629
FXUS66 KOTX 181213
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
413 AM PST Mon Feb 18 2019

.SYNOPSIS...
Cold and dry weather are expected today and tonight. Another
storm system will bring snow Tuesday through Wednesday with the
potential for heavy snow accumulations over southeastern
Washington and lower Idaho Panhandle. Another round of snow is
possible by the end of the week into the weekend as cold
temperatures persist.


&&

.DISCUSSION...
Today and Tonight: Drier northerly flow has taken hold across much
of the region in the wake of yesterday`s frontal boundary passage.
Radar imagery is hinting at a few light snow showers or flurries
along a N-S oriented axis from Republic to Walla Walla early this
morning as a weak deformation band passes through. Additionally,
snow showers continue across the Camas Prairie under favorable
upslope northwest flow. Otherwise quieter weather has settled in
across the Inland Northwest. Drier conditions and pockets of clear
skies have allowed for strong radiational cooling this morning,
particularly in wind-sheltered locations. As a whole, most of the
region should be dipping down into single-digits to the lower teens
this morning, with a few pockets of sub-zero temperatures.

Mainly quiet weather is expected to continue today and into tonight.
Winds will continue to diminish today and into tonight. A weak wave
is expected to pass through the region tonight. Forcing is minimal,
but may be enough to generate isolated showers over the NE
Washington & N Idaho mountains. Increasing cloud cover may also
inhibit some of the radiational cooling that we`re seeing tonight.
Boundary layer winds are expected to become more of a moist
southwesterly direction tonight, which may result in a few pockets
of freezing fog.
Dang

Tuesday and Wednesday: A potent shortwave currently north of the
Aleutian Islands drops into the Northwest Tuesday afternoon and
lingers into Wednesday delivering the next round of snow for the
Inland NW. We should see a general top down moistening and onset
of light snow over Central WA shortly after midday Tuesday before
spreading into the eastern third of WA and N Idaho by the late
afternoon and early evening. This is looking to impact the evening
commute. This first band of snow will clear out Central WA rather
quickly with less than an inch expected in the lee of the
Cascades but this will not be the case for the eastern third of WA
and North ID. As this first band of snow clears eastward...the
air mass rapidly cools aloft with 500mb temperatures plummeting
near -34C while the midlevel dynamics drop in from the northwest.
Models are also showing a 1008-1010mb surface low which looks to
be deepening slightly 1-3 mb while crossing into SE WA and NC ID.
This will be a good setup for bands of heavier snow across the
Palouse, Blue Mountains, Camas Prairie, and southern reaches of
Shoshone County. Thinking this activity will also impact the
foothills of the Blue Mountains and L-C Valley but exact amounts
immediately downstream of the Blue Mountains could be impacting by
downsloping winds leading to varying amounts. Nonetheless,
confidence is increasing for moderate to heavy snowfall in these
areas and winter storm watches have been issued. Lighter snow
amounts of 1-3 inches will be common across NE WA and N ID. Should
see a solid inch with the steadier snow Tuesday afternoon/evening
then clusters of convective showers tied to vorticity lobes
spinning over these areas will bring additional accumulations of
1-3 inches. This showery activity is typically more variable in
nature similar to what we experienced in the last 36 hours which
resulted in snow totals varying from a few tenths to 4 inches.

As the system sags south Wednesday, some of these showers will rotate
back into Central WA with renewed the threat for light snow
activity. This will draw drier, continental air in from the north
and bring another push of north to northeast winds through the
Okanogan Valley, North Idaho, and into the Columbia Basin
Wednesday night. Speeds do not look overly impressive but could
result in drifting snow due to the cold temperatures and light
fluffy nature. Snow showers will be more persistent along the
Cascade Crest and expected to have moderate impacts on the passes.

Thursday and Thursday night: A few light snow showers will linger
into Thursday morning however high pressure strengthening aloft
coupled with a resurgence of dry, chilly continental air will
deliver a mostly dry day with increasing sunshine. Breezy north to
northeast winds Thursday morning will wane by the late afternoon
but drifting snow could remain an issue throughout the morning
hours. Thursday night is setting up to be very cold with fresh
snow, clear skies, and light winds. Would not be surprised to see
single digit temperatures in many locations before midnight if the
clouds from the incoming system hold off as the GFS is showing.
/sb

Friday through Monday: Our brief dry period will likely come to an
end on Friday, as the shortwave ridge moves eastward, and our next
trough drops southeast from the Gulf of Alaska. The 00z GFS, ECMWF,
and Canadian models have come into much better agreement than
previous runs, with warm frontal precipitation spreading across the
region during the latter half of Friday and continuing into
Saturday. Successive reinforcing waves will likely continue to move
through the region, and keep unsettled weather going through the
weekend, and possibly into early next week. At this stage the
airmass looks cold enough to remain primarily snow across the
region, with the exception of the Lewis-Clark Valley, which could
see periods of both rain and snow.
Dang

&&

.AVIATION...
12Z TAFS: A drier airmass has moved into the region, resulting in
VFR conditions across area TAF sites. Isolated snow showers will
continue in eastern Washington through the morning, but are
unlikely to impact TAF sites. Winds will become light by this
afternoon, and shift to the southwest tonight. This may bring a
return to patchy fog and low clouds by Tuesday morning.
Dang

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        22   8  24  17  29  16 /   0  10  60  90  30  10
Coeur d`Alene  23   9  24  19  30  17 /   0  10  60  90  30  10
Pullman        21  10  26  23  29  17 /   0   0  50 100  80  20
Lewiston       28  15  32  28  34  23 /   0  10  30  90  70  30
Colville       29   9  28  14  35  14 /  10  10  50  80  10   0
Sandpoint      23  13  24  19  30  19 /   0  10  60  90  30  10
Kellogg        23  10  24  20  31  19 /   0  10  40  90  70  20
Moses Lake     26  13  26  18  29  16 /   0  10  20  30  40  10
Wenatchee      26  15  26  19  30  17 /  10  10  20  20  40  20
Omak           26  14  24  17  30  18 /   0  10  20  20  20  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Central Panhandle Mountains-Idaho Palouse.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Lewis and Southern Nez Perce Counties.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Lewiston Area.

WA...Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Washington Palouse.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Northeast Blue Mountains.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for Lower Garfield and Asotin Counties.


&&

$$