Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 091012

Area Forecast Discussion
National Weather Service Spokane WA
212 AM PST Mon Dec 9 2019

Dry weather is expected for today and Tuesday under a ridge of
high pressure, although low clouds and patchy freezing fog will
return. A weak weather disturbance arrives Tuesday night into
Wednesday, followed by wetter and unsettled conditions for
Thursday into Friday.


Today through Tuesday...A sharp upper level ridge exists over the
coastal northwest this morning with dry northerly flow aloft. This
rideg is promoting a subsidence inversion to form over the
forecast area. This inversion aloft combined with the normal
nocturnal inversion and short daylight period this time of year
will bring stagnant conditions with low level stratus and at least
patchy morning and overnight freezing fog and afternoon simple
fog to much of the basin and valleys branching off of the basin
for the next two days. Clear to partly cloudy conditions will
prevail above this inversion on the high terrain around the
region. There is little else to expound upon during this period
with overnight low temperatures near normal for this time of year
and daytime highs still running normal a bit above normal but
dependent on low confidence forecasts of relative clearing during
the afternoon hours at any particular location. Best chance for
valley/basin clearing will be the Palouse and L-C valleys
benefiting from weak gradient downslope while the deep
basin/Cascades lee areas where the gradient will pool the moist
boundary layer air will be slowest to clear if at all.

Tuesday night and Wednesday...The next storm system will climb
over the rideg and crush it temporarily as a transient short wave
Tuesday night before the rideg rebounds on Wednesday.
Deterministic and ensemble models are in poor agreement regarding
the moisture feed and precipitation potential with this quick
hitting wave. The GFS is wetter and stronger while the ECMWF is
weaker with less favorable moisture. The National Blend Model
seems to be siding with the weaker EC, but does suggest a moderate
chance of overnight and early morning snow potential over most of
the region...although amounting to little more than a trace to
1/2 inch accumulation on the basin and valley floors with perhaps
an inch or two in the Idaho mountains and near the Cascade crest. we have seen recently even a small amount of snow on
frozen road surfaces could cause hazardous conditions and so the
Wednesday morning commute period may be slippery around the region
despite relatively low snow accumulation potential.

On Wednesday the wave will pass off to the east with lingering
snow showers upsloping into the panhandle and a return to fog and
low clouds for the rest of the area as the upper rideg rebuilds.

Wednesday Night through Sunday: A closed low moving into the Gulf
of Alaska will flatten the ridge and send numerous weather
disturbances into the Pac NW starting Wed night. The strongest
system looks to move in Wed night through Thur night. EC
Ensemble shows fairly high probabilities of more than a half an
inch of qpf for the Cascades, extreme eastern WA and north ID. GFS
shows it as well, but not as high probability. Looks like we will
have a good opportunity to receive some much needed snowfall in
our mountains. The Cascades could see up to a foot, with much higher
amounts along the crest. The ID Panhandle mtns could see up to a
foot as well.

Periods of mountain snow and valley rain or snow is expected. We
start out fairly warm wed-fri with highs in the upper 30s to low
40s and our lows in the upper 20s to around freezing. This will
keep the valley precip as a rain or rain/snow mix for the most
part. Any snow in the valleys would be short-lived and very
light. By saturday however it looks like we transition from
westerly flow to a more northwesterly flow, which will bring in
some slightly cooler temps. This will allow us to see a better
chance of snow to the valley floors, though by this time the
ensembles suggest that most precip may be mostly confined to the
Id Panhandle and Cascade crest. /Nisbet


06Z TAFS: Flow has become more southerly and is allowing
low level moisture to return overnight allowing for freezing
fog and low cloud development producing IFR/LIFR ceilings and
visibilities that may show some improvement mostly likely
after 21Z Monday. /Pelatti


Spokane        34  28  36  31  38  33 /   0   0   0  30   0  80
Coeur d`Alene  36  30  40  32  39  34 /   0   0   0  30  10  80
Pullman        38  29  41  32  42  35 /   0   0   0  30  10  80
Lewiston       44  31  44  36  46  38 /   0   0   0  30  10  70
Colville       37  23  37  27  38  31 /   0   0   0  20  10  80
Sandpoint      35  29  36  32  37  33 /   0   0   0  40  10  90
Kellogg        36  31  39  33  39  35 /  10   0   0  50  30  80
Moses Lake     36  27  36  28  39  31 /   0   0  10  20  10  60
Wenatchee      36  28  36  29  38  31 /   0   0  20  20  20  70
Omak           37  26  34  29  36  32 /   0   0   0  20  10  60




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