Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 190015
AFDOTX

Area Forecast Discussion...Resent
National Weather Service Spokane WA
Issued by National Weather Service PENDLETON OR
414 PM PST Sat Nov 18 2017

...Significant snows possible Sunday night and Monday for the
mountains of the East Slopes North Cascades, Northeast Washington,
and North Idaho...

.SHORT TERM...Tonight through Sunday: Weak ridging allows for a
return of fog and low clouds in the usual locations, otherwise
the next storm system signals its approach with middle and high
clouds streaming in from the west that thicken and lower. Initial
pops and light qpf are painted over the Cascades and northern
mountains of Eastern Washington and North Idaho Sunday afternoon
generally to the north and west of a line drawn from Wenatchee to
Deer Park with the bulk of the precipitation expected to fall from
this storm system in the Sunday night/Monday time interval.

Sunday night through Monday...Low pressure system tapped into a
well maintained feed of subtropical moisture sags through Eastern
Washington and North Idaho. Some cold air trapped in the northern
valleys may initially be overrun by the warm southerly surge of
moisture associated with the system passage Sunday night into
Monday morning, but that will be the exception with remaining
locations having snow levels high enough in the 3-6 thousand foot
MSL range to limit heavy snow accumulation late Sunday and Sunday
night to the East Slopes of the North Cascades and Sunday night
into Monday for the mountains of North Idaho and some of the
northeast mountains of Eastern Washington with the expectation
that the weather system will take a northwest to southeast
oriented path of exit out of North Idaho. Snow totals between late
Sunday afternoon through early Monday would generally range from
6 to 10 inches at mainly 3500-4000 feet in the North Cascades.
This is marginal for a winter weather advisory for snow, thus
given the relatively thin layer of the highest snow totals, will
not issue an advisory at this time. Moderate to heavy snow is
also expected over extreme Northeast Washington and the Northern
Idaho Panhandle. Initially snow could fall as low as 3500-4000
feet over Northeast Washington and North Idaho but these levels
will steadily rise as the warm front nudges snow levels to around
5500 feet by midday Monday along the I90 corridor and points
south. By the time things wind down Sunday afternoon and evening
we could be looking at 5 to 10 inches of snow with the heaviest
amounts north of Sandpoint and Colville. These amounts are close
to winter storm warning criteria but we will wait on that for
another forecast or two since thats still a way out time wise. The
majority of the remaining non mountain locations will receive a
prolonged interval of rain from this passing system. With all the
warm air advection taking place as the wet weather system moves
through forecast temperatures will be on the warm side of what
would be considered normal for this time of year.

&&

.LONG TERM...Monday night through Saturday: A well maintained plume
of subtropical moisture sandwiched between a large area of low
pressure off the coast and inland ridging sets up the stage for
low pressure systems to utilize the efficient moisture source as
they pass through Eastern Washington and Northern Idaho with a
warm south to north trajectory of approach/exit. What appears to
be a wet warm front moves through the region Monday night into
Tuesday with the warm sector moving very slowly eastward. So slow
in fact that continued rainfall associated with high snow levels
running generally between seven to ten thousand feet mean sea
level are coupled with the warmest temperatures of the seven day
forecast from Tuesday night through Thursday. The rain and the
resulting mountain runoff will result in higher streamflow
Wednesday and Thursday but since there is enough snow in the
mountains to absorb a significant quantity of the runoff it should
only result in a slight bump in streamflow increase with no
mainstem river flooding anticipated. The backside of what is left
of the baroclinic band/moisture plume passes through as a cold
front Thursday night and allows for a change of air mass to a
cold conditionally unstable one on the north side of the jet
stream Friday and Saturday. This allows for most lowland locations
to see a return of colder but drier weather with any pops limited
to the higher terrain within close proximity of the lee of the
Washington Cascades and portions of the North Idaho Panhandle.

&&

.AVIATION...00Z TAFs: A flat ridge will persist through Sunday
with abundant mid and high level clouds passing through the
region. dc


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        30  44  36  45  35  45 /   0  10  90  30  60  80
Coeur d`Alene  31  43  35  42  34  44 /   0  10  90  50  50  80
Pullman        33  47  36  46  38  49 /   0  10 100  70  60  80
Lewiston       32  50  40  51  40  53 /   0   0  80  70  50  70
Colville       28  40  33  42  32  41 /   0  30  90  30  40  80
Sandpoint      28  41  34  39  30  42 /   0  10 100  60  50  90
Kellogg        27  42  32  39  34  41 /   0  10 100  80  60  80
Moses Lake     29  47  35  49  31  46 /   0  10  60  10  30  80
Wenatchee      31  44  33  46  33  43 /   0  20  60  10  30  80
Omak           30  40  31  43  33  43 /  10  30  60  10  20  70

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$


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