000
FXUS66 KPDT 082157
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
156 PM PST Fri Dec 8 2023

.SHORT TERM...Tonight through Sunday...A transiting ridge of high
pressure is moving into the region from the west this afternoon
bringing an end to todays mountain showers. However, the next system
is approaching and will begin to increase clouds overnight ahead of
a warm front moving into the region Saturday reaching the Cascades
late morning to early afternoon. Precipitation will begin as snow in
the Cascades and a rain snow mix in the lower elevations along the
east slopes of the Cascades and rain in the Lower Columbia Basin.
This will spread east into the eastern mountains by late Saturday
afternoon and evening as snow. Snow levels begin to increase west to
east across the forecast area Saturday night changing snow over to
rain. The higher snow levels begin reaching the eastern mountains
late Saturday night and early Sunday. There are some concerns for
freezing rain during this transition period along the east slopes of
the Washington Cascades and the eastern mountain valleys with
confidence being low to moderate. Snow levels by Sunday will be 5000
to 7000 feet. The moist westerly flow continue through Sunday night
with a slight drop in snow levels but still generally remaining
above pass levels. A Winter Weather Advisory has been issued for the
Upper Slopes of the Eastern Washington Cascades Crest for snow and
mixed precipitation. Other advisories may eventually be needed but.

.LONG TERM...Monday through Friday...Much of next work week looks to
be quiet as ridging dominates the region and makes for dry weather,
primarily for Tuesday and Wednesday. Cold pooling may impact the
Basin for the first half of the period, potentially leading to
valley fog that has the potential to last well into the day,
particularly in the lower Basin. Confidence in details is on the
lower end, however, as some ensemble guidance, namely the NBM, has
been in conflict with what the deterministic models are generally
depicting as far as the synoptic pattern is concerned.

Monday starts off with a departing cold front associated with a
developing trough that will dig into the intermountain west.
Ensemble clustering is generally in good agreement on this, which
will lead to light precip across the area Monday with snow levels in
the 4000-5000 ft range. Cold air advection will then follow, leading
to cold pooling in the Basin. These conditions are typically ripe
for fog development, but held off any mention in the grids as
northerly flow ahead of Monday`s system may produce some high clouds
that inhibit fog from forming. That, and the NBM seems to be
particularly aggressive about PoPs in the midweek despite
deterministic guidance and ensemble clustering suggesting a dry
pattern Tuesday and Wednesday. Scaled back PoPs across the CWA from
what the NBM had for these days, but will hold off on fog mention
until guidance comes into better agreement.

Temps will slowly tick downward through the week before ensemble
clusters hint at the arrival of a SW wave early Thursday. Models are
sparse on QPF/PoPs, as to be expected this far out, but Thursday
looks to be the next best chance for precip after Monday. Friday
onward, ensembles once again introduce ridging into the forecast
area. Evans/74

&&

.AVIATION...00z TAFs...VFR conditions are expected for most of the
period. The trend for this evening will be clearing skies for all
TAF sites, with light, terrain-driven winds overnight. Starting late
Saturday afternoon, a weather system will arrive and bring precip to
all TAF sites. Most sites should see rain, possibly light snow in
BDN/RDM, however fzra cannot be ruled out for YKM. Any deterioration
in category associated with tomorrow`s system is expected to be in
the form of low cigs rather than vsby. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  29  44  36  46 /   0  30  90  80
ALW  31  43  36  45 /   0  30  90  90
PSC  32  41  36  44 /   0  40  80  60
YKM  28  35  29  41 /   0  80  80  40
HRI  30  42  35  46 /   0  40  80  70
ELN  26  33  28  37 /   0  80  90  40
RDM  22  41  35  47 /   0  30  40  60
LGD  25  38  31  40 /   0  20  90  90
GCD  22  42  31  46 /  10  20  70  80
DLS  33  41  36  48 /   0  80  90  80

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Winter Weather Advisory from 10 AM Saturday to 10 AM PST Sunday
     for WAZ522.

&&

$$

SHORT TERM...91
LONG TERM....74
AVIATION...74

NWS PDT Office Area Forecast Discussion