Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 232358
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
358 PM PST Fri Feb 23 2018

.SYNOPSIS...
A series of storm systems will impact the Inland Northwest this
weekend into early next week with the potential for more snow,
breezy conditions and continued below normal temperatures for most
locations. The first round of snow will arrive over most of the
Inland Northwest this evening and continue at times through
Saturday. Another system will move into the region on Sunday.



&&

.DISCUSSION...
...Light to moderate snow tonight into Saturday. Snow and wind
Sunday...

Tonight through Sunday: This weekend will feature a pair of storm
systems. The first arrives this evening and lingers into
Saturday. A second system impacts the area Sunday. The general
storm track will be from the northwest which favors the the Idaho
Panhandle and Cascade Crest to receive the heaviest snow however
portions of the Blue Mountains and Palouse can also expect a
healthy dosage as well.

As of 2PM...a cold front and band of light snow was moving across
Central WA. This band will continue to march east toward the
Idaho Panhandle arriving close to rush hour and lingering into the
evening hours. Snowfall amounts will be extremely light in the
lee of the Cascades and Western Basin increasing around an inch or
two toward the Idaho Panhandle. Timing of this band into Eastern
WA and N ID could lead to slick conditions during the Friday
evening commute. A trailing cold core shortwave will track into
the region tonight. All models agree on weak surface low
developing with this wave and tracking west to east between
Highway 2 and I-90 across the Columbia Basin. Rapid cooling aloft
coupled with lift along the low will result in increasing snow
across much of the Idaho Panhandle and eastern reaches of WA with
a favorable setup for heavier snow bands. Snow intensities under
some of these bands may become moderate to heavy at times and
result in quick accumulations of 1-2 inches. Winds will become
breezy south and east of the surface low. Southwest winds of 10-20
mph with gusts near 25 mph will impact portions of Southeastern
WA and the lower Idaho Panhandle and could lead to patchy drifting
snow. Thinking the Camas Prairie may have the greatest threat
because of the additional 2-4 inches of fluffy snow that fell last
night. Snow from this first system will wane Saturday afternoon
with a brief break Saturday evening but a second round of snow and
winds arrives Saturday night into Sunday.

A second, deeper shortwave drops into the Northwestern US Saturday
night into Sunday. This is a much more dynamic system featuring a
stronger surface low across southwestern Canada and much tighter
packing of pressure gradients across the CWA. This equates to more
wind and much stronger orographic lift into the Cascades and into
the rising terrain of North Idaho, especially the Central
Panhandle Mountains. Precipitation will start off light Saturday
night with the passage of a warm front then look for snow to
increase early Sunday morning between 0400-1000 PST and continue
into the early afternoon. Snow amounts in excess of a foot are
expected for the mountains of southern Shoshone County and along
the Cascade Crest near Stevens Pass. Moderate to heavy amounts on
the order of 4-8 inches will also be possible in the rising
terrain of the Palouse, Camas Prairie, Blue Mountains, and into
the Silver Valley. Lighter amounts are expected northward and into
NE WA including the Spokane Area.

As for winds, we have increased winds for the Eastern Columbia Basin
including the Palouse and foothills of the Blue Mountains. Winds
will increase in these areas Saturday night into early Sunday
morning with speeds near sunrise on the order of 20-30 mph. Wind
gusts of 30-45 mph are expected but potential gusts of 50 mph are
not out of the question. This is because we see 50kts around
1500-2K ft AGL. Hi-res model data suggest this low-level jet will
remain decoupled from the surface Sunday morning and then weaken
closer to 40-45kts by the afternoon when gusts will have a better
potential to mix down to the surface but this will need to be
monitored closely. Exposed ridgetops will stand a better shot of
experiencing wind gusts in the 40-60 mph range. For the remainder
of the Columbia basin including the Waterville Plateau, expect
winds on the order of 15-25 mph with gusts closer to the 30-35 mph
range. /sb

Sunday night through Friday...Through the extended period it looks
like the pattern remains fairly progressive in northwest flow.
One upper low will exit the region on Monday, a second will drop
through the region Tuesday/Tuesday night, and a third will drop in
Thursday and Friday. There are some changes however, as the
models are indicating that the ridge that has been lingering out
near 160W will slowly begin to retrograde to the west. This in
turn will allow the storm systems to drop south along or even west
of the coast. This would keep the weather unsettled, but allow
temperatures to slowly creep back up to around normal by the end
of the week.

