829
FXUS66 KPDT 222307
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
407 PM PDT Sun Sep 22 2024

Updated Aviation Discussion

.SHORT TERM...Today through Tuesday...

Bottom Line Up Front

1. Breezy conditions through Cascade Gaps today

2. Dry and warming conditions through mid-week

Models show the flattened ridge to be steadily creeping overhead
while an upper level shortwave makes its way across the area.
Current observations show the shortwave to be just west of the
Cascades over the Olympic Peninsula making its way eastward. As the
shortwave traverses over the Cascades a bit later today, models show
an increase in the surface pressure gradients at the surface,
especially between Seattle and Ellensburg. Roughly 4 mb increasing to
7 mb during the passage will increase winds through the Kittitas
Valley as well as the Gorge with the energy of the wave focused
closer to the Kittitas Valley. 80-100% of the raw ensembles show the
Kittitas Valley will see sustained winds of 20 mph or greater with
gusts gusts to 30 mph beginning around 3 PM and lasting through the
overnight period and shifting slightly eastwards from Ellensburg.
The Gorge however, only show 40-60% of the raw ensembles seeing 20
mph sustained winds with less than 15% showing gusts to 30 mph and
tapering off around 10 PM. With that said, the Kittitas Valley will
continue seeing breezy conditions through the period as the ridge
remains more zonal bringing continued westerly flow aloft keeping
the winds elevated near 20 mph with 60-80% of the ensembles in
agreement.

After today, the most exciting thing is...well...nothing in the
short term. Benign weather will persist through Tuesday as the
ridge settles in overhead. Models show the ridge to be flat with the
majority of the amplitude directed over central OR. Temperatures are
steadily increasing as the ridge remains in place with the warmest
temperatures settling over central OR Tuesday. Over 60% of the raw
ensembles have the majority of the low elevations and central OR in
the low 80s, 70s along the mid elevations and 60s along the higher.
Mondays temperatures creep up a few degrees and then settle into the
warmest temperatures on Tuesday. EFI shows Tuesday to also be above
seasonal average with temperatures pushing into the 90s through
central OR with 70% of the raw ensembles in agreement. As for the
lower elevations 60% of the ensembles show the PDT area in the low
mid to upper 80s and 80% show the same temperature as PDT in the
Basin. Mid level and higher terrains will see low to mid 70s. Not so
fall after all this week...yet. Bennese/90

.LONG TERM...Wednesday through Sunday...A fairly strong cold
front has been progged by the models for at least several days
now, so confidence is high that this front will have some impacts
on the weather. Main impact will be winds. The ETA of the front
will be late in the afternoon to early evening, and winds aloft
will increase and pressure gradients will tighten with the cold
frontal passage. Ensemble means show 25-30 kts at 850 mb and 40-45
kts at 700mb over the Lower Columbia Basin. The ECMWF EFI places
central Oregon in the higher category of above average wind gusts
with a 0.85 out of 1.0. I am not anticipating a high wind event,
but there may be a need for wind advisories in some zones. There
is deep dry air behind the front, but the dry air intrusion will
occur as winds decrease. The afternoon RHs will be in the 20s to
lower 30s--not critical for red flag conditions (confidence 60%).
Most precipitation on Wednesday will be west of the Cascades, but
there will be enough orographic lift for showers east of the
Cascade crest and the northern Blue Mtns.

There will be a cooling trend behind the front starting Thursday.
Models are in agreement of a straight zonal flow through Friday for
dry and seasonal weather.  However, model differences begin to show
for the weekend forecast.  There is a shortwave advertised by the
models north of the CWA, but there are timing differences as well as
minor differences in the amplitude of the trough.  Some show the
trough passage along the BC/WA border on Saturday (mainly the ECMWF
ensembles) while others have a little more amplitude and slower
timing (mainly the Canadian) and track it across WA state. Current
forecast will keep mostly dry conditions this weekend, but a slight
chance of showers may need to be introduced if models come into
better agreement with the timing and strength of the trough.
Wister/85

.AVIATION...00Z TAFs...VFR conditions to prevail through the
period. High level clouds sct-bkn 15kft-25kft will continue to
impact sites through the period. Site DLS will see winds 12-17kts
with gusts up to 25kts through this evening. Otherwise, winds will
be light, less than 12kts, through the period at all sites.
Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  51  79  53  87 /   0   0   0   0
ALW  55  82  56  89 /   0   0   0   0
PSC  56  83  56  87 /   0   0   0   0
YKM  52  84  53  87 /  10  10   0   0
HRI  55  83  55  89 /   0   0   0   0
ELN  56  82  54  87 /  10  10   0   0
RDM  46  80  48  90 /   0   0   0   0
LGD  48  78  49  86 /   0   0   0   0
GCD  46  78  50  87 /   0   0   0   0
DLS  59  86  59  92 /  10  10   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....85
AVIATION...82