Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 212353
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
353 PM PST Sat Jan 21 2017

.SYNOPSIS...
Periods of light snow are expected this weekend over the Inland
Northwest. Our temperatures through the weekend will be relatively
mild with afternoon readings in the 30s and low 40s. A drier and
cooler weather pattern is expected next week with the possibility
of deteriorating air quality as the week wears on.

&&

.DISCUSSION...

Tonight...General low pressure off the coast juxtaposed against
higher pressure over the interior continues to allow for a southwest
to northeast oriented path for weather disturbances to pass over
Eastern Washington and North Idaho. Current radar imagery shows
one such disturbance exiting the North Idaho Panhandle while a
second similarly structured disturbance is moving through Oregon.
Between these two disturbances is an area of surface based
convective showers that is making similar movement to the
north/northeast. Expectation is the clutter of having these three
areas of precipitation moving through will allow for moderate to
high chance pops over most of the forecast area tonight. In
addition abundant low level moisture remains so patchy fog and low
clouds are likely to remain in the typical locations tonight.
/Pelatti

Sunday and Sunday night: An occluded front will bring a round of
mountain snow and a rain/snow mix to the valleys. Low pressure
will remain offshore in the eastern Pacific with the circulation
center out at 130W 45N. The timing of the front will be Sunday
morning for the east slopes of the northern Cascades to late
Sunday afternoon/evening for much of the ID Panhandle.
Frontogenesis will weaken with time as the front moves further
away from the parent low. this will result in the bulk of the
precip falling over the western portion of the forecast area.
Easterly flow will also will also create favorable upslope flow
into the east slopes of the northern Cascades. Models show the
axis of highest precip occurring just east and away from the
Cascades crest. This is likely due to an artificial slope being
created by the colder air damned up against the Cascade Mtns. The
relatively warmer and more moist air riding up ahead of the front
is achieving its best lift along an axis from around Leavenworth
-Wenatchee to Winthrop-Conconully. Precip amounts will become
gradually less further east toward the ID Panhandle; two reasons
for this: (1) dynamics are becoming weaker and (2) low level
easterly winds will create some downsloping off of the higher
terrain.

Precip type will be a challenge with this weather system. We are
not expecting any freezing precip, but snow levels will vary quite
a bit where much of our population resides. Confidence is high
that much of the lower portions of the upper basin will see rain
(generally south of I-90). Then there will be a rain/snow mix
across the upper portions of the basin and into the surrounding
mountain valleys, especially those below 2,000 feet in elevation.
Areas just above the 2,000 foot level (e.g. West Plains and
South hill) should at least start out as snow, but then
transition to a rain/snow mix or rain during the afternoon. Models
have also exhibited a cold bias of late, so I have increased snow
levels a bit more and we may still be a bit too low.

The east slopes of the northern Cascades will see between 2-4
inches in the valleys and locally up to 6 inches. The Wenatchee
Area, Waterville Plateau, Okanogan Valley/Highlands, Northeast
Mtns and central to northern Panhandle will see around 1 to 3
inches in general. These valleys further west closer the Cascades
will see a better chance for snow accumulations closer to the 3
inch mark. The amount of snow that falls in the ID Panhandle will
suffer since it will be falling during the afternoon.

The front will clear the region overnight with fog expected to
form over the basin as mid to high level clouds clear out. I
expect this fog to expand into the surrounding mountain valleys
late Sunday night into early Monday morning. /SVH

Monday through Saturday...A fairly quiet and cool weather regime
is on tap for next week. Models are in decent agreement in exiting
an upper level trough early in the week and replacing it with a
ridge through next weekend.

Monday and Tuesday the forecast area will be in the relatively
quiet col region of a broad upper trough...no major weather
systems and predominantly dry...but the mountains and in
particular the Panhandle high terrain will be subject to some
snow showers which will be capable of periodic minor
accumulations.

After that...Wednesday through Saturday...The upper rideg will
assert itself with dry conditions but an increasingly strong
inversion over the region. Thus a typical January inversion
scenario is expected with increasing low clouds and at least
patchy freezing fog each day with temperatures below normal but
not unusually cold for deep winter. Winds will be light and
variable under this inversion...and this lack of ventilation and
capping inversion will lead to deterioration of air quality to the
point where Air Stagnation Highlights will probably become
necessary as the week wears on. /Fugazzi

&&

.AVIATION...
00Z TAFS: An upper level low off the Pacific coast will send two
waves of moisture along a pair of occluded fronts form southwest
to northeast through the forecast area. The first wave will pass
through tonight. This wave will be the weaker of the two but still
likely produce MVFR ceilings and vis in -SN at all TAF sites. A
period of IFR conditions between systems is probable especially
at the KGEG area TAF sites where low level flow will favor
upslope stratus Late tonight and Sunday morning...while KPUW and
KLWS will benefit from downslope easterly winds minimizing the
stratus threat. The second and stronger wave will move through on
Sunday late morning through the afternoon with more MVFR or IFR
conditions especially at the KMWH and KEAT TAF sites where upslope
flow into the Cascades will enhance lift along the front. /MJF


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        31  37  26  32  21  30 /  50  90  80  10  20  10
Coeur d`Alene  31  36  25  34  22  31 /  50  70 100  10  30  20
Pullman        33  38  26  33  23  30 /  30  90  50  10  30  30
Lewiston       32  41  28  35  26  34 /  20  50  20  10  30  30
Colville       31  35  30  33  20  29 /  60  60 100  20  20  10
Sandpoint      31  35  26  33  22  31 /  50  30  90  10  30  20
Kellogg        29  33  26  31  22  29 /  30  50 100  10  30  40
Moses Lake     32  35  27  33  19  30 /  50 100  10  10  10  10
Wenatchee      31  35  26  31  21  28 /  80 100  10  10  10  10
Omak           33  34  28  33  19  30 /  60 100  80  10  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$



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