777
FXUS66 KPDT 150850
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
150 AM PDT Sun Sep 15 2024

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

Bottom Line Up Front

1. Rain across central OR and central OR mountains

2. Breezy winds through the Gaps Tuesday

3. At or near normal temperatures

Models are in relatively firm agreement through the short term with
an upper level low making its way down the coast of Canada and into
the forecast area. Models show the low to elongate along the
Cascades and bringing moisture up the leading edge of the low across
central OR through the eastern mountains. Southwesterly flow aloft
will dominate the region bringing with it near normal temperatures.
Models at the surface show the pressure gradients tightening along
the Cascades by as much as 12 mb which will bring breezy conditions
to the Cascade Gaps on Tuesday. As the low tracks to the south
undercutting the region, some wrap around moisture will make it to
the Wallowa Mountains.

The upper level low headed this way will bring increased chances of
rain across portions of the CWA. Rainfall is expected to stretch
across central OR, along the eastern mountains and into Wallowa.
Looking at the raw ensemble rainfall totals, 50-70% of the raw
ensembles show the 48 hour total for central OR to be roughly 0.05
inches of rain. 80-100% of the raw ensembles have 0.15-0.3 inches of
rain along the eastern mountains and 50-70% have 0.10 inches along
the Wallowas. As the low moves off towards the east, models show
some wrap around moisture pushing rainfall into the Wallowa again,
however, rainfall amounts will vary depending the extent of the
track. As of now, NBM show a 50-70% chance of an additional 0.05-
0.01 inches of rain through Wallowa County.

Models at the surface show a tightening of the surface pressure
gradients as the upper level low elongates and moves southward. GFS
and the SREF models both show the cross Cascade pressure gradients
tightening between 9 to 12 mb Tuesday. This will bring breezy
conditions to the Cascade Gaps with 60-80% of the raw ensembles in
agreement that the Gorge, lower Columbia Basin, Kittitas Valley and
the foothills of the Blues will see sustained winds of 35 mph or
greater. 30-60% of the raw ensembles also how the same areas seeing
gusts to 40 mph. After Tuesday, models begin to show the surface
pressure gradients relaxing bringing winds back to normal across
much of the area.

Lastly, with the incoming flux of southerly flow aloft, EFI shows
temperatures through the short term to remain at or near normal. The
NBM shows much of the lower elevations, central OR and
Kittitas/Yakima Valleys to remain in the upper 60s to low 70s with a
few isolated locations in the Basin seeing mid to upper 70s today
with over 60% of raw ensembles agreement. Temperatures will increase
slightly tomorrow with the NBM showing the Basin, adjacent valleys
and the Gorge in the 80s, foothills of the Blues and central OR in
the low to mid 70s and the higher terrains in the upper 50s to low
60s  with roughly 60% of the raw ensembles in agreement.
Temperatures will decrease a few degrees Tuesday. Bennese/90

.LONG TERM...Wednesday through Sunday...Models are in pretty good
agreement through the period with only minor differences in timing
and strength of the broad upper level trough and amplifying ridge
late in the period. Cluster analysis reflects this nicely. However,
two clusters (40%) show a more troughy solution over the weekend.
We`ll have to keep a close watch to see if other clusters begin to
converge on this solution. Ensembles show the main energy over CA
and NV by the start of the period with drier, northerly flow
developing over the region Thursday. The GFS ensemble shows a
stronger ridge developing over the eastern Pacific continuing
northerly flow over the area while the ECMWF ensemble is a little
less amplified resulting in the flow becoming northwest. They come
back into agreement Friday with both showing northwest flow aloft as
the upper trough moves east and a long stretch of zonal flow
develops over the eastern Pacific. The Northwest flow continues into
the weekend as a ridge develops over the eastern Pacific. This
pattern is generally a dry one, but favored northwest-north facing
slopes could see an isolated shower.

There`s a low-moderate chance (20-35%) of receiving 0.10 inch of
rain Wednesday over our southern CWA, mainly Oregon, but
probabilities drop to less than 10 percent for the reminder of the
period as drier, northwest-northerly flow filters into the area.

There`s a low chance (10-15%) of breezy conditions developing
through the Columbia River Gorge and Cascade gaps Thursday and
Friday.

Daytime highs are expected to remain near to slightly below normal
through the period. Earle/81


&&

.AVIATION...Previous discussion...06Z TAFs...VFR conditions with
winds 10 kts or less are expected through the TAF period.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  66  48  71  50 /  30  30  20  10
ALW  69  50  74  55 /  40  30  20  20
PSC  73  55  79  56 /  10  10  10  10
YKM  74  47  81  47 /  10  10   0   0
HRI  71  52  79  55 /  10  10  10  10
ELN  73  49  80  50 /  10   0   0   0
RDM  65  43  69  42 /  10  10  20   0
LGD  64  48  69  49 /  50  40  30  30
GCD  63  47  69  44 /  60  40  30  20
DLS  75  54  82  55 /   0  10   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....81
AVIATION...77