Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 171016
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
216 AM PST Sun Feb 17 2019

.SYNOPSIS...
Periods of snow will continue over the Inland Northwest today,
with mainly light accumulations. Gusty north to northeast winds
return today, and may bring localized blowing and drifting snow
as cold temperatures return. Expect cold and dry weather Monday,
then a return to snowy weather by Tuesday through Wednesday and
possibly again by the end of the week. Cold temperatures will
continue this week.

&&

.DISCUSSION...
Today through Monday: A longwave trough continues to dominate the
weather pattern across much of the western and central US.
Several shortwave troughs are embedded within the longwave
pattern. The most noteworthy is a compact closed upper low
currently situated over southern Alberta, and slowly rotating
southward. Its associated frontal boundary is draped over northern
Idaho into Western Montana, and pushing south and west. Radar
imagery is picking up on light precipitation returns across NE
Washington and northern Idaho as of this writing. Farther south,
light precipitation in association with a rather unorganized area
of low pressure continues, mainly along the Blue Mountains and the
Camas Prairie.

Look for precitation coverage to increase through the course of
the morning into the afternoon as the Arctic frontal boundary
pushes southward. The system will slowly weaken as it does, but
not before dropping up to 2 inches of snow across portions of the
Idaho Panhandle and eastern Washington. The Camas Prairie will
remain under favorable northwest upslope flow through tonight, and
could see snow totals locally up to 6 inches. We will be issuing
a Winter Weather Advisory for this area.

As the frontal boundary pushes southward, locally breezy north to
northeast winds will be likely today into tonight. The Purcell
Trench of northern ID, Okanogan Valley, and portions of the
Columbia Basin will likely see the highest winds...though it
should be stated that these winds will remain significantly weaker
than what we saw a week ago. Even still, local areas of blowing
and drifting snow will be possible today.

As drier conditions settle in tonight, and the boundary layer
decouples, cold overnight temperatures will be likely the next
couple of nights. Widespread overnight lows in the single digits
to lower teens will be likely across the forecast area. We may see
a few pockets drop below zero, particularly over the higher
basins and lowland locations.
Dang

Tuesday and Wednesday: There is a consistent message within the
forecast models that our next bout of snow will impact the region
through this period courtesy of a shortwave dropping in from the
northwest. The system has sped up from previous runs and looks to
spread light snow into Eastern WA and N ID Tuesday afternoon which
then lingers in varying intensities through Wednesday before
clearing out from north to south Wednesday night. The initial band
of snow will be tied to the leading dynamics along the shortwave
then precipitation will become increasingly convective and showery
Wednesday and Wednesday night as a -34C cold pool, littered with
numerous spokes of energy, settles in. At this time, the heaviest
axis of snow accumulations looks to focus over Southeastern WA and
the lower Idaho Panhandle as well as the Cascade Crest. 2 to 4
inches will be common with locally heavier possible in the
Palouse, Camas Prairie, and Blue Mountains.
Ritzville...Spokane...Coeur D Alene...and Sandpoint will be on the
northern fringes of these heavier amounts with initial thoughts
of 1-2 inches. These amounts could go up with heavier showers on
Wednesday. Amounts taper off toward an inch or less in the lee of
the Cascades unless shower concentration on Wednesday is more
widespread than expected. General timing of this system would
suggest impacts to the Tuesday PM commute and into Wednesday.

Thursday: 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. Breezy north to northeast winds develop for Thursday
morning and wane by the late afternoon. While the threat appears
low...we will need to keep close eye on potential for localized
drifting issues with this weak push of northerly winds and renewed
light, fluffy snow accumulations.

Friday through Monday: Confidence remains above average that the
Northwest will remain in a colder than normal weather regime. In
regards to snow...models continue to waver with the evolution of
the next shortwave dropping in from the northwest. Subtle
differences with the interaction of this system and the offshore
ridge could equate to a big difference in snowfall amounts ranging
from little to nothing to moderate or even heavy amounts.
Duration of possible snow is also up in the air. Given the
uncertainty, the forecast continues to lean toward a multi-model
ensemble solution which keeps a mention of snow but carries low
confidence on exact timing/amounts. The large scale weather
pattern over the Ern Pacific and Pac NW Coast is one such that
model wavering is likely to continue for several more days as each
model suite attempts to resolve the complicated interaction
between a blocking high and shortwaves/cutoff lows. Stay tuned.
/sb

&&

.AVIATION...
06Z TAFS: Low clouds will linger over the region tonight to mid-
Sunday or with BL moisture under the long-wave trough and
unstable -shsn in the region. Some localized fog is possible away
from the precipitation threat. A backdoor cold front will start
to expand a broader threat of light snow in from north Idaho later
overnight into Sunday morning, increasing into the
COE/SFF/GEG/PUW toward 10-15z. Some heavier bursts of snow are
possible, first around GEG/SFF/COE in the morning and toward PUW
toward midday/early afternoon. The threat will expand toward
MWH/EAT but the risk is more limited, while it starts to decrease
from the northeast later in the day and evening. Expect MVFR/IFR
conditions tonight and Sunday morning, with the potential for some
improvement Sunday afternoon as some drier air tries to invade
from the Canada. Exceptions include the PUW/LWS where the boundary
will linger and low level moisture will be slower to erode. Some
localized blowing snow is possible around more open areas, but the
risk of impacts to TAF sites is limited. /Cote`



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        28   6  21   5  22  16 /  60  10   0   0  30  70
Coeur d`Alene  27   7  22   6  22  18 /  60  10   0   0  30  70
Pullman        28   9  21   6  23  21 /  60  30   0   0  20  90
Lewiston       34  17  27  12  29  26 /  50  30   0   0  20  70
Colville       34   7  29   7  27  12 /  60   0   0   0  30  70
Sandpoint      25  10  23  11  23  18 /  50   0   0   0  40  70
Kellogg        26   7  22   7  24  18 /  60  20  10   0  30  80
Moses Lake     32  13  24  11  24  16 /  10  10   0   0  40  40
Wenatchee      32  16  25  13  24  17 /  10  20   0   0  30  40
Omak           31  13  25  11  22  16 /  20   0   0   0  40  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 4 AM PST Monday for Lewis and
     Southern Nez Perce Counties.

WA...None.

&&

$$


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