341
FXUS66 KPDT 300950
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
250 AM PDT Sun Jun 30 2024

.SHORT TERM...Today through Tuesday...Current nighttime satellite
imagery and radar returns show a narrow band of showers exiting
into ID, with scattered cloud cover developing behind this band.
Breezy winds also developed late yesterday afternoon with the
shortwave passage, and have persisted slightly through the
Kittitas valley tonight.

The band of showers across far eastern WA/OR will exit into ID
ahead of an upper trough passage across the region today. An upper
trough and surface cold front passage today will continue to
bring isolated/scattered showers across the WA Cascade crest as
well as Wallowa county through the afternoon. Weak instability and
modest low level lapse rates will also allow for slight chances
(15-25%) of isolated thunderstorms across eastern Wallowa county
this afternoon. Breezy wind will also develop through the Cascade
gaps and into the Columbia Basin, with generally 15-25mph
sustained winds and gusts up to 40mph. A localized gust up to
45mph may be possible through the Simcoe Highlands and portions of
the Kittitas valley, with NBM probabilities of 55-75% through
today. A marine push associated with the incoming trough/frontal
passage will keep RHs above critical levels, though the
anticipated breezy conditions will continue to bring elevated fire
weather concerns.

A secondary shortwave behind the upper trough axis exit will
support breezy winds through the lower elevations Monday, with
another day of 15-25mph sustained winds and gusts up to 40mph.
That said, probabilities of 45mph or greater gusts through Monday
will increase to 70-85% through the Kittitas valley, Simcoe
Highlands, eastern Gorge, and the Columbia Basin. While fire
weather concerns will continue to be elevated through Monday, RHs
are anticipated to remain above critical thresholds in the
afternoon (confidence 70-80%). Upper level ridging will amplify
across the eastern Pacific Tuesday, resulting in a dry northwest
flow aloft over the PacNW. Breezy winds will continue through the
Cascade gaps, with light to locally breezy winds elsewhere.
Lawhorn/82

.LONG TERM...Wednesday through Sunday...Warm to hot temperatures and
little to no precipitation is forecast as an upper-level ridge
dominates the region`s weather (95% chance through Saturday, and 75%
chance Sunday). The main weather concern will be increasingly hot
temperatures and Moderate to locally High HeatRisk for the lower
elevations Friday through Sunday.

On Wednesday, the 500-mb pattern will be characterized by downstream
troughing over the Northern Plains and Northern Rockies, with an
anomalously strong upper-level ridge in place upstream in the
Pacific Ocean. This will place the forecast area under a dry
northwest flow aloft. Deterministic guidance still advertises a
shortwave sliding southeast across eastern WA and northeast OR
during the day, but the dry air mass should preclude any significant
chances of precipitation (<5% area-wide) as the shortwave traverses
the region. Breezy to locally windy gap winds are likely (>90%
chance) through the Kittitas Valley and eastern Columbia River
Gorge. Currently, no Red Flag conditions are forecast, and NBM 24-hr
probabilities of advisory-level wind gusts are 30-70% through the
Kittitas Valley so wind highlights are not anticipated at this time.

For the 4th of July, over 80% of ensemble members keep the offshore
ridge in place. The remainder advertise a more progressive longwave
pattern with the ridge axis shifting inland. The latter solution
would result in the warmest temperatures east of the Cascades,
though the difference would only be several degrees relative to the
favored solution. Afternoon high temperatures are currently forecast
to be 5-10 degrees above normal, resulting in some areas of Moderate
HeatRisk for the lower elevations on the 4th of July.

Friday and Saturday, ensemble clusters reveal a broader range in
member solutions, though the main differences are in how members
handle an upstream closed low/open wave and exactly where the axis
of the ridge will be placed. Per 00Z ensembles, the upper ridge axis
will likely (78% of members) remain offshore, though 17% of members
place the ridge overhead, and a minority of members (4%) break the
ridge down altogether and bring a trough into the PacNW. The latter
solution would result in cooler temperatures, while the overhead
ridge would result in the warmest weather.

Sunday, guidance shows the most uncertainty in the longwave pattern.
The multi-model ensemble mean places the upper-level ridge axis
overhead, though individual clusters range from an anomalously
strong ridge overhead (18%) to a trough passing to the north
resulting in a suppressed ridge (27%) to an offshore ridge (55%).

Regarding uncertainty Friday through Sunday, ~50% of ensemble
variance is due to differences in the location of the upper ridge,
while an additional ~25% is associated with the magnitude of the 500-
mb height field over the PacNW.

Despite persistent low afternoon relative humidity (upper single
digits to upper teens for the lower elevations), Red Flag conditions
are not anticipated to be widespread enough to warrant highlights.
However, fire weather concerns will still be elevated.

Precipitation chances are extremely low (<5% chance) through the
period. Plunkett/86


&&

.AVIATION...Previous Discussion...06Z...VFR conditions will
prevail through the period with the primary focus being the winds.
All TAF sites will see breezy conditions with TAF sites
RDM/BDN/YKM all seeing sustained winds between 10-20 with gusts to
30 mph. PDT/DLS will see sustained winds of 13 to 20 kts and 10
to 30 kt gusts respectively. Mostly high clouds above 10kft with
PDT and ALW seeing trace amounts of precipitation between 06Z and
08Z.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  55  82  53 /   0   0   0   0
ALW  86  58  85  57 /  10  10   0   0
PSC  89  60  88  58 /  10   0   0   0
YKM  86  55  85  53 /   0   0   0   0
HRI  88  59  87  56 /   0   0   0   0
ELN  78  55  78  53 /  10   0   0   0
RDM  80  49  79  45 /   0   0   0   0
LGD  79  50  78  49 /  10  10  10   0
GCD  81  50  80  47 /   0   0   0   0
DLS  84  60  83  56 /   0   0   0   0

&&

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

$$

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