864
FXUS66 KPDT 221741
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1041 AM PDT Thu May 22 2025


.Updated Aviation Discussion.

.AVIATION...18Z TAFS...VFR conditions currently at all sites, with
the exception of KRDM which is experiencing MVFR conditions due to
reduced ceilings of 15-25kft. These ceilings will improve shortly as
VFR conditions persist for all sites through the remainder of the
period. Light rain is expected to occur late this morning over KALW,
with dry conditions across all terminals through the day. Winds at
KRDM and KBDN will be breezy with gusts between 15-20kts this
afternoon, but will stay below 10 kts elsewhere. 75


&&

.PREV DISCUSSION... /issued 440 AM PDT Thu May 22 2025/

SHORT TERM...Today through Saturday...Nighttime satellite and
radar imagery shows a shortwave trough lifting a west-east
oriented band of showers across far northern OR and southern WA,
while partly cloudy skies have developed across the southern
third of the forecast area.

A shortwave trough will continue to slide across the PacNW today
while splitting into two distinct waves, with the stronger vort
max associated with this system skirting just south of the
forecast area; the weaker of the two shortwaves will meander
across the southern half of WA. The current band of showers will
continue to gradually lift north across the forecast area this
morning, but will take on a SW to NE orientation as the shortwave
trough pushes further inland into the early afternoon. CAMs are
favoring some potential clearing across portions of the Blues,
Strawberrys, and Wallowa county early in the afternoon, which
would allow for weak instability to develop in these areas. This
will result in a slight chance (15-20%) of isolated thunderstorms
to develop across the aforementioned areas this afternoon into the
early evening. Both shortwaves will exit the forecast area late
this evening, with shower activity area-wide coming to an end
before midnight.

Friday, a relatively weaker and drier shortwave trough will move
across the western CONUS, with the main shortwave energy
associated with this system staying well to the south of the
PacNW. Nonetheless, increasing surface instability into the
afternoon will combine with weak lift from the passing shortwave
to result in slight chances (15-25%) of light showers and isolated
thunderstorms. As daytime heating comes to a close and the
shortwave trough exits the region into the evening hours, shower
activity will diminish area-wide. Through Friday evening, the best
chances for accumulating precipitation will be confined to the
mountain areas, where there is a 55-70% chance that the Cascade
crest and eastern mountains will see at least 0.1 inches of
rainfall in a 48-hour period.

Saturday, upper level ridging will build into the PacNW with dry
and quiet conditions. The region will see temperatures about 5 to
10 degrees warmer than Friday, with a 70-80% chance that
temperatures will exceed 80 degrees in the Columbia Basin/Gorge,
Yakima valley, and the John Day Basin. Lawhorn/82

LONG TERM...Sunday through Wednesday...Sensible weather concerns
through the extended forecast will revolve around the passage of
an upper shortwave trough that will trigger shower and isolated
thunderstorm activity across the region late Sunday through
Monday. Confidence in forecast beyond Monday wanes as disagreement
amongst ensemble members grows in regards to potential
ridging/troughing influencing the region.

Upper level ridging will persist across the PacNW into Sunday,
with the ridge axis pushed into the northern Rockies by an upper
trough offshore. A warming trend will continue through Sunday
afternoon as well, with temperatures in the mid to upper 80s in
the lower elevations and a 45-55% chance that the Columbia Basin
warms into the 90s. Increased daytime heating and a developing
southwest flow aloft will help in increasing surface instability
across much of central and northeastern OR as well as along the
northern Blue mountains/foothills in WA for Sunday afternoon. As a
result, a slight chance (15-25%) of isolated thunderstorms will
be possible across the aforementioned areas Sunday afternoon into
the evening. Ensemble cluster guidance is in decent agreement
that shower activity will continue overnight Sunday into Monday as
the shortwave trough lifts across the PacNW. About 60% of
ensemble members do favor weak CAPE values (100-250 J/kg)
redeveloping over the eastern mountains and portions of central OR
Monday afternoon, providing another afternoon/early evening of
isolated thunderstorm chances (10-20%).

Tuesday into the middle of next week, ensemble guidance comes into
disagreement on whether upper level ridging building back into
the region will keep shortwave trough features offshore or not.
Light convective showers and isolated thunderstorms are still
favored each afternoon over the eastern mountains and OR Cascade
crest, but ~40% of ensemble members indicate more widespread
shower chances into Wednesday with a trough passage. At the
moment, overall confidence in forecast beyond Monday is low
(15-25%), though low-mod confidence (25-35%) that isolated
thunderstorm/shower activity will develop in the afternoons over
mountain zones. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  68  44  73  46 /  40  10   0   0
ALW  67  47  73  49 /  50  10   0   0
PSC  72  46  78  46 /  30   0   0   0
YKM  71  46  76  47 /  40   0   0   0
HRI  71  46  77  47 /  30   0   0   0
ELN  68  44  72  45 /  30  10   0   0
RDM  64  39  71  39 /  20   0   0   0
LGD  63  41  70  42 /  60  10  10   0
GCD  66  40  72  41 /  50  10  20  10
DLS  71  48  75  47 /  50   0   0   0

&&

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

$$

SHORT TERM...82
LONG TERM....82
AVIATION...75

NWS PDT Office Area Forecast Discussion