Pasco, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

595
FXUS66 KPDT 031148
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
347 AM PST Tue Dec 3 2024

.Updated Aviation Discussion.


.SHORT TERM...Today through Thursday night...Models and ensemble
clusters are in excellent agreement on the evolution of the 500
mb pattern during the short term period. An upper level ridge will
remain over the region through Wednesday. This provides high
confidence (80-90%) that the extensive stratus layer will remain
in place the next couple of days...though the southern edge will
likely oscillate north and south. This will have the biggest
impact on the Bend/Redmond population centers with periods of
freezing fog. High and low temperatures will be modulated by the
extent/persistence of the fog/stratus. Most of the current
fog/freezing fog concerns are where the stratus layer is
intersecting the terrain at elevations of 2000-3500 feet MSL. The
current freezing fog advisories remain in effect and a special
weather statement was also issued for interstate-84 east of
Pendleton for dense freezing fog and slick roads.

For this forecast ended fog after 18Z Wednesday though this may
be a bit optimistic. Wednesday afternoon the ridge begins to shift
eastward as a shortwave trough approaches the area which may help
break up the fog. This feature will only briefly flatten the 500
mb flow and perhaps bring a chance of mainly rain showers to the
Cascade crest Thursday and Thursday night. The NBM currently has
15-30% POPS for this area with the clusters only showing .01-.03
inches of QPF. With such a weak system anticipated and a ridge
forecast to rebuild right behind it, there is a decent chance
(40-50%) that the low stratus does not get scoured out completely
or at least remains in Washington through Thursday and then
expands into northern Oregon Thursday night. This scenario will
have to be evaluated in future forecasts. 78


.LONG TERM...Friday through Tuesday...

Key Messages:

1. Widespread rain chances and mountain snow Saturday into Sunday.

2. Breezy winds Saturday evening through Sunday morning.

3. Near to above normal temperatures through period.

Ensemble and deterministic guidance is in good agreement with the
overall synoptic pattern of an upper level trough approaching the
coast and passing through the Pacific Northwest Saturday into Sunday
morning. This system will bring a more active pattern to the region,
allowing for widespread rainfall, mountain snowfall, breezy winds,
and warm temperatures over the weekend. A warm front will pass over
the area ahead of the upper level system on Friday, attributing to
snow levels rising to 8000-9000 feet as rain chances (50-70%) stay
confined along the Washington Cascades. The upper level trough and
attendant cold front will then approach the Washington coast on
Saturday, pushing across the area as the trough begins to broaden
and dig into northern Nevada by Sunday evening. The cold front will
lead to snow levels dropping to 3000-4000 feet by Sunday morning.
Thus, mountain rainfall will transition to snow Saturday evening as
1-3 inches of snowfall is anticipated to fall along the Cascade
passes through Sunday afternoon. Confidence in these snow amounts
are moderate to high (60-80%) as the NBM suggests a 45-55% chance of
1 inch of snow across Santiam and Snoqualmie Passes between 4 PM
Saturday and 4 PM Sunday. Higher elevations of the Cascades and
northern Blue Mountains are expected to pick up 2-5 inches of
snowfall above 4000 feet. Widespread rain chances (25-65%) will
materialize through Saturday morning, with lower chances (25-35%)
expected across Central Oregon. Saturday does look to be the wettest
day in the forecast, with 0.30-0.60" of rainfall anticipated along
the Cascade and northern Blue Mountains, 0.03-0.15" along the Blue
Mountain foothills and the John Day-Ochoco Highlands, and 0.02" or
less over the Lower Columbia Basin. Areas of Central Oregon,
especially the Bend/Redmond area, will likely stay dry over the
weekend. Confidence in these rain amounts is moderate (60-70%) as
the NBM advertises a 45-75% chance of 0.40" of rainfall over the
Cascades and northern Blues, a 40-60% chance of 0.10" of rainfall
along the northern Blue Mountain foothills, and a 50-70% chance of
measurable rainfall (0.01" or more) across the Lower Columbia
Basin. The surface cold front will continue to exit to our southeast
into Sunday morning as the upper level system encroaches into
northern Nevada and California. Surface high pressure will slide
onshore an into Central Oregon behind the cold front, which will
keep precipitation chances (20-50%) along the Cascades, east slopes,
John Day-Ochoco Basin/Highlands, and the Blue Mountains and
foothills. Rain accumulations will stay confined at elevation across
our mountain zones, with 0.05-0.25" of rainfall likely on Sunday.

The passing cold front on Saturday will set up a pressure gradient
across the Columbia Basin (KPDX-KGEG) of 5-5.5mb as advertised by
the GFS. This will lead to elevated winds across the Basin, with the
highest winds expected along the east slopes of the Washington
Cascades, Simcoe Highlands, Blue Mountain foothills, and the
northern Blue Mountains, peaking late Saturday night into the early
morning hours on Sunday. This cross-basin gradient of 5-5.5 mb is
much less than the normal advisory threshold of 11 mb, but will
still lead to sustained west winds of 15-20 mph with gusts of up to
30 mph. Winds will increase through Saturday afternoon and evening,
peaking overnight before slowly subsiding through Sunday afternoon.

Upper level flow will stay consistently out of the west-southwest
through the weekend, which will lead to warmer air advecting into
the area. This will allow for near to above normal high temperatures
to return to the area Friday through Sunday. As the upper level
trough digs into Nevada and California, flow aloft turns more from
the north to allow a cooling trend to commence as cooler, Canadian
air brings high temperatures back to near normal by Tuesday.
Overnight cloud cover associated with the upper level system will
help to keep low temperatures near to slightly above normal, with
the warmest morning in the forecast occurring on Sunday.

Ensemble clusters are in fairly good agreement, but there are minor
differences in relation to the strength of the upper level ridge
early in the period on Friday. This ridge is what breaks down over
the weekend as the upper level trough passes through the area. 57%
of ensemble members hint at a stronger ridge on Saturday, which
would cause slightly drier conditions along the east slopes and
Basin. Upper level ridging slides into the area Monday, in the wake
of the dropping and departing weekend system. This will help to
bring drier conditions, calmer winds, and cooler temperatures to the
area early next week. 75

&&

.AVIATION...12z TAFs...The status quo from the last couple of days
continues on as ridging sits over our area and the low stratus deck
continues to linger.  BDN has seen FZFG enter the area briefly
bringing conditions to LIFR before finally settling back to VFR,
which we will expect to continue so for the rest of the period.
However the rest of the terminals will continue to experience lower
ceilings and visibilities going into the period. DLS, YKM, and ALW
will experience reduced ceilings, but will be remain in MVFR through
the period. There is a moderate chance (50-60%) that ALW will
degrade to LIFR due to reduced ceilings of OVC004 this afternoon,
which is expected to extend through the remainder of the period. PDT
will remain well within IFR, while RDM will be more obscure with
LIFR.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  32  28  32  27 /   0   0   0   0
ALW  33  30  33  29 /   0   0   0   0
PSC  36  33  35  32 /   0   0   0   0
YKM  34  28  32  26 /   0   0   0   0
HRI  37  33  37  30 /   0   0   0   0
ELN  33  25  32  25 /   0   0   0   0
RDM  37  16  40  19 /   0   0   0   0
LGD  46  27  40  25 /   0   0   0   0
GCD  48  29  47  26 /   0   0   0   0
DLS  39  33  35  31 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freezing Fog Advisory until 11 AM PST this morning for ORZ508-
     510-511.

WA...None.
&&

$$

SHORT TERM...78
LONG TERM....75
AVIATION...95