Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 292346

Area Forecast Discussion
National Weather Service Spokane WA
346 PM PST SUN NOV 29 2015

Low clouds and areas of fog will be common in valleys. Strong
high pressure will contribute to air stagnation and cloudy skies
in the lowlands through Tuesday. A frontal system is expected to
bring a chance of wintry precipitation Tuesday night into
Wednesday...with more unsettled weather through the rest of the



Tonight and Monday...Blocking ridge of high pressure continues to
keep strong subsidence inversion over Eastern Washington and
Northern Idaho. The resulting poor mixing and ventilation will
allow for continued low clouds and fog in valleys and lowlands
while the mountains above 4000 feet MSL remain generally clear and
cloud free. Below freezing temperatures persist under the fog and
low clouds which is allowing for patchy ice to accumulate at
times. This patchy ice combined with sudden reduction in
visibility brought about by patchy fog has resulted in less than
optimal driving conditions. Have utilized other tools via social
networking to address this issue. Additionally some very light
snow flurries have occasionally fallen from the low stratus so
have included their mention in the forecast for tonight and
tomorrow for many locations affected by the low clouds. /Pelatti


Monday night through Wednesday morning: A pair of upper level
disturbances will push into the Inland Northwest and flatten out
the upper level ridge of higher pressure. The first, expected for
Monday night and Tuesday, will shear apart and have very little
impact at the surface. We will still be dealing with a large
amount of stratus cover. The passing upper level wave may provide
just enough moisture aloft to produce some flurries out of the low
stratus. The NAM is placing very light precip across the east
slopes of the northern Cascades and out into the Okanogan
Vly/Highlands and Waterville Plateau. Weak easterly winds will
result in just a little bit of lift that should also increase the
chances for some flurries across the lower elevations.

The Air Stagnation Advisory has been extended through Tuesday
evening. Confidence is high that little will change through this
point. Ventilation will continue to remain poor with inversions
remaining strong. Slight improvement will be possible Tuesday
night across in the Central Panhandle, across the Palouse and
down in the L-C Valley as a southeast pressure gradient
strengthens slightly. These look to be the first areas that will
see some improvement after this time; however, most other
locations may not see much improvement even with some precip
moving in overnight Tuesday.

The second disturbance will for Tuesday night will be a little bit
stronger. The bulk of the dynamics will miss us to the north, so
not much mechanical mixing is anticipated. The lack of mixing is
what is anticipated to be problematic. The reason is the we will
have a warm tongue pushing up across the Columbia Basin. This
warmer air will result in a melting layer while temperatures will
likely remain at or below freezing for much of the basin. Best
chances for temperatures to warm up above freezing will be across
the far southeast portion of the forecast area and down into the
L-C Valley where downsloping could be a factor. Still, even these
locations may see a little bit of freezing rain through Wednesday
morning. Confidence is higher for a wintry mix across the western
basin and into the Wenatchee Area. Precip type is expected to
remain as snow across the northern valleys and likely across the
Spokane/Coeur d`Alene Corridor as well. ALthough precip will be
light, roadways may be slick across much of the region due to the
snow and freezing precip.

Wednesday afternoon through Sunday: Confidence is low for this
part of the forecast. There is more model variability with the
timing of subsequent disturbances. The general trend will be for a
continued moderation of the air mass. A wintry mix will be
possible for the northern portions of the region and up against
the east slopes of the northern Cascades through at least Thursday
morning. A cold front looks to sweep through after this time.
This will result in the possibility for some breezy conditions
through Friday afternoon. This weather system for later in the
week will increase snow levels, but the mountains will see the
possibility for moderate snow accumulations with impacts to passes
expected. /SVH


00Z TAFS: A strong inversion will remain over the Columbia Basin
through 00Z Tuesday with no weather systems expected to impact or
weaken it. A field of stratus with tops around 4Kft will remain
over all TAF sites through 00Z Tuesday. There is high confidence of
widespread IFR and LIFR ceilings and visibilities at all TAF
sites except KLWS where MVFR ceilings will prevail with IFR
conditions during the overnight and early morning hours. /MJF


Spokane        15  28  17  29  25  34 /  10  10   0  10  30  60
Coeur d`Alene  12  29  17  31  26  35 /   0   0   0   0  20  60
Pullman        18  29  18  35  28  38 /  10  10   0  10  20  50
Lewiston       20  30  21  36  29  40 /  10  10   0  10  10  40
Colville       13  30  17  32  24  32 /  10  10   0  10  30  60
Sandpoint      14  30  17  32  23  33 /   0  10   0   0  20  60
Kellogg        14  30  16  32  24  35 /   0   0   0   0  10  60
Moses Lake     15  28  18  29  27  34 /  10  10  10  10  50  20
Wenatchee      17  28  19  26  25  32 /  10  10  10  10  60  30
Omak           15  28  17  25  24  32 /  10  10  10  10  60  20


ID...Air Stagnation Advisory until 4 AM PST Wednesday for Central
     Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis
     and Southern Nez Perce Counties-Lewiston Area-Northern

WA...Air Stagnation Advisory until 4 AM PST Wednesday for East Slopes
     Northern Cascades-Lower Garfield and Asotin Counties-Moses
     Lake Area-Northeast Blue Mountains-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley-Spokane Area-Upper
     Columbia Basin-Washington Palouse-Waterville Plateau-
     Wenatchee Area.


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