA mainly south and east of BDN and RDM. These SHRA
could impact both locations through the evening hours. There is
also a low (<20%) chance of a TSRA at either location through the
evening. The other TAF sites are expecting nothing more than a
passing shower, if that.

Winds will be mainly 10 kts or less except for DLS, which will
have gusty winds 20 to 25 kts through the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  74  45  69 /  10  10   0   0
ALW  50  72  48  69 /  10  10   0   0
PSC  47  80  46  76 /   0   0   0   0
YKM  49  80  46  75 /   0   0   0   0
HRI  48  79  46  73 /  10  10   0   0
ELN  48  75  47  68 /   0   0   0   0
RDM  43  69  35  63 /  50  20   0   0
LGD  48  69  44  65 /  20  30  10  10
GCD  46  66  42  65 /  70  60  20  10
DLS  51  72  44  65 /  10   0   0   0

&&

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

$$

SHORT TERM...86
LONG TERM....75
AVIATION...77