-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KOTX 261235
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
435 AM PST Sat Nov 26 2022

.SYNOPSIS...
Motorists will encounter snow in the mountains this evening and a
mix of rain and snow in the lowlands. Moderate to heavy snow will
fall in the Cascades and Idaho Panhandle mountains late tonight
into Sunday. Temperatures will be colder next week, with the
potential for lowland snow during the middle of the week.

&&

.DISCUSSION...
Today: Wave is quickly exiting the region. Have decreased our
chance of snow for this morning across the ID Panhandle as well as
the Cascade mountains. Forecast challenge for today will be
figuring out the stratus and fog situation. Patchy fog and stratus will
continue through the morning hours across the region and then
slowly dissipate through the afternoon as sunny skies above the
stratus deck will provide an opportunity for drying and for it to
dissipate. Winds will be light through the day and we will see
temperatures in the 30s across the valleys which is average for
this time of the year.

Tonight and Sunday: The next wave will move in this evening
bringing another round of winter precipitation and winds. Snow
will start in the evening across the Cascades and north ID
mountains. Precipitation will then spread south through the
overnight hours. The caveat is there is a strong 120 kt jet that
moves in overnight. Our winds will begin to increase late this
evening and continue to increase through the night. The winds will
be from the south or west, depending on location. The westerly
winds will shadow out the Moses Lake area and only brings the
potential for brief rain or snow to Wenatchee. Meanwhile the
Cascade mountains will get slammed. Stevens Pass has a 95% chance
of 12 inches of snow and a 65% chance of 18 inches. Have upgraded
the watch to a warning for this evening through Sunday morning.
HREF model is showing good probabilities of an inch an hour
accumulation occurring through the overnight hours. Travel could
be quite difficult if you plan to be on the roads Saturday night
and early Sunday morning.

Let`s go back to the winds for a moment...there is a 90% chance or
higher of seeing gusts to 40 mph for Ritzville, Spokane, Couer
d`Alene and Pullman. A 50% chance of 40 mph gusts for Moses Lake,
and a 35% chance for Wenatchee. Gusts over 45 mph have the highest
probabilities around Lincoln and Adams county as well into Spokane
and the Couer d`Alene area with about a 50-60% chance. These winds
will be strongest overnight and through about noon and will then
decrease through the afternoon. The Cascade mountains, The Blues
and parts of the central ID Panhandle mountains will see gusts in
excess of 50 mph...but that is for locations generally above 4000
ft.

The snow moves into the Spokane/COE area overnight and Sunday
morning. Accumulations will be light with about a half an inch for
Spokane and near an inch for COE. Valleys to the north, locations
such as Newport, Sandpoint, Bonners Ferry and Ione will see 1 to 2
inches of snow.

Snow will start in the central ID Panhandle mountains early Sunday
morning. Have issued a winter storm watch for Sunday.
Accumulations in the valleys will be about 1 to 2 inches with 4 to
7 in the mountains. There is a 90% chance of 6 inches and a 70%
chance of 8 inches for Lookout Pass. Given the return holiday
travel wanted to put out this watch so people are aware and can
make plans accordingly. Amounts and rates won`t be as heavy as the
Cascades, but a travel impact nevertheless.

Sunday Night and Monday: The wave moves south Sunday night and
Monday but we get a second wave to move through, mainly impacting
the southern portion of Washington and the ID Panhandle. The Blue
Mountains could see snow begin Sunday morning, but really picking
up during the evening and continuing through Monday. Have issued
a watch for them as well. There is an 90% chance of 8 inches and a
75% chance of 12 inches.

Some of the ensembles as well as the NAM is spinning up a surface
low across southern WA Monday morning. This will need to be
monitored as this could produce higher snow amounts than what is
currently in the forecast. Regardless of the low position, it
looks like the Palouse could see snow throughout the day with a
70% chance of 2 inches of snow, and a 30% chance of 4 inches of
snow. /Nisbet

Tuesday...This period will be quietly enough as the remnants of
the Sunday/Monday system drop south and east of the region. But
that quiet will be eroded as the next upper level trough moves
into the region.

...Widespread moderate to locally heavy snowfall looks possible
late Tuesday through early Thursday...

