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FXUS66 KOTX 181046
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
246 AM PST Fri Jan 18 2019

.SYNOPSIS...
Snow showers will linger over the mountains this morning, followed
by a brief break this afternoon. Another round of mountain snow
and valley rain will arrive tonight bringing moderate to heavy
accumulations to the Cascades. The active weather pattern will
continue through the middle of next week with periods of snow in
the mountains and mainly rain in the valleys.

&&

.DISCUSSION...

Today: One weather disturbance will exit the Idaho Panhandle this
morning before the next one arrives tonight. Look for an
additional 1 to 3 inches of snow accumulation above 3000 feet in
the mountains of Shoshone county this morning with the most
significant impacts to Lookout Pass prior to sunrise. Temperatures
today will be about 5 degrees above average with afternoon
temperatures in the upper 30s to mid 40s across the Inland
Northwest. Low clouds and fog could linger into the late morning
or early afternoon across the West Plains toward the Waterville
Plateau with south winds pushing moist air (surface dewpoints in
the mid 30s) up the rising terrain over the chilly ground.

Tonight: A deep area of low pressure is forecast to make landfall
on the central BC coast prior to daybreak on Sat. This powerful
storm will produce widespread precipitation across the Inland
northwest tonight. Snow levels will likely be low enough for 1 to
4 inches of snow accumulation in the Methow Valley overnight with
similar amounts above 2000 feet around Leavenworth. Motorists with
plans to travel over Stevens, Blewett, Loup Loup, or Sherman Pass
tonight should be prepared for winter driving conditions. For the
valleys of northeast Washington into the Idaho Panhandle, a mix
of rain and wet snow is expected. Elevations above 3000 feet will
have the best shot of a couple inches of wet snow while the
majority of the valleys probably won't get much more than an inch.

Saturday: Friday night's wet frontal system will produce valley
rain and mountain snow over the Idaho Panhandle Saturday morning
before precipitation decreases to showers in the afternoon.
Remnants of this front are forecast to stall over northern Oregon
and central Idaho Saturday afternoon and may lift northward
Saturday night into Sunday. At this time, there is some
uncertainty on how far north this front will lift Saturday night.
A blend of models brings a 20 to 30 percent chance of rain and
snow as far north as the Canadian border by Sunday morning, a low
confidence forecast. /GKoch

Sunday and Sunday Night: A trough of low pressure will move in off
of the eastern Pacific. There will be portion of the energy
associated with this trough that traverses right up across the
southeast portion of the forecast area. The stronger dynamics
aloft will actually miss the Inland Northwest and dive down across
southern OR and into CA. However, the energy that does impact the
Inland Northwest is potent enough to spin up a surface low over
northeast OR Sunday morning that moves into the southern ID
Panhandle by Sunday afternoon. The 00Z GFS has the strongest
surface reflection and is further north with best potential for
winter impacts across eastern WA and into the central to northern
Idaho Panhandle. The 00Z ECMWF, Canadian and NAM solutions are a
bit weaker and further south with precip primarily falling
southeast of a line from Ellensburg to Sandpoint. I treated the
GFS solution as an outlier holding on to the highest precip
chances across the southeast portion of the region and decreased
precip chances across the northwest portion of the region. Snow
levels will be between 3000 and 4000 feet during the day on Sunday
and then drop Sunday night as this system exits with minor valley
accumulations possible at that point. Main impacts look to be over
the passes, including Lookout Pass and over the Camas Prairie,
especially as temperatures cool by Sunday evening.

Monday through Friday: Colder and drier air will push in across
the region out of Canada behind the exiting weather system Sunday
night. This will set up a potentially more significantly impactful
winter storm system on Tuesday. Snow levels will be down to valley
floors with heaviest precipitation looking to move in during the
nighttime hours. The shortwave disturbance will push in out of a
northwest flow pattern. This kind of flow pattern typically favors
the Idaho Panhandle. However, models indicate frontogenesis strong
enough to spread precip across the basin and into the
Spokane/Coeur d'Alene corridor and on the Palouse. The Tuesday
evening and/or Wednesday commutes could be messy with winter
driving conditions possible, mainly along and north of the Highway
2 corridor. There is high confidence for drier conditions
Thursday and Friday. /SVH

&&

.AVIATION...
06Z TAFs: Small scale disturbances moving through the cold and
conditionally unstable airmass over the aviation area are
producing rain and snow showers tonight. In addition to the
showers the boundary layer remains very saturated from all the
recent precipitation, hence IFR/MVFR ceilings and visibilities due
to stratus and/or fog or produced by the showers that are moving
through are a possibility tonight into early tomorrow. In addition
another synoptic scale low pressure system will bring stable rain
with high mountain snow into the region and spread it to the north
and east starting as early as 2Z Saturday near KEAT and KMWH and
near 6Z Saturday and beyond for remaining TAF sites to the east
which would include KGEG,KSFF,KCOE,KPUW, and KLWS. /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane 39 33 42 32 37 25 / 10 100 70 30 50 30
Coeur d'Alene 39 34 41 32 37 28 / 30 90 90 30 50 40
Pullman 42 35 43 35 39 30 / 10 100 70 40 80 60
Lewiston 48 39 49 38 46 35 / 10 90 60 50 80 60
Colville 38 32 42 29 40 21 / 20 90 70 20 20 20
Sandpoint 37 33 37 32 37 27 / 50 90 100 30 40 40
Kellogg 38 33 41 33 38 30 / 60 90 90 50 70 60
Moses Lake 44 36 47 33 40 28 / 0 80 10 20 40 10
Wenatchee 40 33 43 31 37 28 / 10 100 10 20 30 10
Omak 39 33 41 28 37 24 / 10 90 30 10 10 10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 7 AM PST this morning for Central
Panhandle Mountains.

WA...None.

&&

$$
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