Sunday night and Monday...As mentioned above a deep and cold low
will track south on Sunday and exit the region Sunday night. The
focus of the precipitation will shift to the Cascade crest, The
Panhandle mountains, and south towards the Blue mountains and the
Camas Prairie. 5-6 inches of new snow will be possible in the
mountains above Clarkia and Avery, with a couple of inches of snow
for the Blues and up near Winchester by the end of the day
Monday. Strong gusty winds behind an exiting cold font will result
in wind gust 20 to 30 mph to continue through the night for the
Basin, the Waterville Plateau, the Palouse, and on ridge tops
through about midnight. Temperatures will remain on the cool side
of normal.

Monday night through Wednesday...After a brief break in the weather
Monday night the next low will take a similar track, with similar
results as the one this weekend. The lower east slopes and the
western basin will be mostly missed, but the Cascades and the
eastern half of the forecast area will have another chance to pick
widespread precipitation. Again it will be cold enough to support
mainly snow, with a rain/snow mix for a portions of the eastern
Basin south of highway 21. Northerly flow will keep temperatures
on the cool side of normal.

Thursday and Friday...This is out pretty far in the forecast but
we could see temperatures begin to warm to around normal by the
weekend. Model guidance is showing the next storm system tracking
south along the coast Thursday night before ejecting back to the
northeast Friday night and Saturday. This will allow the flow to
shift to the southwest and result in warming temperatures with a
much deeper Pacific moisture tap. This will keep the unsettled
weather in the forecast through the extended period. Tobin

 &&

.AVIATION...
00Z TAFS: A cold front is moving through the area at the time and
will bring a band of light to moderate snow to the eastern TAF
sites 00-03z. When the front moved through KMWH vis dropped to
1/2sm sn for an hour. The same is possible for KCOE-KGEG-KSFF-
KPUW. Snow will taper off to isolated -shsn through 10-11z with
cig/vis returning to VFR/MVFR. A surface low will come through the
region early Saturday morning and will result in bands of
moderate to locally heavy snow from 10-11z through 18-19z. This
will likely drop conditions back down to IFR at times. Then
returning back to VFR conditions with clearing from the west after
18z. Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        23  33  27  39  21  35 /  90  80  20  60  20  10
Coeur d`Alene  22  33  24  38  20  35 /  90  90  40  90  20  20
Pullman        23  34  27  38  23  34 /  80  90  40  90  50  20
Lewiston       31  40  33  45  27  41 /  50  80  20  60  50  20
Colville       21  35  25  40  17  37 /  80  50  20  70  20  10
Sandpoint      21  33  25  37  21  34 /  90  70  40  90  30  20
Kellogg        20  31  24  33  22  31 /  90 100  60 100  60  40
Moses Lake     26  41  32  48  23  44 /  10  20  10  20  10   0
Wenatchee      25  39  33  44  23  43 /  20  30  30  60  20   0
Omak           19  35  25  41  17  38 /  30  30  20  20  10   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 4 PM PST Saturday for Lewis and
     Southern Nez Perce Counties-Lewiston Area.

     Winter Weather Advisory until 1 PM PST Saturday for Coeur
     d`Alene Area-Idaho Palouse.

     Winter Weather Advisory until 4 PM PST Saturday for Central
     Panhandle Mountains-Northern Panhandle.

WA...Winter Weather Advisory until 4 PM PST Saturday for Lower
     Garfield and Asotin Counties.

     Winter Weather Advisory until 1 PM PST Saturday for Spokane Area-
     Washington Palouse.

     Winter Weather Advisory until 4 PM PST Saturday for Northeast
     Blue Mountains.

     Winter Weather Advisory until 1 PM PST Saturday for Northeast
     Mountains.


&&

$$



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