Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 170920

Area Forecast Discussion
National Weather Service Spokane WA
220 AM PDT Thu Oct 17 2019

Several rounds of rain, mountain snow, and breezy winds
are expected through the next 7 days.  Seasonal temperatures
for the rest of the work week will trend cooler than normal
by the weekend.


Thursday and Friday: An unsettled pattern continues as the first
in a series of disturbances wets down the northern Idaho
Panhandle this morning. The next wave will move into the Columbia
Basin, Palouse, and north into the Spokane area Thursday evening
spreading low elevation rain and mountain snow as it most across
the Inland Northwest. Precipitation will begin to taper off
Friday morning and become more showery through the remainder of
the day. Snow levels will range from 4500-5000ft this morning
through today, but begin to drop Friday morning to nearly 3000ft
across the Cascades before rising to 4000-4500ft through the day
Friday. Although rainfall amounts will mostly be on the light side
less than a tenth of an inch across most areas, higher elevations
across the Cascades may see two to three inches of precipitation
across the crest Thursday through Friday morning. This could
equate to a couple feet of new snow across the highest ridges. The
northern Panhandle mountain locations may see much less precip
amounts ranging only between .10 to .20 inches or two to four
inches of new snow across higher peaks. The typically breezy areas
of central and eastern Washington and the Idaho Palouse will
experience west or southwest winds of 15 to 20 mph with gusts to
30 mph on Thursday and again on Friday across the southern
Palouse. These gusty conditions should continue through at least
the weekend. /aky

Friday night and Saturday: Moderate to heavy precipitation is likely
to impact the Inland NW during this time-frame courtesy of deep
low dropping through the region from the northwest. Ample mid and
upper-level ascent along the left exit region of a 165kt jet and
shortwave dynamics will allow a surface low to retain its
intensity between 997-1001mb while traversing the interior. This
is not usually the case; Typically these systems fill and weaken
while crossing the Cascades. As such, the strong lift coupled with
sufficient moisture (PWATS ~ 0.50") will result in widespread
precipitation with bands of moderate to heavy intensities. The
track of the surface low will be key to which areas receive the
heaviest precipitation and models continue to waver within a few
counties regarding these details.

For the lower elevations, this will largely be a cold rain with
temperatures in the upper 30s to mid 40s. There is some concern
however, that under the heaviest precipitation bands north and
east of the low, snow levels may get driven down toward 2500-3000
feet. Potential impacts within this band would be a quick 1-3
inches of heavy wet snow which could lead to localized tree damage
and/or power outages. Confidence is not very high exactly where
this band sets up or if the snow would have similar damaging
impacts to deciduous trees that we saw with a system on October
9th around Spokane and Rathdrum. The setup is a bit different as
is time of day. Intensities of the snow will be worth closely
monitoring. Confidence is higher that snow will fall in the higher
elevations and likely to bring wintry driving conditions to the
mountain passes. Attm, Lookout and Washington Passes carry the
greatest risk for significant snows. Sherman Pass will see snow,
but amounts are far less certain.

Rainfall amounts in the lowlands will range from a tenth in the
lee of the Cascades to near an inch under the aforementioned
heavier bands. Minor urbanized flooding will be possible under
these heavier bands where proper drainage could be impacted by
fall leaves. Flashy creeks like Paradise near Moscow, ID could
also see sharp rises. Gusty winds westerly winds will be found
south of the low. Speeds of 10-20 mph with gusts between 30-40 mph
will be possible from Wenatchee to Ritzville to Lewiston.

The main precipitation threat with this system will slowly
expand into the region Friday night into Saturday morning, bands
of moderate to heavy precipitation develop with the passing
surface low through much of the day Saturday then look for
precipitation to slowly wind down and exit Saturday evening/night.

Sunday through Thursday: A warm front lifts through the region
Sunday as high pressure builds in from the Pacific.  The warm
front will lead to scattered light showers but amounts will be
light and generally under a quarter of an inch. Snow levels will
start off around 4000 feet and steadily rise toward 5000-6000
feet. A second warm front arrives Monday and ushers a deep plume
of subtropical moisture into the region. This pushes snow levels
above 6000 feet and all mountain passes. On Monday, light, steady
precipitation mainly in the form of rain and high elevation snow
will persist over the windward slopes of the Cascades and Idaho
Panhandle with drier weather in the lee of the Cascades. Another
deep low pressure system drops in the from the northwest Tuesday
and will track along the subtropical moisture plume bringing
another threat for moderate to heavy precipitation. This will be a
warmer system with snow levels near 7000 feet. Breezy but low
impact winds will be around Sunday through Tuesday. Stronger wind
speeds will be possible with the passage of the next low on
Wednesday. Details will likely change with this latter system so
stay tuned. /sb


06Z TAFS: Lowering cigs and widespread rain is moving across E WA.
Periods of LIFR/IFR conditions are possible during the AM hours
of 10Z-16Z as lower cigs and vis develop with heavier bands of
precip for GEG-SFF-COE. MVFR cigs possible for PUW with -ra band
overnight. Winds will increase aft 16Z and be breezy at times
through the aftn and evening for GEG-SFF-PUW-MWH.


Spokane        55  39  52  38  44  32 /  20  60  30  60 100  40
Coeur d`Alene  53  39  52  38  41  34 /  40  90  40  70 100  60
Pullman        54  38  52  37  42  34 /  30  80  20  60 100  70
Lewiston       61  46  62  45  51  41 /  50  60  20  50 100  60
Colville       59  34  56  33  47  27 /  30  60  30  60 100  20
Sandpoint      52  39  52  38  42  35 /  60  90  60  80 100  70
Kellogg        51  39  48  39  39  36 /  90 100  70  80 100  80
Moses Lake     62  38  60  39  54  34 /  10  50  10  70  70  10
Wenatchee      58  42  55  41  50  38 /  30  70  30  80  80  10
Omak           57  37  55  38  48  33 /  20  70  30  60  80  10




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