442
FXUS66 KPDT 200958
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
258 AM PDT Sun Apr 20 2025

.SHORT TERM...Today through Tuesday...Nighttime satellite imagery
tonight shows mostly clear skies east of the Cascades, with
stratus decks banking up against and just over the WA Cascades and
northern OR Cascades. Meanwhile, water vapor imagery shows broad
troughing situated just north of the PacNW, with a shortwave
traveling south along the BC coastline.

Today, the upper trough will dip south into the PacNW and will
guide the shortwave across the region, resulting in increasing
showers across the Cascades later this morning. As the shortwave
rounds the bottom of the trough, rain/snow showers will increase
across the northern Blue mountains/foothills, Strawberry Mountains,
and across Wallowa county in the afternoon and evening. Overnight,
snow levels will drop to between 3.5kft to 4kft, allowing for
modest snow accumulations across the interior northern Blues
(35-45% chance for 4 inches of snow), with lighter amounts(less
than 2 inches) along the Cascade crest. Continued cold air
advection and the shortwave passage will also prevent surface
pressure gradients from weakening across the area. This will
result in breezy west to northwest winds continuing to pass
through the Cascade gaps and into the Columbia Basin, adjacent
valleys, and central OR (30-45mph gusts for the Cascade Gaps and
20-35mph for the Columbia Basin).

The upper trough will move east of the region Monday with shower
chances diminishing across the mountains by the afternoon as a
dry northwest flow develops aloft. Cold air will continue to
filter into the region under the flow aloft, which will keep
pressure gradients at the surface tightened for yet another day.
Breezy west to northwest winds will continue through the Cascade
gaps(30-40mph gusts) with breezy to locally breezy winds in the
lower elevations(20-30mph gusts).

Dry and cool conditions will continue across the region Tuesday
while a moisture starved shortwave trough swings through the
PacNW. By Tuesday morning, surface pressure gradients are
anticipated to weaken, resulting light to locally breezy
conditions across the forecast area through the afternoon. By the
evening hours, breezy winds will redevelop through the Cascade
gaps as the shortwave trough axis passes east of the region.

The continued troughing pattern impacting the forecast area will
result in daily afternoon temperatures in the upper 50s to mid 60s
across the lower elevations...40s to mid 50s mountains and
mountain valleys. Lawhorn/82


.LONG TERM...Wednesday through Sunday...Models are coming into much
better agreement on the synoptic pattern through next weekend. The
midweek continues to look quiet with ridging overhead, with the
weekend looking wet with a broad low encompassing the region
starting around Friday. Disagreement still exists as to where the
center of this low will track, which will ultimately determine our
precipitation forecast, but compared to 24 hours ago, forecast
confidence has increased quite a bit.

We`ll see our warmest temps of the period midweek with a high
pressure ridge overhead. Lowlands look to warm well into the 70s by
Thursday, before a pattern shift occurs on Friday as SW flow moves
in ahead of the aforementioned low. The deterministic GFS shows more
of a closed low with a slower approach, while the ECMWF shows more
of an open trough that moves quicker through the western CONUS.
Ensemble clustering is split pretty evenly on solutions, however
both would provide a shot of precip to the forecast area. The GFS
solution would be wetter, with stronger downslope winds across the
foothills of the Blues and the Grande Ronde Valley, while impacts
with the ECMWF solution would be lighter. Don`t usually see the
ensembles this evenly split with their solutions, but until they
better converge on a solution, can really only broadly advertise a
precip threat over the weekend before really dialing in on potential
impacts or precip amounts.

Ensembles suggest a benign pattern behind this weekend system,
however if the GFS solution verifies, this low will be stubborn to
leave the forecast area, making for continued precip chances with
relatively cool temps, with the caveat that any lingering precip
amounts would be light. Either way, Friday and Saturday look to be
the most active days of the period at this time. Evans/74


&&

.AVIATION...12z TAFs...VFR conditions expected. Winds will once
again pick up in the late morning/early afternoon for all sites,
gusting up to 25 kts out of the W and NW, with the strongest gusts
expected for PDT and DLS. Clouds will build through the morning,
becoming sct-bkn at mid-levels, before lower few-sct cigs develop
heading into the evening, especially for PDT and ALW. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  39  59  33 /  10  10   0   0
ALW  61  41  59  36 /  10  40  20   0
PSC  65  42  65  37 /  10  10   0   0
YKM  63  36  63  35 /  10  10   0   0
HRI  64  41  63  36 /   0  10   0   0
ELN  57  36  56  34 /  10  20   0   0
RDM  59  30  60  29 /   0   0   0   0
LGD  59  36  55  30 /  10  30  10   0
GCD  61  36  58  31 /  10  10   0   0
DLS  61  43  61  39 /  10  10   0   0

&&

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

$$

SHORT TERM...82
LONG TERM....74
AVIATION...74