Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 311250

Area Forecast Discussion
National Weather Service Spokane WA
450 AM PST SAT JAN 31 2015

Today will be another cloudy and chilly day in the Inland
Northwest. A frontal system will bring light snow to much of the
region on Sunday. Another front is expected on Monday, and it
should bring rain and mountain snow. Thursday and Friday also look
quite rainy next week.



...Light Snow Accumulations Likely Sunday...

Today: A quick moving Clipper-type system will dive into Montana
this morning. This system influenced our weather overnight causing
the fog layer to lift a bit over north Idaho and eastern
Washington. It provided just enough mid level cooling to bump our
inversion layer up several hundred feet. The subtle lifting of the
fog/stratus layer coupled with some southerly low level upslope
flow produced light snow/flurries over the West Plains and
portions of north Idaho. As the Clipper moves southeastward this
morning, the boundary layer flow will transition from
south/southwest to a more north/northwest. This low level flow
regime generally favors precipitation over southern Shoshone
county, the Camas Prairie, and Palouse. By afternoon, the
influence of the Clipper will probably diminish as it moves toward
Wyoming. It is doubtful that the deep and widespread stratus deck
will break up much this afternoon. Last evening`s sounding from
Spokane showed the status deck to be about 2000 feet
thick...probably too formidable to be broken by today`s Clipper.

Tonight and Sunday: Our resident upper level ridge will be
flattened on Sunday by a moist frontal system. This front will be
shoved in our direction by a large upper low anchored over the
Gulf of Alaska. The center of this upper low won`t move much as it
sends this shearing frontal system our way. Without much upper
level support, the surface features with Sunday`s system aren`t
particularly impressive. What this system lacks in strong synoptic
forcing, it makes up with moisture. The subtropical origins of
this front should produce widespread light snow from the East
Slopes to northeast Washington to north Idaho. The relatively weak
wind fields actually look to limit mixing with this system which
should keep temperatures cold enough to support snow Sunday
afternoon and evening over most of the central and northern Idaho
Panhandle and most of northeast Washington. Valley locations like
Colville, Sandpoint, Spokane, Kellogg will have a good shot at an
inch or two of snow. Pavement temperatures Sunday afternoon could
be marginal for significant road accumulations. If the bulk of the
snow arrives toward evening, the chance for slick driving
conditions will be heightened. Snow intensities also play a big
role in how efficiently snow accumulates. With the "big game"
Sunday afternoon, motorists may experience winter driving
conditions to and from parties. /GKoch

Monday through Wednesday night...Longwave ridge positioning over
the Pacific Northwest allows for continued warm trajectory of
approach from southwest to northeast. Initially there is a brief
break in systems early Monday but another system riding up the
same southwest to northeast tap of moisture that feed the Sunday
system spreads more precipitation, mostly in the form of rain with
fairly high snow levels, Monday and Monday evening. Monday night
the system looks to have made an exit into Northwest Montana with
the trailing moisture feed translated to the south passing over
Oregon instead of Washington. Indeed there may be what looks to be
a bit of a cold front at around that time that drops down from the
north Tuesday. It looks to impact snow levels and temperatures
mainly up near the Southern British Columbia Border Tuesday and
Wednesday but it is rather weak and doesn`t make much, if any,
dent in the lingering ridge of high pressure in the area. There is
a brief break between systems Wednesday night with the exit of the
cold front before more weather systems with warm southwest to
northeast trajectories of approach bring more wet weather, rather
high snow levels, and mild temperatures to the region.
Additionally after Tuesday with all this moisture available,
generally light surface winds, and general high pressure it
doesn`t seem unreasonable to expect any areas lacking
precipitation during the overnight hours to have fog and/or low
clouds reappear, and with them perhaps drizzle and/or flurries to
fall out of it at times as well. /Pelatti

Thursday through Friday Night: Activity level picks up once again
as a series of systems are slated to pass through the region late
in the week. While models have slight differences with precise
timing and subtle details, they agree on an increasingly warm and
wet pattern for the later part of the work week. Multiple warm
fronts supplied with a warm subtropical moisture feed will once
again bring widespread precipitation to the region. The first
round comes Thursday into Friday with the first warm frontal
passage. Thursday into Thursday Night appears to be the most
complex period as the transition of precip type for the northern
and Cascade valleys takes place. Enough cold air remains to
support snow Thursday before the warmer flow intrudes overnight.
By Thursday night warmer air overruns the colder in the far
northern valleys to promote a potential period of freezing rain.
By Friday the next surge of warm air will end the chance for mixed
precip in the valleys with snow levels rising to over 7000ft in
the south and near 6000 for much of the north. This will even
transition many mountain locations to rain by Friday and into
Friday night.

Late in the period we see mild southerly winds pick up allowing
for much better warm air advection. Temperatures rise to above
normal levels with highs reaching the upper 30s and 40s for most
by Friday while overnight lows sit above the freezing mark for the
vast majority. Overall the period looks to simply add insult to
injury as we continue to struggle in building any notable mountain
snow-pack this winter. /Fliehman


12Z TAFS: Light snow or flurries should be on the decrease by 15z
around Spokane and Coeur D`Alene as low pressure system dives into
Montana and Wyoming by this afternoon. Flurries or drizzle may
persist in Pullman and the southern Idaho Panhandle until 19z-21z.
With the upper level ridge rebounding this afternoon following the
passage of the Montana system, look for the stratus deck to
persist through the TAF period. The inversion layer may lift and
drop today and tonight causing ceilings to rise and lower. In
general, ceilings at most sites are expected to be in the
800-2000 ft range. /GKoch


Spokane        34  29  34  32  37  32 /  10  10  70  40  80  50
Coeur d`Alene  34  28  34  32  38  34 /  10  10  90  60  90  60
Pullman        37  32  40  36  44  37 /  10  10  50  60  90  60
Lewiston       43  33  44  37  48  39 /  10  10  40  40  70  50
Colville       36  28  34  30  34  31 /  10  10  90  40  60  40
Sandpoint      34  26  33  30  35  32 /  20  10  90  70  90  60
Kellogg        37  27  35  33  37  34 /  20  10  90  80  90  90
Moses Lake     39  31  39  31  41  35 /   0  10  30  20  50  20
Wenatchee      38  31  39  32  40  34 /   0  30  40  20  40  20
Omak           37  31  34  30  35  31 /   0  30  60  20  40  20



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