Late Tuesday night through Thursday morning...The models are in good
agreement that a significant upper level trough will move toward
the Washington coast during this period. The big question deals
with timing and impacts. The Euro ensembles and the EC
deterministic model show a deep surface low moving to the northern
tip of Vancouver Island late Tuesday afternoon and then across
southern BC through Wednesday. This in turn places a slow moving
east-west band of snow across the northern half of our forecast
area due to persistent isentropic ascent. This notion is shared
more or less by the Canadian ensembles. Meanwhile the GEFS, shows
a much slower solution with the upper level trough remaining well
off the coast through much of Wednesday and not really bringing
significant snow into the picture until Wednesday afternoon and
into the overnight hours. If we simply bypass the ensemble means
and look at this through a cluster analysis of all the ensemble
runs about 75% of the run support this earlier Canadian/ENS
solutions which suggests we could be looking at widespread snow
across much of the region, including the Spokane/CdA area. Right
now we are forecasting amounts ranging from 4-7 inches in the
metro area, with amounts ranging from 4-9 inches from Nespelem to
Chewelah to Sandpoint. If we look strictly at the chances for 6”
of snow or more for Wednesday into early Thursday morning, the
Spokane/CdA area has a 50-55% chance of exceeding that mark, with
between a 60-70% chance for Sandpoint, Colville, Chewelah, and
Priest Lake. Needless to say the percentages are even higher for
Stevens and Lookout Passes. These numbers are from the NBM 4.1
which is a little snowier than the 4.0...but the trend over the
last few runs is getting snowier. It could be quite messy to say
the least for any travel plans. As for precipitation type there is
no doubt this will fall as snow, over much of the area, with the
small exception of some rain/snow over the LC Valley and extreme
southern portion of the Columbia Basin.

For Thursday afternoon into Friday...provided the EC/Canadian solutions
prove correct...we will see the upper level trough axis push
inland and weaken on Thursday, while the GEFS is stronger and
slower. In any case although it wouldn’t dry out the forecast it
would transition to more of a hit or miss snow shower event with
steep lapse raters through the dendritic layer. This would likely
favor the Idaho Panhandle with more showers at the Cascade Crest.
By Friday into Saturday another trough builds off the coast, but
this one is expected to dive much farther to the south. Thus if we
see any snow it will likely be quite light with much heavier
amounts expected over Oregon.

Based on all the uncertainties with the depth and timing of the
upper level trough, there are big differences in the temperature
forecast. For instance, the faster Canadian/ENS solutions bring a
warm sector into the region on Wednesday with highs into the upper
20s to mid 30s, whereas the GEFS doesn’t produce much of a warm
sector at all and as a result has highs in the upper teens to mid
20s. And this trend continues through much of the week. fx

&&

.AVIATION...
-- Changed Discussion --
12Z TAFS: IFR/LIFR fog and stratus will continue through the
morning hours at terminals. The exception is LWS and EAT where VFR
conditions are expected. Probabilities are high IFR/LIFR will
continue through the morning and then begin to see improving
conditions through the afternoon. The precip previously in TAFs
for aft 00Z has been delayed and not expected till towards 12Z or
after. Winds will increase aft 06-09Z which will help improve vis
and cigs further.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        36  31  35  18  25   9 /   0  40  70  20  20  10
Coeur d`Alene  36  31  35  19  25  10 /   0  60  90  30  20  10
Pullman        38  29  37  22  28  12 /   0  10  80  60  50  10
Lewiston       44  36  41  30  33  22 /   0  10  70  60  60  20
Colville       34  24  35   7  23   1 /   0  60  50  10  10  10
Sandpoint      34  31  34  18  24  10 /  10  80  90  20  10  10
Kellogg        34  32  32  21  24  10 /  10  60 100  40  30  10
Moses Lake     37  28  43  21  30  11 /   0  10  10  20  20  10
Wenatchee      39  32  39  24  30  16 /   0  30  20  40  20  10
Omak           35  26  34  16  22   8 /   0  50  30  20  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Watch from late tonight through Sunday evening for
     Central Panhandle Mountains.

WA...Winter Storm Watch from Sunday morning through Monday evening
     for Northeast Blue Mountains.

     Winter Storm Warning from 7 PM this evening to 10 AM PST Monday
     for Western Chelan County.

&&

$$