262
FXUS66 KPDT 261122
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
422 AM PDT Wed Jun 26 2024

Updated Aviation Discussion

.SHORT TERM...Today through Friday...A passing shortwave trough
and cold front along with pockets of favorable instability should
allow for areas of showers and some thunderstorms today, with the
low associated with this trough then progressing across the PacNW
on Thursday, followed by a transient ridge on Friday bringing at
least a day of quieter weather across the area.

For today, a few showers are already noted moving into the Central
Oregon area. Look for activity to see an uptick across both the
Cascades and adjacent valleys and eastern slopes, along with the
eastern mountains of Oregon and Washington. Activity may even
slip into the lower Columbia Basin of Washington at times later
this morning, providing a brief shower just west and northwest of
the Tri-Cities. The eastern mountains should have pockets of
favorable instability for thunderstorm development by this
afternoon (around 200-600 J/kg), but overall parameters are
unlikely to be supportive of anything noteworthy outside a few
lightning strikes and perhaps locally breezy, shifting winds.

On the note of winds, a breezy day is in store across the region,
but currently anticipate activity should be below highlight level.
The NBM shows a broad swath of 40-80% probability of gusts
reaching 45+ mph in the Oregon Columbia Basin and into the
Foothills of the Blues, with a much higher 50-90% chance in the
higher terrain of the Simcoe Highlands as well as a few portions
of the higher terrain near the Kittitas Valley. Not seeing enough
mixing from the mid levels however, even though pressure gradients
are conducive of near advisory level winds, and expectation is
that we`ll see an isolated gust or two reaching advisory level of
45+ but not widespread enough to warrant the advisory itself.
Breezy again tomorrow as well, though lower with a more limited
chance of 45+ gusts from the NBM (30-60% probability) once again
for aforementioned areas from above. Widespread gusts otherwise
today and tomorrow around the 20-30 mph range.

Meanwhile overnight tonight into Thursday, mountain precipitation
becomes the dominant activity, mostly along the Cascades as rain
shadowing takes over from westerly flow. A few showers may be
possible tomorrow morning into the eastern mountains of OR/WA as
well, but with PWAT values dropping to around a half inch or less,
unlikely to see any exciting rainfall amounts and limited to a
tenth of an inch or less in most spots. By Friday our weather
tempers down as a transient ridge keeps winds calm and
precipitation nil. Finally, temperatures will see a bit of a
rollercoaster, with widespread highs for our population centers in
the 80`s to low 90`s today, followed by a significant drop into
the 70`s and very low 80`s tomorrow behind the cold front,
rebounding with the ridge on Friday into the widespread 80`s
(confidence high all days, 70-90%). Goatley/87

.LONG TERM...Saturday through Wednesday...Main concerns through
the long term forecast will center around a trough passage over
the weekend into early next week, with otherwise low concerns the
rest of the period.

Saturday starts with the PacNW between two synoptic features,
upper level trough centered just offshore, and an upper ridge
centered along the norther Rockies. Deterministic and ensemble
guidance are in good agreement that the forecast area will remain
under the influence of the ridge through the afternoon Saturday,
resulting in the warmest day in the extended forecast, with low
mid 80s to low 90s across the forecast area (confidence 60-70%).
While the first half of Saturday will remain dry, a shortwave
impulse rounding the upper trough will result in scattered shower
chances developing across the Cascade crest and eastern mountains
beginning in the evening. The upper trough will then move across
the PacNW Sunday through early Monday, reinforcing chances of
showers across the Cascade crest and the eastern mountains. Rain
accumulations will be fairly light with these shower chances, with
the NBM only showing chances of 35-50% for 0.05 inches of rain
through Sunday night along the Cascade crest and eastern
mountains. That said, a few showers across the higher terrain in
the Blues and Wallowas could tap into increasing surface
instability (50-65% chance of 150 J/kg CAPE) Sunday afternoon,
resulting in isolated thunderstorms capable of gusty winds, small
hail, and downpours. Besides precipitation, or lack there of,
ensemble guidance points to the development of widespread breezy
to locally windy conditions Sunday as the trough moves overhead,
as well as Monday as the influences of the trough passage linger
throughout the day. For the usually windy locations (i.e. OR
Columbia Basin, eastern Gorge, Simcoe Highlands, WA Cascade east
slopes, and Kittitas valley) the NBM is showing the probability of
peak wind gusts reaching 45mph or greater between 65-85% Sunday,
and 50-80% Monday.

Late Monday through Wednesday, differences in ensemble mean
guidance begin to present itself. While both GFS and ECMWF
ensemble guidance place the region under a northwest flow aloft
initially, the GFS members favor a broad shallow trough over the
PacNW, whereas the ECMWF members favor a zonal flow over the
region. In either solution, conditions will remain relatively dry
with very little precipitation chances, as well as breezy
conditions through the Cascade gap areas through the midweek
(confidence 60%). Instead, the impacts will be to temperatures,
where the GFS solutions favor temperatures about 5 degrees cooler
than the ECMWF solutions. These differences would result in
temperatures each afternoon firmly in the 80s across the lower
elevations, or mid 70s to lower 80s with the cooler solutions.
Lawhorn/82

.AVIATION...12Z TAFs...VFR conditions to prevail through the
period. Increasing mid to upper level cloud decks of sct-bkn will
impact sites through the period. Incoming system will provide
enough moisture for shower and isolated thunderstorm chances
through the afternoon, especially over mountain areas. Vicinity
showers were included for sites DLS/PDT/ALW/PSC, while site YKM
will see the best chance of rain showers this morning into the
early afternoon. Winds will increase to 12-20kts with gusts up to
30kts possible this afternoon, with 12-15kt winds prevailing
overnight at sites DLS/PDT/ALW/PSC. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  85  52  74  49 /  10  10  10   0
ALW  91  56  78  53 /  20  10  10   0
PSC  93  58  80  54 /  10   0   0   0
YKM  87  51  77  48 /  40  10   0   0
HRI  90  57  79  52 /  10   0   0   0
ELN  81  52  71  51 /  50  10  10   0
RDM  81  45  72  42 /   0   0   0   0
LGD  86  50  69  46 /  20  10  10   0
GCD  90  50  73  45 /  20   0   0   0
DLS  79  57  74  53 /  20  10   0   0

&&

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

$$

SHORT TERM...87
LONG TERM....82
AVIATION...82