154
FXUS66 KPDT 122157
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
257 PM PDT Wed Jun 12 2024

.SHORT TERM...Tonight through Friday...The main sensible weather
concerns are limited in the short term with generally fair, near
seasonable conditions. The main highlights include:

- Breezy Friday with cooler temperatures as much as 10 degrees
  cooler than Thursday
- Dry conditions with partly to mostly sunny skies

A upper-level ridge will continue passing over PacNW today through
Thursday as the closed low moves towards to the BC coastline by
Thursday night. Near-seasonable temperatures, light winds, and
clear skies are favorable for today with no chances of precip.
However, breezy conditions are possible for Kittitas Valley and
Columbia River Gorge with wind gusts between 20-30 mph early tonight.
Confidence around 60% in these winds (moderate) with the surface
pressure gradient decreasing overnight. Cloud coverage begin to
increase Wednesday night for Kittitas Valley and more for Simcoe
Highlands and portions of the WA Cascades Thursday. HREF suggests
mid to high clouds would be passing through thus increasing
confidence (>70%). Temperatures warm up again tomorrow as the
upper ridge continues building eastward to The Rockies. Wind gusts
could return tomorrow night for Simcoe Highlands and some
portions of central OR up to around 20-25 mph (30-40% confidence).

Upper-level cyclonic flow will be in place early tomorrow night as
an closed upper low offshore British Columbia evolves moving east
to the near shore waters by Friday with modest 500 hPa height
falls spreading across the area. This will coincide with an
sharpening cross-Cascade gradient with increasing 700 mb and 850
mb winds moving into the region Friday as a weak front moves east
across the area early during the day. This will promote increasing
winds at the surface starting tomorrow night. Current thinking is
the strongest winds will be early Friday and over the Kittitas
Valley. Moderate to high confidence in frequent gusts reaching at
least 30 mph with the highest chances (>80%) occurring across the
Kittitas valley, elsewhere Lower Chances (>40-80%). Current
thinking is gusts will likely stay under advisory criteria/less
than 45 mph. 24-hr chances for peak daily gusts (maximum gusts for
the day) exceeding 40 mph on Friday range 50-90% across the
eastern Gorge into the Lower OR Basin and Kittitas valley, highest
odds across the Kittitas Breezeway. Meantime, modest quantity of
moisture accompany the system will promote low-end rain chances
across the crest of the WA Cascades. Otherwise, highs will be
cooler than Thursday, around a few to several degrees below
normal.

.LONG TERM...Friday night through Wednesday...Sensible weather
concerns through the extended forecast will center around the
approach and passage of an upper level low through the
weekend(confidence 70-80%), followed by a general troughing
pattern into the middle of next week(confidence 45-60%). Overall,
conditions will remain dry in the lower elevations with periods of
rain showers impacting mountain zones. There are also concerns
with breezy to windy conditions developing through the weekend.

There remains excellent agreement amongst ensemble and
deterministic model guidance that Friday night will start with an
upper low centered just west of Vancouver Island while a cold
front at the surface is pushing across the PacNW. The center of
the upper low will move inland along the US/Canadian border
through Saturday, then exit into central Canada early Sunday while
leaving the PacNW under an upper trough pattern into the start of
next week. The WA Cascades, and to a lesser extend to the OR
Cascades, will see the best chances of precipitation through early
Sunday morning, with NBM chances of 0.1 inches of QPF in a 48
hour period between 40-70% (best chances near the crest). The
eastern mountains, however, will remain fairly dry, though chances
for only 0.01 inches of QPF are only 20-40%. As the center of the
low moves inland Saturday, the cold core aloft will lead to
increasing chances (only up to 15-20%) for isolated thunderstorms
along the WA Cascades, with best chances staying west of the
Cascades.

Breezy winds between 20-30 mph and gusts around 40 mph developing
early Friday will continue through the evening hours as the cold
front continues to induce a tight cross-Cascade pressure gradient.
The cold front will cross the Cascades and push across the
forecast area Saturday, bringing with it the strongest winds of
the weekend with marginal conditions for wind advisory criteria.
The strongest winds both days will be through the eastern Columbia
Gorge, Simcoe Highlands, Kittitas valley, and the OR Columbia
Basin; probabilities of 24 hour max wind gusts exceeding 45mph in
these areas is between 40-70% Friday and 65-90% Saturday. Winds
will be locally breezy Sunday behind the exit of the upper low
center and the cold front.

Uncertainty in the pattern grows Monday into the middle of next
week as ensemble guidance struggles with what to do with the
lingering trough over the PacNW, and whether or not another trough
approaches the region by Wednesday. About 70% of members made up
from the GFS, ECMWF, and Canadian ensembles favor upper level
troughing slowly moving east, keeping it over the PacNW for a
longer period Monday into Tuesday; meanwhile the remaining
members push the trough east allowing a transient ridge to move
inland. Tuesday into Wednesday, around 55% of ensemble members
favor some form of transient ridging over the region, while the
remaining members favor a trough continuing to sit over the PacNW.
Confidence is moderate (60%) in locally breezy winds and light
precipitation (<0.1 inches of QPF) continuing across the Cascades
and portions of the eastern mountains with either pattern
evolution. However, confidence is low (30-40%) in the temperature
forecast during this period as the ridging pattern would result in
warmer temperatures compared to the troughing pattern. In fact,
this is represented as a range between 7-10 degrees between the
NBM max temperature 25th and 75th percentiles, where in the lower
elevations the 25th percentile is in the mid to upper 70s, and the
75th percentile in the mid to upper 80s. Lawhorn/82

&&

.AVIATION...18Z TAFs...VFR conditions will
prevail through the period. Winds will be light, less than 12kts,
through the period. Except at site DLS where winds will be
12-17kts with gusts up to 25kts through early this evening.
Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  83  52  73 /   0   0   0   0
ALW  49  87  56  76 /   0   0   0   0
PSC  50  87  57  79 /   0   0   0   0
YKM  46  84  49  74 /   0   0   0   0
HRI  49  87  55  78 /   0   0   0   0
ELN  46  81  49  69 /   0   0   0   0
RDM  42  82  42  72 /   0   0   0   0
LGD  45  84  49  72 /   0   0   0   0
GCD  47  89  49  75 /   0   0   0   0
DLS  51  84  52  73 /   0   0   0   0

&&

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

$$

SHORT TERM...80
LONG TERM....82
AVIATION...82