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Area forecast discussion 
National Weather Service Spokane Washington
217 am PDT Sat Nov 1 2014

Synopsis...
a slow moving frontal system will pass through the region over
the next 24 hours. Light rain will develop over far eastern
Washington and the Idaho Panhandle today. Sunday will be a break
period followed by a very moist period on Monday through
Wednesday featuring valley rain and High Mountain snow.

&&

Discussion...
today and tonight...a deep and highly meridional upper level
trough with axis just off the Pacific coast will drift onshore
today. The forecast area will be under a deep and moist southerly
flow regime ahead of this trough axis. The main trough base
dynamic region will eject into the Great Basin and then hook north
into Idaho and promoting surface cyclogenesis over Idaho and
eventually Montana tonight.

The forecast area will be on the edge of the strong dynamic
forcing featuring differential vorticity advection and mutually
supporting jet divergent regions which will drive the
cyclogenesis. The eastern half of the forecast area will be
impacted by this forcing and fueled by deep moisture. Radar is
already filling in with moderate rain returns from Walla Walla to
Sandpoint and points east early this morning. The situation will
continue to deteriorate further as the day wears on over these
regions...while the western zones will be Manly dry but with thick
mid and high clouds for minimal sunshine. Expect a generally wet
day featuring intermittent light rain and High Mountain snow over
the Idaho Panhandle and extreme eastern Washington with 1/3 to 1/2
inch of rain possible with near 1 inch of precipitation in the
mountains. The southerly flow will keep snow levels up around
5000 feet today.

Tonight the trough axis will cross the region and allow snow
levels to begin lowering. The lingering precipitation over the
Idaho Panhandle will become snow above 4000-4500 feet with
accumulations possibly reaching early season warning criteria over
the high terrain...and the current Winter Storm Watch for the
Shoshone County mountains above 4500 feet will continue with the
morning forecast package. /Fugazzi

Sunday: precipitation wrapping around the backside of an area of low
pressure over Montana will rapidly decrease in intensity and wane
through the morning and early afternoon as the storm system shifts
into the northern plains. A mid-level dry slot will shift into
Idaho leading to rapid drying of the dendritic layer and despite
the continued upsloping flow and saturated lower levels,
precipitation intensity will become light trending from a mix of
light mountain snow and valley to rain toward a combination of
drizzle and flurries. Snow levels will range between 3800-4000
feet Sunday morning rising near 4500 feet by the late afternoon.
Any chance for accumulating snows will likely have to come during
the early morning hours when precipitation intensity will be
greatest. The remainder of central and ern Washington will generally
remain dry with areas of morning fog and stratus giving way to
increasing clouds as the next weather system approaches.

Sunday night through saturday: the Gulf of Alaska low will dig into
the ern pac and direct an atmospheric river at the northwestern
US. This will bring several rounds of precipitation, gusty winds,
and mild temperatures. Sunday night and Monday will be initial
influx of atmospheric moisture and be accompanied by modest
westerly flow. This will equate to thickening clouds with spotty
light precipitation and quantitative precipitation forecast amounts generally less than a tenth of
an inch. The exception will be along the immediate Cascade crest
where upwards of a quarter or more will be possible through Monday
evening. Snow levels across the northern mountains will start off
just shy of 4000 feet Monday morning suggesting any light
precipitation before midday could result in a period of light snow
on Sherman Pass.

Precipitation will increase in coverage and intensity Monday night and
Tuesday as subtropical moisture continues to flood inland and a
weak frontal system skirts to the northwest. Widespread quantitative precipitation forecast
amounts between a tenth and quarter of an inch will be found
across the basin (less in the Lee of the Cascades and more eastern
basin with the valleys of NE Washington and nrn Idaho looking at closer to
amounts between a quarter and half an inch. The Cascade crest will
receive over an inch of liquid while the mountains of NE
Washington and nrn Idaho should look to receive between 0.75 -
1.00" with local amounts likely to exceed an inch. Snow levels
will start off lowest Monday night and continue to climb as the
subtropical moisture pours inland. Levels across the northern and
eastern mountains will start off 5500-6000 feet increasing 7500
feet by Tuesday evening. In the Cascades, snow levels bounce
between 7000-8000 feet and 7000-9000 feet closer to the blue mtns.

The passing frontal system will briefly suppress the axis of subtropical
moisture toward northern Oregon Tuesday night with westerly flow
bringing drying in the Lee of the Cascades, Okanogan Valley, and
Okanogan Highlands. Numerous showers will continue across the
Cascade crest and mountains east of the basin as winds within the
850-700mb layer blow 25-40kts out of the W/SW.

For the middle to end of the week (wednesday - saturday), there
is increasing confidence that a longwave trof between 150-160w
will begin to swing east and in return...pump heights over the
western US. The axis of deeper moisture near the Washington/or border will
respond by lifting north ahead of a developing warm front and
looks to retreat toward the international border during the
Wednesday time-frame. How far north the shield of precipitation
retreats carries moderate uncertainty. The trof will continue to
swing east and eventually swing inland somewhere in the Thursday -
Friday time-frame. Ec and GFS appear to have flip-flopped
solutions when compared to 24 hours ago and also differ in timing
by nearly 24 hours. Now the ec shows less offshore splitting of
the 500mb trof and a stronger cold front passage coupled with a
windy scenario. The GFS also supports windy conditions but the
system is weaker and 12-24 hours slower. All things considered,
the upcoming frontal system will bring a good chance for windy
conditions, enhance precipitation, and cool temperatures down some
but we have very little confidence regarding timing and when/where
to place the highest pops each 12 hour period given these
uncertainties.

Outside the late week storm system, Tuesday will be the breeziest
day of the week with breezy southerly winds somewhere in the 10
to 20 mph range. All other days will generally be around 10 mph or
less except for the mountains. The subtropical origins of the
incoming air mass will also deliver above normal warmth with mild
overnight lows and potential for several days of 60's across the
Lower Basin. /Sb&&

Aviation...
06z tafs: very slow eastward moving front continues to keep some
precipitation over the aviation area. Abundant low level moisture
from the recent rainfall keeps fog and stratus in some shape or
form overnight and morning hours in addition to the lower stratus
associated with precipitation along the front. /Pelatti

&&

Preliminary point temps/pops...
Spokane 50 34 47 36 48 43 / 80 20 10 20 50 80
Coeur D'Alene 49 36 46 34 47 41 / 100 60 10 10 60 80
Pullman 49 34 47 36 50 44 / 100 70 10 20 40 70
Lewiston 54 38 53 38 54 46 / 100 70 10 10 30 50
Colville 51 33 49 34 47 42 / 20 10 0 20 60 100
Sandpoint 48 36 45 32 45 40 / 90 60 10 20 70 90
Kellogg 46 37 43 33 44 39 / 100 100 40 10 60 80
Moses Lake 55 36 53 40 52 48 / 10 0 0 20 30 60
Wenatchee 56 37 54 41 51 46 / 0 0 10 40 30 60
Omak 52 33 50 36 49 43 / 10 0 0 30 40 70

&&

Otx watches/warnings/advisories...
Idaho...Winter Storm Watch from this afternoon through Sunday afternoon
for central Panhandle mountains.

Washington...none.
&&

$$

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