Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 102254
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
254 PM PST Sat Dec 10 2016

.SYNOPSIS...
Widespread light to moderate snow overnight through Sunday with
heaviest accumulations on the Cascade Crest and central Idaho
panhandle. Brisk dry north winds are expected Monday down the
Okanogan Valley the will spread out over the western basin.
Temperatures will become very cold by Tuesday and will continue
through next week. Many areas will see overnight temperatures fall
into the single digits with some locations seeing temperatures
below zero for early to mid week.

&&

.DISCUSSION...
Tonight: Watching the radar begin to fill in on the west side of
the state. Snow will begin again along the crest over the next
hour or so. It will snow all night in the Cascades. Decent
southeast flow into the valleys will promote light snowfall
through the evening hours. Then overnight the flow will veer to a
more southwesterly flow and snow will decrease. But before it is
over the Cascade valleys could see 2 to 5 inches. The methow
valley will see the least amount of snow...with about 2 inches
possible. The mountains tonight could see 5 to 10 inches with
locally higher amounts right at the crest or a mile or two
eastward.

The snow will spread eastward through the evening hours. The main
snow band should be to the Spokane/COE area around 8pm, and will
continue through the night. However radar is showing a weak
disturbance that is perhaps mixing up the stratus a bit, and could
get some very light snow showers that should`t provide much
accumulation before 8pm. Numerous winter weather advisories have
been issued with a warning for the central ID panhandle and the
Idaho Palouse. The models the last few days have been consistently
showing higher snow totals possible for this area. It may even
extend toward Pullman...but tonights snow amounts wouldn`t warrant
a warning.

Today`s temperatures were not realized because of the widespread
low clouds across the region. So lowered temperatures for tonight
given the already low temps across the region.

Generally tonights snow across the valleys will range from a trace
to a half an inch for the Moses Lake...Waterville
Plateau...Wenatchee and Okanogan Valley. The valleys east of a
line from Ritzville to Republic will see about 1 to 2 inches. Some
valleys in the ID Panhandle will see locally higher amounts.
Please continue to monitor our webpage for the latest totals.
/Nisbet

Sunday through Monday night: An active winter pattern will
continue across portions of the Inland NW as a pair of
disturbances bring two more shots of snow...then we will
transition toward a drier and colder weather regime.

A strong 120+kt jet oriented from offshore waters through northern
Oregon...and into the Intermountain West will keep the Inland NW
on the cool and unstable side of the jet and allow a pair of
disturbances to spin up and pass through the region. Snow showers
will be in the forecast for just about every location however the
focus for bands of snow capable of moderate accumulations will be
across Southeastern WA, Idaho Panhandle, and along the Cascade
Crest and adjacent upper valleys. In SE WA and ID...the heaviest
snow looks to be within a region along and south of I-90...north
of Lewiston and east of line from Davenport to Ritzville. Snow and
snow showers will taper off from north to south Monday as colder
and drier floods in from Canada promoting gusty north winds down
the Okanogan Valley...Columbia Basin...and northern mountains.

changes to the forecast were to increase snow amounts for the
Palouse and Central Panhandle Mountains, add blowing snow for the
higher benches of the Palouse each Sunday morning and evening, and
adjust temperatures down for Tuesday morning.

* Timing: One wave of snow will be on the way out Sunday morning.The
next round will develop Sunday afternoon and persist well
through the night and into Monday morning. The modified Arctic
front will drop into North-Central WA Sunday evening. The front
will act as another boundary to keep snow showers ongoing,
especially upon reaching the deeper moisture across the Columbia
Basin and Palouse but we should see most snow end by Monday
evening.

* Snow Amounts: For 30 hour snowfall amounts, 4-8 inches in higher
  benches of the Palouse going into the Central Panhandle Mtns.
This includes locations like Rockford, Oakesdale, Palouse,
Tensed, Potlatch, Pullman-Moscow, and into St Maries. Amounts
increase further for the mountains, especially south of I-90
where closer to a foot or more. In Northeastern WA, far N Idaho,
Spokane-Cd`A, Eastern Columbia Basin east of Davenport to
Ritzville and outside the aforementioned axis of heavier snow
will be more in the 1-3 range. Lower amounts are expected in the
L-C Valley due to warmer temperatures and potential for wet
accumulations or even rain/snow mix at times. Less than an inch
for the Hwy 97 corridor, Western Columbia Basin, and eastern
reaches of the Cascade East Slopes. Closer to the Crest, an
additional 6-12 inches is possible with lighter amounts into
Leavenworth, Plain, and Lucerne; call it 2-5 inches.

