616
FXUS66 KPDT 270532
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1032 PM PDT Wed Jun 26 2024

.UPDATED AVIATION...06Z TAFs...Primary concern for TAF sites
continues to be winds. Winds will vary overnight with all sites
returning to sustained winds of 10-20 kts by late morning with gusts
up to 30kts. Sky conditions will vary with mid to high levels clouds
overnight with some partial clearing followed by some mainly FEW-SCT
clouds.


&&

.PREV DISCUSSION... /issued 309 PM PDT Wed Jun 26 2024/

SHORT TERM...Today through Friday...

Bottom Line Up Front

1. Thunderstorms along the eastern mountains this afternoon.

2. Breezy to windy conditions today through the Cascades Gaps.

3. Dry and warm conditions return Thursday night.

Current radar shows that the thunderstorms have since decreased over
the east slopes of the Cascades from this morning. Some cells are
beginning to pop up over Wallowa but ground observations are
showing very lite rain as well as no lightning. Thunderstorms
will continue to develop along the eastern mountains with 30-50%
probabilities, highest probabilities in Wallowa County this
afternoon with orographic lifting assisting in the formation of
the cells over the mountains. The storms that do develop over
Wallowa County will put down some precipitation with model derived
soundings showing PWATs of 0.80 inches, MUCAPEs of greater than
200 J/kg, lifted index between -2 to -4 and lapse rates over 8.5
C/km.

Models are in firm agreement with the upper level low continuing to
push onshore. Clusters are showing no variances between the models
so the forecast outcome is pretty on par. Southwesterly flow
aloft will dominate through the remainder of today and continue to
tighten the cross Cascade pressure gradient. Looking at the
pressure gradient in office, the pressure gradient change between
PDX to GEG ranging from 9 to nearly 11 mb through 8 PM tonight.
Looking at the raw ensemble data it shows there to be over an 80%
probability of the Simcoe Highlands, lower Columbia Basin and the
southern foothills of the Blues to see gusts nearing and just
over 40 mph. Ground observations along those areas have already
confirmed the speeds already.

Models remain in firm agreement with alignment within the clusters
showing little to no variances in the track of the exiting low and
incoming ridge. To start, showers will affect mainly the mountains
as the upper level low continues to traverse across the area.
Ensembles show a 20% probability of 0.05 inches of rain along the
eastern slopes increasing steadily as you head towards the crests
with 60-80% chances of 0.05 inches of rain along Snoqualmie and
Stampede Passes. Probabilities of 0.05 inches along the Northern
Blues is less than 10%. Once the upper level low moves off towards
the east, and upper level ridge begins to build back over the
region. This will bring warming temperatures and dry conditions back
to the region. Thursday will also be the coolest day of the short
term with over 50% of the ensembles showing a 5 to 10 degree drop
from todays highs of upper 70s to mid 80s. Bennese/90

LONG TERM...Saturday through Wednesday...The main sensible
weather highlights include:
- Elevated fire weather conditions possible (50-70%) Sunday owing
  to the combination of dry and windy conditions alongside low
  chances for isolated thunderstorms in the eastern mountains.

- Broadly seasonable temperatures with Sunday and Wednesday
  looking to be more likely than not the warmest in the period.

The large scale pattern early Saturday will be characterized by a
somewhat progressive synoptic pattern. Guidance is in good
agreement with a shortwave trough moving in behind a transient
shortwave ridge early Saturday. The former associated with an
upper- level low in the eastern North Pacific offshore BC. This
feature will lift across the PacNW and move north into Alberta
to then be followed by another shortwave trough that will amplify
and deepen across the PacNW on Sunday. A weak marine push late
Saturday/Saturday night associated with the initial feature will
be followed by a stronger cold front crossing late Sunday/Sunday
Night. The latter day will support stronger, increased winds
along and ahead of the front. Increased confidence (~70%) with
clustering solutions showing good agreement, which support the
favorable combination of dry and windy conditions more so Sunday
compared to Saturday. Chances for 24-hr peak daily gusts exceeding
39 mph surpass 75% across Kittitas Valley, Simcoe Highland,
Cascade gaps, and the eastern Gorge spilling into north central OR
and parts of the foothills of the Blues. Most likely peak gusts (50th
percentile) are seen to be around 35-45 kts (40-50 mph) on Sunday.
Meantime, large scale forcing for ascent ahead of this impulse
with marginal instability and modest mid-level lapse rates will
support the potential for low-end (15-25%) storm chances confined
mainly to the eastern mountains Sunday. Limited instability on
Saturday but could see slight chances for showers across the upper
slopes of the WA Cascades and eastern mountains late Saturday and
Saturday night. Northwest and upper-level cyclonic flow dominates
Monday with breezy conditions likely to continue, albeit slightly
cooler with drier conditions more likely than not area-wide.

Thereafter guidance in moderate agreement between either near
zonal (50%) to a northwest flow regime with upstream ridging (50%)
taking hold offshore the PacNW on Tuesday. Nonetheless, a less
active pattern looks to take shape Tuesday and Wednesday with
highs starting to warm back up by midweek.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  52  73  48  79 /  10   0   0   0
ALW  56  77  53  83 /  10  10   0   0
PSC  58  80  54  84 /  10  10   0   0
YKM  51  75  48  81 /   0  10   0   0
HRI  57  79  52  84 /  10   0   0   0
ELN  52  71  50  81 /   0  10   0   0
RDM  45  72  41  79 /  10   0   0   0
LGD  50  69  45  78 /  20  10   0   0
GCD  50  73  45  81 /   0   0   0   0
DLS  56  74  53  84 /  10  10   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....80
AVIATION...90