243
FXUS66 KPDT 242126
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
226 PM PDT Sat May 24 2025

.SHORT TERM...Tonight through Monday Night...Weather is fairly quiet
and benign this afternoon as a large upper low in the Gulf of Alaska
is sending a southwest flow into the area and strengthening a ridge
over our area. The quiet weather should continue through the night
due to the high pressure over the area. Skies will be mostly clear
with some higher clouds increasing overnight. The building ridge and
a southwest flow will bring warmer air into the area and overnight
lows will warm 3 to 6 degrees from last night to the upper 40s to
mid 50s with 40s in the mountains.

On Sunday, the upper low will send a trough to a few hundred miles
off the Pacific Northwest coast. The ridge will remain overhead and
the southwest flow will lead to more warming and it will be quite
warm with highs in the Columbia Basin reaching the upper 80s to
lower 90s with upper 70s to mid 80s elsewhere. The NBM gives the
Columbia Basin a 40-60 percent chance of reaching 90. This is about
12 to 15 degrees above normal but still well below daily high
temperature records. An additional concern due to the southwest flow
will be moisture transport in the afternoon and a weak impulse in
the flow. Models show precipitable water amounts of 0.7"-1.0" from
central Oregon north into the Columbia Basin, which is 110-150
percent of normal. Most unstable CAPE values reach as high as 1000-
1500 J/kg in the Blue Mountains and 100-750 J/kg in central Oregon
and the Oregon portion of the Columbia Basin. Wind shear values of
25-30 kts will allow any storms to develop to have some organization
and ability to hold together for more than a few minutes, so
isolated to widely scattered thunderstorms are anticipated in the
late afternoon and evening over most of the area though chances look
limited east of the Blue Mountains. Storms are not expected to reach
severe levels but a few could get strong with brief gusty outflow
winds to 40 mph being the main concern though small hail is possible
as well. Thunderstorms will wind down in the late evening but
showers should linger overnight. Rain amounts will generally be
under a tenth of an inch though locations under thunderstorm paths
could get up to a quarter inch of rain. Afternoon winds in general
will be northwest at 10 to 20 mph with gusts to 25 mph though the
Columbia gaps will reach 15 to 25 mph with gusts to 35 mph.
Overnight lows Sunday night will be a few degrees cooler in central
Oregon as skies start clearing out late while the rest of the area
will be up a few degrees due to the mostly cloudy skies. Lows will
be in the mid to upper 50s in the Columbia Basin and in the 40s
to around 50 elsewhere.

By Monday, the trough will be centered overhead in the afternoon and
the ridge will have moved off to the Rockies. Cooler air will move
in with the trough and temperatures will drop 10 to 14 degrees from
Sunday with highs in the 70s and mainly mid to upper 60s in the
mountains. The atmosphere will be more stable, so am expecting just
a chance of showers over the mountains tapering off in the late
afternoon. Would not be shocked to see a thunderstorm or two over
the eastern mountains, though the NBM keeps chances under 15
percent, so have left thunder out of the forecast. Rain amounts will
be less than a tenth of an inch though the higher portions of the OR
Cascades, Ochoco and Elkhorn Mountains could get up to two tenths of
an inch. Afternoon winds will again be breezy, but a few mph slower
than on Sunday. Sunday night will see the wave moving off to the
east, though the main upper low and trough will remain offshore and
begin building a new ridge in the overnight hours. Lows will still
be cooler and in the 40s with some upper 30s in the mountains.
Perry/83


.LONG TERM...Tuesday through Saturday...An area of upper level
ridging will begin the long term, initiating dry/warm conditions
for the CWA and most of the PacNW in general (>90% confidence).
Ridge will last until around first half of Thursday, where a
shortwave will develop briefly, allowing for light mountain
showers to develop late Thursday afternoon heading into the early
evening hours. QPF amounts remain non- significant as this system
remains relatively dry with most areas in the Blues receiving up
to 0.10" and the peaks receiving up to 0.20" (50-70% confidence
for both intervals). Basin and Central OR remain dry heading into
mid to late week. Models and clusters remain fairly confident that
ridging immediately builds back-in by Friday, ensuring the rest
of the long term remains dry and clear.

After the trough passage, the warming trend continues on heading
into next weekend, as the ridge builds more energy and heats up the
CWA following clear skies and light diurnal winds. Need to monitor
trends heading into next weekend as confidence is moderate (40-60%)
at this point that we will see our hottest temperatures of the year
in this period. Highs at this point are showing above average
temperatures mostly in the 15-20 degree range with some areas
reaching up to 22 degrees above normal on Saturday. Current NBM
graph is displaying low to mid 90s for the Columbia Basin and high
80s for higher elevated population areas Saturday. Regardless,
expect hot temperatures after the shortwave passage and the build of
up heat going into the weekend. 95


&&

.AVIATION...18Z TAFs...Nothing forecasted to bring any
site below VFR criteria. Satellite shows a band of high cirrus
clouds aloft in the CWA. The weather pattern supports dry
conditions with light and variable winds for the next 24 hours. No
CIG or VIS impacts expected at well during the 18Z period. 95



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  53  86  55  74 /   0  10  50  20
ALW  55  87  57  74 /   0   0  50  30
PSC  51  91  57  80 /   0   0  60  10
YKM  53  87  55  77 /   0   0  50  10
HRI  53  89  57  79 /   0   0  50  10
ELN  51  86  52  73 /   0  10  50  10
RDM  46  82  45  71 /   0  20  40  10
LGD  49  84  52  70 /   0  10  40  20
GCD  50  87  50  72 /   0  10  60  20
DLS  55  79  54  73 /   0   0  40  10

&&

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

$$

SHORT TERM...83
LONG TERM....95
AVIATION...95