073
FXUS66 KPDT 241118
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
418 AM PDT Sat May 24 2025

Updated Aviation Discussion

.SHORT TERM...Today through Monday...Very little noteworthy on
nighttime satellite imagery tonight as upper level ridging builds
across the PacNW. That said, bands of thin cirrus rounding the top
of the ridge are spreading southeast across the forecast area.

An upper level ridge of high pressure will build over the region
today into Sunday, with dry conditions persisting through Sunday
morning. Temperatures will be warming during this period as well,
with widespread 80s developing across the lower elevations. In
fact, portions of the Columbia Basin will see a 50-75% chance of
reaching 90 degrees by Sunday afternoon.

Sunday, an upper level trough amplifying upstream will direct a
deep south to southwest flow over the PacNW. This will allow for
plenty of moisture transport into the region, with PWATs
increasing to 0.7 to 1 inch by Sunday afternoon. A shortwave
embedded in the flow will lift across the forecast area Sunday
afternoon and overnight, resulting in widespread shower chances
developing (35-70%). Isolated to widely scattered thunderstorm
chances (15-30%) will also develop in the afternoon and evening
hours, as surface CAPE values will be increasing to around 500-700
J/kg, low to mid level lapse rates steepen, and 0-3km shear
between 35-50kts develops across portions of the forecast area.
The most favorable areas of instability and shear will be focused
from central OR to the eastern mountains, with modest instability
parameters across the much of the forecast area. An attendant cold
front with the trough offshore will also approach the region
Sunday, resulting in an increasing pressure gradient across the
Cascades. This will result in breezy winds (gusts 30-40mph)
developing through the Cascade gaps in the afternoon, then
spilling into the Columbia Basin overnight.

The upper trough and cold front will push inland by Monday
morning, with shower activity continuing area-wide through this
time frame. This system will quickly exit to the east by Monday
evening, resulting in shower activity diminishing in the lower
elevations by the afternoon, then the mountains by Monday night.
BY Monday afternoon, the best instability parameters will be east
of the forecast area, however, enough surface instability will be
present for slight chances (15-20%) of thunderstorms across the
far eastern mountains and Wallowa county. Surface pressure
gradients will remain tightened during the front/trough passage
Monday, allowing breezy winds (gusts 25-40mph) to continue through
the Cascade gaps and into the Columbia Basin. Lawhorn/82

.LONG TERM...Tuesday through Saturday...Sensible weather concerns
through the extended forecast will revolve around upper level
ridging building over the region into the midweek, followed by an
upper trough passage that will produce light showers across the
mountain zones.

Upper level ridging will build back over the PacNW starting
Tuesday, with ensemble guidance in good agreement that the upper
ridge will remain over the forecast area through the first half of
Wednesday. Conditions will remain dry across the forecast area
with temperatures warming back into the mid to upper 80s
(confidence 60-75%), with moderate confidence (40-60%) that
portions of the Columbia Basin will hit 90 degrees again by
Wednesday afternoon.

Late Wednesday through Thursday, ensemble cluster guidance is in
good agreement of a shortwave trough moving across the PacNW, with
shower activity developing as a result. However, timing and
strength differences continue between each cluster solution, with
~40% of members producing light showers by Wednesday night across
central OR, and the remainder of the members favoring dry
conditions. By Thursday, members are all in favor of shower
activity developing with the trough passage, though only 23% of
members favor widespread showers as opposed to shower activity
limited to the mountains. Overall, confidence is higher (50-65%)
in shower activity developing Thursday rather than Wednesday, as
well as being confined mainly to mountain zones.

Late Thursday into the weekend, there us great agreement amongst
ensemble members that upper level ridging will build over western
CONUS, promoting a drying and warming trend into next weekend.
Lawhorn/82

.AVIATION...12Z TAFS...VFR conditions to prevail through the
period. Thin bands of cirrus will continue to bring CIGs of few-
sct AOA 25kft through the period. Winds will be light, 12kts or
less, at all sites. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  81  52  88  54 /   0   0   0  40
ALW  81  55  89  56 /   0   0   0  40
PSC  84  50  92  58 /   0   0   0  50
YKM  83  53  88  56 /   0   0   0  40
HRI  85  53  91  57 /   0   0   0  50
ELN  81  52  87  51 /   0   0   0  50
RDM  83  46  84  46 /   0   0  20  40
LGD  78  48  86  51 /   0   0  10  30
GCD  81  49  88  50 /   0   0  10  60
DLS  84  55  82  55 /   0   0   0  40

&&

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

$$

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