Area Forecast Discussion
Issued by NWS Spokane, WA

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846
FXUS66 KOTX 132218
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
218 PM PST Fri Dec 13 2019

.SYNOPSIS...
Snow showers are expected through the weekend mainly over the
mountains. Light to moderate snow accumulations will be possible
over southeast Washington and the Camas Prairie tonight. Monday
and Tuesday are likely to be dry with a return to unsettled
weather possible for the middle to end of next week.

&&

.DISCUSSION...

Tonight through Saturday: With the jet stream oriented into
northern California, the Inland Northwest finds itself in unstable
west to northwest flow. Much of the shower activity has remained
over the Cascade crest and into the Idaho Panhandle in the absence
of mesoscale forcing mechanisms in the atmosphere. Showers are
primarily being forced by orographics over the higher terrain.
However, focusing attention offshore at 128W/46N, we can depict a
weak shortwave trough of lower pressure approaching in satellite
imagery. This wave will push across eastern Washington overnight.
Downsloping off of the Cascades will limit shower development in
the lee of the mountain range, but favorable upslope flow across
southeast Washington and into the southern to central Idaho
Panhandle will result in a redevelopment of precipitation.
Temperatures up at 850 mbs will continue to cool to between 3 to 4
below Celsius, which will be cold enough for snow at all
elevations except a rain/snow mix in the Lewiston/Clarkston
Valley. Heaviest snow amounts will be over the Central Panhandle
Mountains south of Lookout Pass and over the Camas Prairie where 3
to 5 inches of snow is expected. We will be issuing a Winter
Weather Advisory for snow and slick travel condtions of this
portion of the our area. The highlight will run from late tonight
through Saturday morning.

Fog will also be an ongoing concern and models show boundary layer
moisture expanding eastward across the basin overnight. I expect
fog will increase from Wenatchee to Moses Lake to Ritzville and
up on to the West Plains with time overnight. Pockets of dense fog
will be possible by early Saturday morning. /SVH

Sunday and Sunday night...High pressure will build into the region
Sunday night and this will put the region into a moist northwest
flow. Model guidance shows a fairly robust short wave disturbance
moving through the flow. The short wave combined with up-sloping
flow will result in a good chance for measurable precipitation for
the central Idaho Panhandle, south to the the Camas Prairie and
likely the Idaho Palouse. 1-2 inches of new snow will be possible,
with 3-4 inches possible for the higher mountains of southern
Shoshone county. The cool northwest flow behind the front will
keep temperatures in the lower 30s.

Monday through Wednesday...The ridge of high pressure will build
in from the west Sunday night and linger over the region through
Tuesday night. Some light snow showers may linger for the
Panhandle mountains on Monday but confidence is low. If a stray
shower or two develops it would result in light accumulations of
snow. High pressure and for the most part light winds will result
in fog/stratus formation which may have a difficult time to mix
out in the afternoons. This will keep the temperatures on the cool
side. By Wednesday afternoon guidance is showing a split flow
over the west. The steering flow shifts to southwesterly. This
will increase moisture and isentropic lift late in the day
Wednesday and Wednesday night increasing the chances for light
snow for the east slopes of the Cascade.

Thursday through Saturday...Guidance is showing a much deeper
low Thursday and Friday, but also that this will split as well.
The chance for precipitation will be on the increase through this
period. Snow levels will remain quite low so precipitation will be
mainly as light snow even in the Basin on Thursday. A warm front
on Friday will push the snow levels up for valley rain and
mountain snow Friday and Saturday. Tobin

&&

.AVIATION...
18Z TAFS: A progressive pattern is over the region right now.
Currently a weak wave is moving into the Panhandle mountains and
is kicking off some isolated rain and snow showers. Another wave
is expected later this afternoon or more likely early this
evening. With the low level being saturated it will not take much
to kick off precipitation. Model guidance is showing a lingering
band of showers across the Palouse that will effect mainly
KPUW/KLWS tonight and into Saturday morning and to a lesser
extent the KCOE/KSFF/KGEG corridor. Some of these showers could be
intense, dropping conditions quickly to IFR/LIFR. The challenge
is trying to time these which is difficult at best. Otherwise
conditons will be VFR/MVFR through the afternoon. Fog and stratus
will redevelop through the night with conditons decreasing once
again to IFR and locally LIFR. The exception being KEAT which is
stuck in fog/stratus. KEAT should show improvement around 22z-00z
but will is expected to drop back to IFR/LIFR after 10z. Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        30  34  25  32  22  32 /  20  20  10   0   0  10
Coeur d`Alene  31  34  26  31  22  32 /  30  30  20  10  10  10
Pullman        29  34  27  33  24  34 /  20  50  20  10  10  10
Lewiston       33  38  30  37  26  37 /  20  30  10  10  10  10
Colville       28  36  21  32  17  31 /  10  10  10   0   0  10
Sandpoint      29  34  26  30  23  30 /  20  20  30  10  10  10
Kellogg        29  33  26  30  23  31 /  40  50  40  40  10  10
Moses Lake     25  34  23  33  20  32 /  10  10  10   0   0   0
Wenatchee      29  34  24  34  21  31 /  10  10  10   0  10   0
Omak           29  34  21  32  18  29 /  10  10  10   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory from 1 AM to 11 AM PST Saturday for
     Lewis and Southern Nez Perce Counties.

WA...None.

&&

$$



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