332
FXUS66 KPDT 262335
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
435 PM PDT Sun May 26 2024

Updated Aviation Discussion

.SHORT TERM...Tonight through Tuesday night...A ridge of high
pressure overhead will produce mostly dry, warm conditions with
light, diurnally driven winds through tomorrow morning.

The main weather concerns for the short-term period will develop
later tomorrow afternoon as the ridge axis shifts east over the
Rockies and an offshore trough of low pressure approaches from the
Pacific. This will turn flow aloft southwesterly and usher in
anomalous moisture across eastern Oregon and eastern Washington.
Ensemble systems advertise 125-175% of normal PWATs Monday
afternoon through Tuesday afternoon. While the best synoptic-
scale forcing will remain west of our CWA, a subset of CAMs in the
HREF suggest surface-based convection will develop over the
mountains of central Oregon (mainly east of the Cascades) Monday
afternoon. Gusty outflow winds will be possible with any activity
that does develop.

Monday evening through Tuesday morning, synoptic forcing
continues to increase as a mid- to upper-level jet moves eastward
into the PacNW. CAMs continue to produce a signal for a transition
to elevated convection, especially members such as the NSSL and
NAM Nest which historically handle these events better than, say,
the HRRR. Adding to confidence in elevated convection and a low
probability of lightning (10-20% chance) across portions of
central, north-central, and northeast OR into south-central WA is
ample mid-level (700-500 mb) moisture and negative Theta-E lapse
rates.

Tuesday afternoon, as the main trough, jet, and accompanying cold
front arrive, concerns shift to the potential for strong to severe
thunderstorms across portions of the Blue Mountains region.
Guidance is advertising 500-1500 J/kg of MLCAPE supported by mid-
level (700-500 mb) lapse rates of 7-8.5 C/km and surface dew
points in the mid-40s to mid-50s. Effective shear (EBWD)
of 40-50 kts, and low-level SRH values of 50-200 m2/s2 are
evident in latest guidance. Further highlighting the potential for
severe storms, the Convective Outlook from the SPC highlights a
Marginal Risk of severe thunderstorms for portions of Union and
Wallowa counties.

A second concern for Tuesday will be breezy to windy westerly
winds through the Cascade gaps and across the Columbia Plateau.
NBM probabilities highlight excellent chances (80-100%) of
exceeding 40 mph gusts and somewhat more modest chances (30-80%)
of exceeding 45 mph, so wind highlights may be needed. Plunkett/86

.LONG TERM...Wednesday through Sunday...A trough impacting the
region will continue to produce mountain showers Wednesday. The
best opportunity for activity will be over the Washington Cascades
(45-65%) chance, while the Blue Mountains keep a moderate chance
(30-40% through Wednesday evening. In addition to showers, gusty
winds are anticipated (75-95% chance for gusts of 35-45 mph),
mainly across the Columbia Basin. As the trough axis progresses
eastward, the opportunity for showers decreases, though a slight
chance (10-20%) remains over the higher peaks.

Building northwest flow on Thursday will help to usher showers
outside of the forecast area by the early evening. Winds of 10-15
mph will continue (60-80% chance) through Thursday, impacting
especially the Columbia River Gorge and the Kittitas Valley, with
lesser impacts spreading into Central Oregon as well.

An amplifying ridge is slated to move over the region on Friday,
keeping dry conditions, and aiding in the decrease of overall
winds. The degree of amplification varies from model to model,
as does the speed which the ridge moves through the forecast area.
This is the main period that shows variation in the cluster
analysis, with variations seen in strength and placement of the
ridge. Under its influence, warming temperatures, dry and calm
conditions will be present.

The next approaching Pacific system will approach the coast early
Saturday, with moisture spreading east. The Washington Cascades
are looking for a slight chance (10-20%) of showers by Saturday
evening. Moisture will progress further into the forecast area
through Sunday. By Sunday evening, there will be a moderate chance
(30-50%) of showers over the Washington and Oregon Cascades, and
a slight chance (15-25%) over the Blue Mountains.

Temperatures through the forecast period will begin around 5-10
degrees below normal under the first trough, but will warm to
around 5-10 degrees above normal by Saturday. Branham/76

.AVIATION...00z TAFs...VFR conditions to prevail through the
period. Mostly sct CIGS AOA 12kft AGL will continue to impact
sites through the period, except for bkn CIGS AOA 7kft AGL will
impact site YKM through the overnight hours. Winds will be light,
less than 12kts, at most sites through the period. Except site DLS
where winds of 12-15kts with gusts up to 25kts will continue
through 06Z tonight, becoming light afterwards. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  78  52  75 /   0   0  20  20
ALW  50  82  56  79 /   0   0  20  20
PSC  50  83  58  82 /   0   0  20  20
YKM  43  80  50  77 /   0   0   0  10
HRI  49  82  55  79 /   0   0  20  20
ELN  43  77  51  70 /   0   0   0  10
RDM  41  79  46  71 /   0   0  20  10
LGD  43  78  49  76 /   0  10  10  40
GCD  43  82  49  79 /   0  10  20  50
DLS  50  79  54  71 /   0   0   0   0

&&

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

$$

SHORT TERM...86
LONG TERM....76
AVIATION...82