Area Forecast Discussion
Issued by NWS Spokane, WA

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691
FXUS66 KOTX 192336
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
336 PM PST Mon Feb 19 2018

.SYNOPSIS...
Tonight will be very cold with many locations near to below zero.
Cold and generally dry conditions will persist throughout the
week outside some passing light snow showers at times. A stronger
storm system will impact the region next weekend bringing the next
chance for appreciable snow.

&&

.DISCUSSION...
Tonight through Wednesday: The big story will be cold temperatures.
Several records might be broken by Tuesday morning as a very dry
Arctic air mass resides over the region. With the addition of
clear skies and light winds, maximum radiational cooling is
expected result in plummeting temperatures upon sunset. Overnight
lows will be in the single digits to low teens across the Basin
while mountain valleys and areas of the Palouse with fresh snow
dip below zero.

The only caveat regarding overnight temperatures will be a few clouds
developing between 3-4K ft AGL as 850mb winds slowly switch back
toward the SW and winds become weakly veering with height. This
looks to occur near or after 09z and thinking many locations will
bottom out by this time so should have negligible impacts on the
overnight lows. Otherwise, confidence is above normal that winds
will decrease with all guidance showing an eventual switch from
north to south which generally indicates a strong likelihood for
several hours of light and variable winds.

Afternoon readings on Tuesday will be similar to Monday or in the
upper teens to upper 20s. We should see increasing clouds as as
shortwave drops in from the north. Cannot rule out very light snow
showers but the dryness of our resident air mass will not allow
for full saturation so don`t expect much in the way of
accumulations outside a dusting to few tenths and possibly around
half an inch on the Camas Prairie. The system will bring an
reinforcing shot of cool, dry air in its wake and bump in
northerly winds. The bump in northern winds and cloud cover in the
south will keep temperatures a touch warmer for Tuesday night
with the exception of the sheltered mountain valleys across the
North Cascades and Okanogan Highlands where readings have the
potential to fall below zero again. /sb

Wednesday night through Monday: A cold and dry pattern is expected
to quickly transition to a more active potentially snowy pattern.

Wednesday night through Thursday night: Strong upper ridge
persists off the coast resulting in a continued cold and dry
northerly flow. A weak splitting wave may bring a few flurries or
brief light snow Wednesday night and Thursday.

Friday through Monday: The GFS, ECMWF, Canadian, and UKMET show an
active weather pattern with potentially two systems dropping into
the region from the northwest. There are model differences as
expected with the details with GEFS plumes showing a wide range of
potential snow amounts. However the GFS Ensemble mean POP`s, as
well as the ECMWF focus most of the action over Washington,
Oregon, and Idaho so confidence is moderate-high of an active
pattern. Given trajectory of systems from the northwest snow
levels should stay down to the valley floors for most towns. This
flow pattern (northwest) most favors the Cascade crest and Idaho
Panhandle for significant snow accumulations but latest model data
suggest significant snow amounts are also possible over Eastern
WA as milder Pacific air initially overruns the cold air in place
so stay tuned. The 12z GFS shows a more developed system with
stronger SW winds Friday night/Saturday compared to its Ensemble
Mean and other models so forecast favors the cooler ECMWF guidance
temperatures with less wind. Still some milder Pacific Ocean air
should come in Saturday with moderating temperatures but still
below normal through early next week. JW

&&

.AVIATION...
00Z TAFS: Some lingering VFR stratus associated with an exiting
inverted surface trough at the KPUW and KLWS and KCOE TAF sites
will dissipate between 02Z and 04Z tonight with largely clear but
very cold conditions at all TAF sites afterward. A storm system
sliding down the Pacific coast during the day Tuesday will miss
the forecast area with any precipitation...but high and mid level
clouds will thicken during the day. VFR conditions expected at all
TAF sites through 00Z Wednesday. /MJF

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane         1  23   7  26  13  26 /   0  10  10   0  10  10
Coeur d`Alene  -2  22   2  25  10  26 /   0  10  10   0  10  10
Pullman        -6  22   7  26  13  26 /   0   0  20  10   0  10
Lewiston       10  28  16  33  19  30 /  10   0  20  10  10  10
Colville       -4  23   4  27  12  29 /   0  20  10   0  10  10
Sandpoint      -2  21   4  25  12  25 /   0  20  10  10  10  20
Kellogg        -2  21   2  23  10  25 /   0  10  10  10  10  20
Moses Lake      6  32  15  34  19  35 /   0   0  10   0  10   0
Wenatchee      10  29  14  32  18  35 /   0  10  20   0  10  10
Omak            1  24   9  28  14  32 /   0  10  10   0  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$



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