975
FXUS66 KPDT 071118
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
318 AM PST Thu Nov 7 2024

Updated Aviation Discussion

.SHORT TERM...Today through Saturday...Ridging continues to
prevail over the forecast area, leaving us with dry and clear
weather through at least Saturday morning. High pressure may
induce areas of patchy fog along river valleys, as it did around
the Tri-Cities early Wednesday morning, however confidence is
still on the lower end (<30%) in any substantial, area-wide fog
developing, even as high pressure persists, as the airmass
overhead is pretty cold and dry. Still, did put some mention of
fog in and around the lower Basin of Washington for Thursday and
Friday morning, given what occurred yesterday morning in the Tri-
Cities.

Heading into the weekend, a shortwave will move into the PacNW,
bringing in a round of precipitation across the forecast area. High
pressure and oncoming SW flow ahead of this wave will make for
elevated snow levels (generally above 6000-7000 ft), so expecting
mostly rain outside of high mountain peaks. Models seem to
consistently delay the onset of this shortwave, so did opt for a
mostly dry forecast through Saturday, with precip arriving Saturday
evening for the entire area. This looks to be a quick hitting system
with relatively light precip, but will mark a return to more active
conditions heading into next week. Evans/74

.LONG TERM...Sunday through Thursday...Unsettled weather
conditions will be in store for the region as a series of upper
level troughs bring persistent chances of rain and mountain snow
through the middle of next week.

Sunday starts with a shortwave trough passage that`ll continue to
bring light precipitation chances across the mountain areas
through the afternoon. Snow levels will be around 5.5kft across
the northern tip of the forecast area, with snow levels rising
up to 6.5kft to 7kft across the southern half of the forecast
area. By Sunday evening, ensemble guidance shows an upper trough
with a leading surface cold front arriving to the PacNW. The
coupled system will bring another round of precipitation area-
wide, with the best chances associated with the cold front
passage Monday morning/afternoon in the lower elevations. Snow
levels will start off above 5kft Monday morning, but a colder
airmass filtering in behind the cold front passage will lead to
snow levels dropping to around 4kft Monday night. This will result
in a transition from rain or rain/snow mix to snow across many
mountain locations throughout Monday. By Monday night, NBM 24-hr
probabilities of snow accumulations greater than 3 inches shows a
65-75% chance along the northern Blues and peaks of the southern
Blues, as well as a 75-90% chance along the OR Cascade crest and
along ridges above pass level along the upper east slopes of the
WA Cascades. The frontal passage Monday into Tuesday morning will
also produce breezy to locally windy conditions across the lower
elevations. That said, NBM guidance only shows a 50-70% chance of
exceeding 40mph wind gusts Monday and Tuesday morning in wind
prone areas (i.e. Columbia Basin, Cascade gaps, Simcoe
Highlands).

Tuesday, the upper trough will exit the forecast area allowing a
transient ridge to push into the PacNW into Wednesday morning,
though ensemble cluster guidance is in disagreement on if the
trough exits Tuesday morning or later in the afternoon. That said,
confidence remains moderate (50-60%) in light precipitation
chances continuing in the mountains through early Wednesday
morning. A majority of cluster solutions (>70%) show the ridge
axis pushing east of the region by Wednesday afternoon, with the
arrival of another upper trough and surface frontal system behind
the upper ridge exit. The current cluster ensemble solutions all
favor another round of precipitation chances area-wide, however,
disagreements amongst the strength of the incoming front/upper
trough has resulted in some solutions (30% of members) favoring
higher snow levels Wednesday into Thursday, while the remaining
members favor lower snow levels but with differing precipitation
amounts. As a result, confidence in going snow amount forecast is
low (20-30%). Lawhorn/82

.AVIATION...12Z TAFs...VFR conditions to prevail at all sites.
CIGS will remain mostly clear, though can`t rule out passing few-
sct high level cloud cover later in the evening. Winds will be
light, less than 12kts, at all sites. Lawhorn/82


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  52  29  52  31 /   0   0   0   0
ALW  52  30  53  33 /   0   0   0   0
PSC  51  32  51  34 /   0   0   0   0
YKM  53  28  53  31 /   0   0   0   0
HRI  53  31  52  33 /   0   0   0   0
ELN  53  30  53  33 /   0   0   0  10
RDM  60  28  62  33 /   0   0   0   0
LGD  52  29  55  33 /   0   0   0   0
GCD  56  30  61  32 /   0   0   0   0
DLS  57  33  56  38 /   0   0   0   0

&&

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

$$

SHORT TERM...74
LONG TERM....82
AVIATION...82