Area Forecast Discussion
Issued by NWS Spokane, WA

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741
FXUS66 KOTX 232357
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
357 PM PST Thu Nov 23 2017

.SYNOPSIS...
Wet and unsettled weather will linger through the week as a
series of storm systems brings several rounds of precipitation to
the region. Cooler and unsettled conditions this weekend will
result in lowering snow levels as travelers are heading home.
Windy conditions are once again possible on Sunday.

&&

.DISCUSSION...
Tonight through Friday night...A robust cold front will finish
transiting the forecast area this evening and pass off to the
east. Windy conditions early this evening will gradually subside
but likely remain on the breezy side over the exposed terrain of
the basin through the night. This will serve to limit any fog
formation to the more sheltered northern valleys. Precipitation
will be decreasing as well from west to east this evening...and by
dawn the only further threat should be near the Cascade crest
from slop over as a weak and more temperate origin moderate
Pacific fetch impinges on the Cascades.

Friday and Friday night...even into Saturday will be a quiet but
rather cloudy break period over the region. A new upper level
trough will be digging offshore promoting a weak rideg over the
forecast area. This ridge will be rather dirty however...as the
aforementioned moisture feed continues to flow through the mid and
upper level air mass gradually becoming directed from westerly
into the forecast area...to a more southwesterly trajectory into
Canada by Friday night. This moisture feed does have the potential
to produce some light mountain snow while it is washing over the
area on Friday...limited to the mountains...but travelers
returning home across the Cascades should be aware of some minor
to locally moderate snow accumulations near the pass levels on
Friday. The Idaho passes may pick up some minor accumulations and
little if any impacts are expected for travelers going east to
Montana.

Saturday through Monday...The next significant storm system in
the continuing active pattern will overspread the region Saturday
afternoon in the west and spread across the area Saturday night
and Sunday. A new and deep upper level trough will promote a deep
surface low pressure migrating north just off the coast. The
associated warm front will take shape over eastern Washington move
south to north through the forecast area...fed by another
subtropical origin moisture feed. The Cascades with moist
isentropic ascent coupled with favorable upslope low level flow
will bear the brunt of this storm. Snow levels will be
rising...and it is expected that valleys in the Cascades will see
mostly rain while above 3500 to 4000 feet generally moderate to
locally heavy accumulations of snow are expected. The
southeasterly low level flow into this distant low pressure will
tend to minimize precipitation over the Idaho Panhandle during the
warm front phase.

The trailing cold occluded front will sweep through the region on
Sunday...bringing another focus of valley rain and mountain snow
this time to the rising terrain of the eastern zones as flow aloft
shifts west promoting downslope in the basin and upslope into the
Idaho Panhandle and northeast Washington mountains. However...snow
levels will be back up around 8000 feet during this round of
precipitation and won`t begin to fall until after the FROPA and as
precipitation tapers off so no significant snow issues are
expected in the Idaho passes. Breezy to windy conditions are
expected on Sunday afternoon and evening with a similar set up to
the current windy pattern but gradient and gust potential does not
look as strong as today.

On Monday the latest model runs have agreed on a plausible
solution depicting the parent offshore trough ejecting inland and
splitting with the main dynamic foot of the trough sweeping
through Oregon and the Great Basin. It looks like eastern WA will
be under a fairly quiet zonal orographic northern branch flow
featuring mainly scattered valley rain and mountain snow showers
concentrated over the Panhandle mountains and probably absent from
the deep basin in the Cascades rain shadow.

Tuesday through Thursday...Model agreement breaks down through the
end of the extended period. The forecasts for Tuesday through
Thursday is a low confidence conjecture. What models have in
common is a continued active and progressive flow regime with
probably some more moisture feeds penetrating the region on one of
these days...at this time most likely Wednesday but each model
run seems to change. So...at this time Tuesday will be forecast as
a benign break period...Wednesday the next risk of valley
rain/mountain snow...and Thursday another break.

Throughout the entire forecast period despite occasional cold
front passages...the mean southwesterly flow regime argues
strongly for continued above normal temperatures. /Fugazzi

&&

.AVIATION...
00Z TAFS: A cold front laying from KSZT to KYKM at 00Z will move
southeast off into MT and central ID by 03Z. Eastern TAF sites
will be subject to occasional -SHRA with brief MVFR conditions
until 02z-03Z with gusty southwest winds. Mainly VFR conditions
with decreasing winds expected during the night. Early Friday
morning some upslope IFR or low MVFR stratus ceilings are
possible at the KGEG area TAF sites and KEAT which is in a
protected area against the Cascades. Any stratus will burn off by
18Z with VFR conditions expected through 00Z Saturday. /MJF

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        36  45  32  45  38  50 /  20  10  10  10  50  60
Coeur d`Alene  36  44  32  45  36  49 /  50  10  10  10  50  60
Pullman        38  46  32  47  41  52 /  80  10   0  10  30  60
Lewiston       40  52  33  51  41  55 /  90  10   0  10  20  60
Colville       34  44  33  42  35  47 /  30  10  20  10  60  60
Sandpoint      35  41  32  42  33  47 /  50  30  20  10  60  70
Kellogg        35  41  31  44  35  47 /  70  30  10  10  40  80
Moses Lake     35  50  31  45  35  50 /   0  10  10  30  40  40
Wenatchee      36  47  31  41  36  46 /  10  10  10  50  70  40
Omak           35  46  32  42  36  47 /  10  10  10  20  80  50

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory until 6 PM PST this evening for Central Panhandle
     Mountains-Lewis and Southern Nez Perce Counties-Lewiston
     Area-Northern Panhandle.

     Wind Advisory until 6 PM PST this evening for Coeur d`Alene Area-
     Idaho Palouse.

WA...Wind Advisory until 6 PM PST this evening for Lower Garfield and
     Asotin Counties-Spokane Area-Upper Columbia Basin-
     Washington Palouse.


&&

$$



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