Area Forecast Discussion
Issued by NWS Spokane, WA

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657
FXUS66 KOTX 141216
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
416 AM PST Thu Nov 14 2024

.SYNOPSIS...
Thursday will be unsettled with widely scattered showers and
breezy southwest winds. Drier conditions return Friday with
areas of morning fog. Fog could be dense Saturday morning.
Heavy mountain will return Saturday night and Sunday with another
weather system moving through the area. There is a chance of some
light lowland snow Sunday morning. Next week looks much drier
with high pressure settling in.

&&

.DISCUSSION...
Today through Friday night: An elongated upper-level trough will
migrate through the region over the next 48 hours. Temperatures
aloft at 500 mb are cooling this evening and precipitation is
transitioning to more of a convective nature with on and off
showers. Showers this morning have been consistent in the Idaho
Panhandle, NE WA, and Cascade Crest due to the favored orographic
lift and aided by smaller vorticity lobes within the mean trof.
The pattern will not change much for today (THU) will be the case
through the day on Thursday however rainfall amounts will be more
chaotic and generally under a tenth to quarter of an inch. The
lowest probabilities for showers today will be in the lower Basin
between Ritzville to Wenatchee northward toward Omak given some
shadowing from the Cascades yet cannot guarantee a completely dry
day given the cooling aloft and steeper lapse rates. Snow levels
will remain around 3500-4500 feet. Temperatures this afternoon
will remain mild with readings in the 40s to lower 50s along with
breezy southwest winds gusting near 25 mph at times.

The trough axis will pass through overnight with calming winds and
decreasing shower chances. Given the recent rainfall, breaks in
the clouds will allow for fog to form rather quickly after dark,
some which could become dense. The main uncertainty comes with the
amount of clearing with models indicating a plethora of moisture
lingering within the 850-700 mb layer east of a line from Republic
to Moses Lake. A few light showers will linger over North Idaho,
Blue Mountains, and Northeastern WA on Friday but dry air
advection will continue under northwest flow aloft. PWATs will dip
down near 0.2-0.3". This should allow for more breaks in the
clouds and partial sunshine. Temperatures will cool around 5-8
degrees with highs cooling back into the 40s. Friday night will
deliver the highest probabilities for clearing skies and light
winds. This will bring a favorable setup for fog across the
lowlands of the Inland NW. Those with travel plans overnight or
early Saturday morning are urged to leave extra time and be
prepared for visibility restrictions. Conditions could also be
slick with a 70-90% chance for temperatures to cool below freezing
by sunrise Saturday morning for just about every site outside of
the L-C Valley. /sb

Saturday through Monday: Saturday will start off mostly dry under
a weak ridge, though mid-to-high clouds will increase as
subtropical moisture moves in. By the afternoon and evening, westerlies
will strengthen due to an approaching shortwave trough from the
Gulf of Alaska and widespread precipitation will form.

Lowland Snow: Saturday night will bring a chance for lowland snow,
though any accumulation in the Spokane metro is expected to be
light and mostly on grassy surfaces, as warmer road temperatures
will limit snow accumulations. Once cloud cover settles in on
Saturday, surface temperatures will have limited ability to drop,
especially with increasing moisture from the subtropical plume.
Initially, temperatures at the 850 mb level should support snow in
the Spokane/Coeur d`Alene area,  but overnight warming will
likely turn snow to rain. The best chances for significant snow
accumulation are in areas like the northern Pend Oreille River
Valley and Priest Lake area, where persistent fog and cooler 850
mb temperatures (around -5C) will keep warming at bay during the
day Saturday.

Chances for at least 2 inches of snow Saturday night will vary significantly
by location:
Spokane: 0%
Colville: 5%
Deer Park: 10%
Winthrop: 15%
Newport and Sandpoint: 30%
Republic: 40%
Coolin: 70%
Metaline: 80%

Mountain snow: Mountain passes and higher elevations could receive
over 3 inches of liquid precipitation. With snow ratios expected
between 10 to 15 inches per inch of liquid, the mountain passes
are likely to see some of the highest snowfall totals of the
season. Snow totals will be cut down a bit at Stevens pass
overnight into Sunday with strong warm air advection leading to a
changeover to rain. Models suggest a convergence zone forming over
Stevens Pass on Sunday behind the front passage, with wind gusts
reaching up to 40 mph. Snowfall will make travel through the
Cascades and Lookout Pass challenging.

Chance of snow :   6    12   24   36  Sat PM-Mon PM:
-----------------------------------------------
Stevens Pass   :  100%    90%  45%   15%
Washington Pass:  100%   100%  50%   10%
Sherman Pass   :   60%     5%   0%    0%
Lookout Pass   :  100%    70%  15%    0%

Monday through Thursday: As this system passes, strong high
pressure will build bringing drier conditions. Temperatures will
remain in the 30s and 40s, with lows in the teens to upper 20s.
This pattern could lead to air stagnation and fog, which will be
monitored. /DB

&&

.AVIATION...
12Z TAFS: Breezy south/southwest have maintained VFR ceilings for
most terminals along and south of Hwy 2 this morning. North of
highway 2, including Omak, Colville, and Sandpoint, MVFR ceilings
have become established. HREF has a 30-60% chance for these to
expand southward into COE, SFF, GEG, west toward Wilbur between
16-19Z for a few hours. The pattern is also conducive for passing
showers as an upper-level trough passes through. Challenging, low
confidence forecast overnight with potential for breaks in the
clouds to allow for fog to develop given lighter winds and very
moist boundary layer conditions but MVFR stratus is more likely
coming with 50-80% chance via the latest HREF.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is a variety of outcomes for Thursday night into Friday
morning from dense fog to persistent stratus for locations like
PUW, COE, GEG, MWH, and EAT. Many areas received appreciable
rainfall in the last 24 hours and it will not take much for fog to
develop with breaks in the clouds Thursday night. If the stratus
can develop between 2000-3000 feet, this would eliminate fog
potential with visibility mainly impacted from mist and more
likely to fall within the 4-6SM range. /sb

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https:/www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        48  30  42  27  40  30 /  60  40  30  20  10  80
Coeur d`Alene  45  32  42  29  39  31 /  80  50  40  50  20  80
Pullman        48  32  40  28  40  30 /  60  30  50  50  10  70
Lewiston       55  37  47  33  47  35 /  30  30  40  30   0  50
Colville       44  27  43  21  38  29 /  80  50  40  20  30  90
Sandpoint      41  32  41  28  37  31 /  90  80  60  50  40  90
Kellogg        42  32  41  31  36  31 /  90  50  60  60  40  70
Moses Lake     54  29  46  24  41  34 /  10  10   0   0  10  60
Wenatchee      51  34  48  27  41  34 /  30  20   0   0  10  70
Omak           49  32  46  25  41  31 /  30  20  10   0  20  80

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Winter Storm Warning until 4 PM PST this afternoon for Western
     Okanogan County.

&&

$$