* Winds: Breezy southwest winds of 10-15 coupled with gusts to 25
mph will blow across SE WA and into the Idaho Palouse Sunday
morning. Winds will weaken and switch more southerly late Sunday
afternoon then pick up again Sunday evening with similar speeds
as the morning. This could result in areas of blowing and
drifting snow across the Palouse and along the US95/SR195
corridors. Confidence would be high except uncertainty degrades
some due to temperatures warming into the lower 30s. Confidence
is moderate to high for gusty north winds down the Okanogan
Valley Sunday night into Monday. Speeds will approach 15-20 with
stronger gusts. Breezy N winds will also impact the northern
mountains during this time-frame but speeds should be lower.

* Temperatures: Sunday will feel quite warm to many folks as we
  hit the upper 20s and lower 30s across many locations. Locations
  along the Snake River Valley will have a decent shot of warming
  into the upper 30s. Snow levels will increase some for these
  locations but looks as if the wetbulb temperatures will be close
  enough to 33F to keep mention of rain/snow mix or snow with
  minimal accumulations. This warming will be brief with
  temperatures region-wide cooling below freezing Sunday evening.
  Breezy north winds Sunday night should keep temperatures from
  plummeting for Monday morning but highs will only top out in the
  20s Monday then as winds decrease Monday night and skies begin
  to clear out...we will see an increasing potential for single
  digit temperatures. /sb

Tuesday through Saturday

...High Probability of Below Average Temperatures Late Next
Week...

The highlight of this period will be cold temperatures and a
slight chance of snow...mainly for the southern third of our area
of responsibility. Cold arctic air will remain in place through
the early part of next week. We made very minor tweaks to the
current forecast temperatures. While some guidance is going colder
than our forecast, the limiting factor is cloud coverage.
Currently GFS suggesting some mid level clouds will stick around
as a system undercuts us which would help keep temperatures from
bottoming out.

That changes late in the work-week as dry northerly flow aloft
will reinforce the cold air as well as push clouds out of the
region. Long range (next weekend) GFS temperatures are very cold.
Climate Prediction Center`s 6-10 and 8-14 day outlooks reinforce
this idea of high probability of below average temperatures. A
peak at the ensemble return interval table is hinting at about a
once in 5 year event. Certainly things may change but these
temperatures (possibly sub- zero) are going to need to be watched
carefully. In addition to the snow over the next couple of days,
we will begin advertising this arctic intrusion in the Hazardous
Weather Outlook and weather stories. /AB

&&

.AVIATION...
00Z TAFS: Very light snow or flurries is falling out of some of
the stratus across the upper columbia basin and into NE WA. The
main band of snow is currently moving over the Cascades and will
bring widespread snow west to east through the evening hours
starting with KEAT arnd 00Z and to KGEG by 03Z. For eastern TAF
locations the snow will be continue through the night changing
over to -shsn btwn 09-13Z. Vis should remain MVFR through the
event, but cigs could go down to IFR. The potential exists for
some LLWS for KPUW btwn 12Z-16Z, but confidence wasn`t high so
haven`t added it to the TAF yet.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        22  33  23  25   2  11 /  80  60  50  10  10   0
Coeur d`Alene  23  33  23  27  -1  15 /  90  80  70  20  10  10
Pullman        25  34  27  28   7  17 /  80 100  80  70  30  10
Lewiston       28  37  27  34  14  23 /  50  40  20  30  30  10
Colville       25  30  22  25   2  15 /  80  30  20  10  10   0
Sandpoint      23  31  24  28   0  14 /  90  60  60  20  10  10
Kellogg        23  31  23  26  -3  15 / 100 100  90  40  20  10
Moses Lake     21  33  20  28   8  19 /  40  30  30  20  10  10
Wenatchee      20  33  24  28   7  21 /  70  20  20  20  10  10
Omak           21  28  21  23   5  18 /  80  10  20  10   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory from 7 PM this evening to 4 PM PST
     Sunday for Northern Panhandle.

     Winter Storm Warning from 10 PM this evening to 10 AM PST Monday
     for Central Panhandle Mountains-Idaho Palouse.

     Winter Weather Advisory from 7 PM this evening to 10 AM PST
     Sunday for Coeur d`Alene Area.

WA...Winter Weather Advisory from 7 PM this evening to 10 AM PST
     Sunday for Spokane Area-Upper Columbia Basin.

     Winter Weather Advisory until 10 PM PST Sunday for East Slopes
     Northern Cascades.

     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Monday for Washington Palouse.

&&

$$


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