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Area forecast discussion 
National Weather Service Spokane Washington
450 PM PDT Fri Oct 21 2016

showers will continue through tonight, then begin to exit to the
east through the morning on Saturday. Clearing skies Saturday
morning will give way to more fog and low clouds across the basin
and into the mountain valleys. Drier weather is expected for many
locations on Saturday into early Sunday but the next weather
system is expected to move push a threat of rain into the Cascades
late in the day and across the remainder of the area late Monday
or Tuesday. Wet and unsettled weather will then continue through
most of the week.


tonight: there are two synoptic level features of note for tonight.
The first is a stalled frontal boundary extending from southwest
or to western Montana. Precipitation will continue to fall along this
boundary, which will primarily be focused across southeast Washington into
the central Panhandle mtns this evening. The second feature of
note is an upper level shortwave trough that is currently rounding
the base of the upper level low in the Gulf of Alaska. The leading
edge of this shortwave has produced heavier showers with embedded
thunderstorms along the Washington coast. The upper level disturbance will
act to displace the stalled frontal boundary to the southeast with
time overnight. It will also act to enhance precipitation as well
with models showing a better chance for more moderate precipitation
amounts. Locations southeast of a line from Pullman to Lookout
Pass are expected to see between a quarter an inch up to a half
an inch of precipitation. Models are also showing some mid level
instability associated with the upper level wave across much of
eastern Washington. The NAM is the most aggressive with showers blossoming
over the northern basin and up into the Okanogan Highlands to the
northern Panhandle. The GFS is also supportive of showers over
these area, but is not quite as wet. Mid level cloud cover starts
to clear the area from west to east late tonight. I added patchy
fog in the Cascade valleys, across the basin and up into the
northern mtn valleys. /Svh

Saturday through monday: overall there will be a drying trend for
Saturday but it will be slow to come in northeast Washington and
the north Idaho Panhandle as lingering moisture in this area is
expected to produce rain shower activity until early afternoon.
Morning fog is anticipated to stretch into the east and south
Central Basin as well as the Cascade and Snake River valleys but
should lift later in the morning hours.

A short lived high pressure ridge responsible for the modest
drying into Saturday evening will give way to frontal band
precipitation approaching the Cascades early Sunday morning. An
upper level trough will dig off the West Coast and slow the
front's progression but but the Cascade area will be subject to
the best chance of rain with very high elevation snow above 5500
feet. Lighter stratiform rain will be possible in the warm sector
ahead of the front in the northern mountains of Washington into
Sunday night.

The low pressure system off the coast will be the driver of
weather into Monday as well but the front makes little headway
inland. So the best chances of rain will still near the Cascades
and mainly isolated showers elsewhere as moisture tracks up from
the south. Overall rain totals near the Cascade crest could be up
to a half inch during this period with only light amounts less
than a tenth of an inch elsewhere. Tc

Monday night through friday: a broad area of low pressure residing
along the wrn US coast will influence the weather pattern through
the period. Several rounds of precipitation are expected to impact
the inland northwest...some which may be moderate to heavy around
midweek. Medium range models are in general agreement of the
longwave pattern setting up however details related to embedded
shortwaves and timing of the heaviest precipitation are far from
certain with large model spread noted. It does appear that the low
will remain fixed off the coast keeping the inland northwest in a mild
south/southwest flow suggesting precipitation will largely be in
the form of rain except the highest peaks. Moisture parameters
also indicate a reasonable threat for another rich fetch of
subtropical moisture impacting the region around the Wednesday
time-frame. Consequently, with little to no dry air intrusion
expected through the weekend... grounds will remain saturated with
additional rain arriving...and locations in steep terrain
susceptible to rock and land slides should remain vigilant.

The first round of rain will accompany a shortwave slinging
around the offshore flow Monday night and Tuesday. Rainfall
amounts with this feature could be up to a half an inch but most
locations will generally be in the 0.10-0.25" range. Precipitable
water values accompanying the wave will be upwards of 0.70",
roughly 1 Standard deviation of normal. In the wake of this
wave...a more appreciable fetch of subtropical moisture gets drawn
northward ahead of the offshore low bringing yet the potential for
another widespread rain event. The trajectory of this moisture
plume differs from the last two atmospheric rivers which came in
with more a west or southwest punch directly off the Pacific. In
this event...the fetch takes on more of a south to north
trajectory around a deep offshore low so conceivably, it should
yield far less precipitation for the Cascade crest and westward
facing slopes...and potentially more for the southern aspects
including the northern mountains. However...with any deep fetch of
subtropical moisture...lift associated with terrain is just one
component and whether a frontal boundary stalls and/or duration
will also play key roles. The pattern will favor mild temperatures
with the largest departures likely to accompany overnight lows.
For example, ensembles suggest Spokane will not hit the freezing
mark through the next 7 days. /Sb


00z tafs: a boundary stalled near southeast Washington/lower Idaho and a
shortwave moving in from the west will provide a threat of showers
around most taf sites tonight into early Saturday. The
precipitation threat will be steadier/more focus toward puw/lws
near the stalled boundary and the rain may be moderate to locally
heavy. More isolated to scattered showers will threaten the other
taf sites. A moist boundary layer will provide isolated MVFR/IFR
conditions early this evening...becoming more widespread later
this evening, overnight into early Saturday...with the potential
for fog. Conditions will then improve at most locations after
15-19z as weak high pressure moves in. /J. Cote'


Preliminary point temps/pops...
Spokane 41 53 40 55 45 58 / 20 20 10 10 10 20
Coeur D'Alene 43 52 41 56 44 58 / 30 30 10 10 20 20
Pullman 43 54 43 58 46 62 / 90 10 10 10 10 10
Lewiston 46 60 46 62 48 65 / 90 10 10 10 10 10
Colville 38 52 37 54 41 56 / 40 10 10 20 30 40
Sandpoint 39 49 37 53 40 55 / 40 30 10 20 30 20
Kellogg 41 48 40 55 42 57 / 70 40 10 10 10 20
Moses Lake 39 58 41 57 43 58 / 10 0 10 10 10 20
Wenatchee 41 57 43 55 43 55 / 30 0 10 30 20 40
Omak 38 56 40 55 42 55 / 30 0 10 20 30 50


Otx watches/warnings/advisories...


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