567
FXUS66 KPDT 081723
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
923 AM PST Fri Nov 8 2024

Updated aviation discussion

.SHORT TERM...Today through Sunday...Very little to note on
satellite and radar imagery tonight as an upper level ridge over
the PacNW provides dry and calm conditions.

The upper ridge will slowly push east today, allowing a shortwave
trough to arrive to the PacNW by tomorrow morning and pass over
the region through Sunday morning. Surface pressure gradients will
tighten across the Blues later this evening ahead of the shortwave
trough arrival, resulting in breezy winds (gusts 25-35mph)
developing in the southern Grande Ronde valley tonight. Snow
levels will remain fairly high between 5.5kft to 7kft with the
passage of this system, resulting mostly in snow along the higher
peaks of mountain areas. This will result in mostly rain and a
rain/snow mix across many mountain locations tomorrow, with a
probability of 50-60% of at least 0.1 inches of QPF along the
northern Blues and OR Cascade crest; probability of 0.25 inches
along the WA Cascade crest is 65-80%. While light rain showers
will develop over the lower elevations, probabilities for any
measurable rainfall through Saturday night in central OR and the
Columbia Basin and adjacent valleys is only 40-55%, while foothill
locations are 55-70%.

A brief period of dry conditions will develop the first half of
Sunday as a transient ridge quickly moves across the PacNW. Behind
it, an approaching upper trough with a frontal system will push a
weak warm front across the PacNW, resulting in precipitation
chances increasing across the Cascade crest by the mid to late
afternoon. The warm sector will lift across the forecast area
Sunday evening and overnight, increasing chances of rain and high
mountain snow east of the Cascades. By the end of Sunday night,
the Cascade crest will see a 70-90% chance of 0.5 inches of QPF,
with the best chances along central WA Cascade crest; snow levels
will generally remain above 6kft in the mountains, with a less
than 25% chance of measurable snowfall at the pass levels. In the
northern Blues, chances of only 0.25 inches of QPF are between
40-50%, with precipitation occurring mostly as rain through
Sunday. Pressure gradients across the eastern mountains will
tighten ahead of the trough and cold front arrival to the
intermountain PacNW, resulting in breezy south to southeast winds
(gusts 15-25mph) developing through the southern Grande Ronde
valley, central OR, and the Blue Mountain foothills Sunday night.
Lawhorn/82


.LONG TERM...Monday through Friday...The long term remains
progressive in nature as passing systems should keep us active in
regards to precipitation and winds, but the positioning of these
systems will bring temperatures up several degrees and sustain a
period of warmer than average highs and lows until then end of the
forecast period when deep troughing should finally bring us back
to near normal temperatures in the region.

The long term begins with a deep upper low off of the Canadian
coastline bringing a trough and occluding frontal boundary across
the region. As this system passes us by, flow will become
generally zonal on Tuesday under weak transient ridging, but by
Thursday we`ll be back to southwesterly flow aloft as another deep
upper low approaches and moves into the region by Friday, with
much deeper troughing over the entire West Coast expected that
will then place us under northerly to northwesterly flow aloft to
end the period. Under this pattern, primary sensible weather
concerns lie in mountain snow and surface winds. Daily snow totals
in the mountains of several inches are expected, lying between
elevations of 4-6+ thousand feet, lowering or increasing between
periods of cooler and warmer temperatures aloft with the passing
systems. These may be low enough in elevation and enough total
accumulation to promote some highlights, but these will likely be
advisory level at best if they do occur. The lower elevations
won`t fully miss out, though this will mostly be relegated to
rainfall, with QPF totals across our population centers through
the entire period between 0.3-1.5 inches, highest in the Columbia
Gorge as well as our mid-elevation locations. But these QPF
totals will be over the full 5 day period, with only light to
occasionally moderate rainfall expected day to day. Finally, these
ebbing pressure gradients should help produce breeziness in the
winds, generally impacting our windier locations such as through
the Cascade gaps and into the Columbia Basin, but overall model
ensembles do not highlight significant concerns for stronger
gusts.

There is moderate confidence (50-60%) in the long term forecast,
hindered by discrepancies in the overall features evolving across
our region. Ensembles all highlight these features as being
expected, but differentiate between the strength and depth of
them. This notably comes into play with the end-week system, as
23% of members move this system inland faster and a bit weaker
overall, and 6% of members have completely jumped the shark and
show no troughing at all. Both of these solutions are outliers
though, and the major clusters indicate a deep trough encompassing
the west coast on Friday. Expect a wet and (seasonably) mild to
warm week as highs in our population centers range in the 50`s
with overnight lows in the mid 30`s to mid 40`s, finally dropping
to more seasonably normal temperatures by Friday (40`s to 40`s for
highs and near to below freezing lows). Goatley/87


&&

.AVIATION...18Z TAFs...VFR conditions expected over the next 24
hours with some SCT-BKN200-250 lowering to 150-200 Saturday. Some
fog may be possible near PSC overnight through Saturday morning.
Winds 10 knots or less all sites.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  52  33  54  39 /   0   0   0  30
ALW  52  35  55  42 /   0   0   0  40
PSC  50  36  53  40 /   0   0   0  20
YKM  53  33  52  33 /   0   0  10  20
HRI  52  35  54  41 /   0   0   0  20
ELN  52  33  52  33 /   0   0  10  30
RDM  62  34  57  35 /   0   0   0  20
LGD  54  35  53  39 /   0   0   0  40
GCD  61  34  59  38 /   0   0   0  30
DLS  56  38  58  43 /   0   0  10  30

&&

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

$$

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