Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 202338
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
338 PM PST Fri Jan 20 2017

.SYNOPSIS...
Periods of light snow are expected today and into the weekend for
the East Slopes of the Cascades. For the remainder of the Inland
Northwest the best opportunity of accumulating snow will be on
Sunday. A drier and cooler weather pattern is expected next week
with the possibility of deteriorating air quality as the week
wears on.

&&

.DISCUSSION...

Tonight and Saturday...Weak frontal zones pivoting around the outer
edges of an area of low pressure just off the Pacific Northwest
Coast will overrun lower level cold air as the move over Eastern
Washington and North Idaho tonight and Saturday. The result will be
some potential for precipitation, primarily snow but a rain/snow mix
possible further south over the basin, tonight and into tomorrow.
The greatest chance of snow remains where these low level east winds
are upslope which is over the East Slopes North Cascades and close
vicinity. /Pelatti

Saturday night through Sunday night: A weak upper level
disturbance will push across the region Saturday night followed by
a frontal occlusion on Sunday. Dynamics associated with the upper
level wave Saturday night will be very weak with generally light
precip amounts regionwide. Upslope flow into the east slopes of
the northern Cascades will produce the best lift due to
orographics. Precip type will be in the form of snow with around 1
to 3 inches expected. Precip type will be snow as well across the
northern mountains of northeast WA and into the ID Panhandle, but
amounts will be light. Highs on Saturday will be in the mid 30s
in the Moses Lake Area and Upper Columbia Basin with temperatures
then expected to drop into the mid to upper 20s Saturday night. I
don`t think we will see enough moisture to erode this warm layer
complete and I added a chance of freezing rain for these areas.
Amounts will be light in the neighborhood of up to a few
hundredths, but it could be enough to result in a light glaze of
ice overnight into Sunday morning. It is possible that this small
chance for freezing rain extends into the WA Palouse and Spokane
Area, but confidence is even less for these areas.

The best chances for precip will come Sunday afternoon and
evening. An occluded front will sweep across with the parent low
well offshore at 46N 133W. Upper level dynamics will be more
favorable with this wave. Easterly flow will continue to result in
favorable orographic lift across the east slopes of the northern
Cascades. An additional factor will be moderately steep mid level
lapse rates of 6.5 C/km. Although I don`t agree with the NAM`s
depiction of precip amounts, I have to consider the possibility of
convective enhancement. I expect the east slopes of the northern
Cascades to pick up 3 to 5 inches with locally higher amounts up
to 7 inches possible. Most other areas surrounding the Columbia
Basin will see 1 to 3 inches of snow or so. The front will exit
Sunday night with fog possible in the Moses Lake Area and the
Upper Columbia Basin overnight into Monday morning as mid and high
levels clear out. /SVH

Monday through Friday...Models are in decent agreement with the
overall field of motion through the extended period. Initially on
Monday an upper level trough will reside over the region but with
any dynamic support focused well south of the region in the Great
Basin. Still...there may be a wrap-around moisture axis close to
the south of the region...and an ill defined short wave dropping
out of Canada so while conditions will be increasingly dry there
is still a small chance of light snow...not expected to accumulate
appreciably even if it occurs...over the eastern third of the
forecast area Monday through Tuesday.

After this parting shot confidence is growing that the region will
come under the influence of a ridge aloft featuring dry northerly
flow aloft and a broad relatively placed high pressure at the
surface through the rest of the work week. This pattern will
promote a typical deep winter inversion pattern with morning lows
generally in the teens and and daytime highs in the 20s...a bit
below average but not arctic-like. Winds will be light and air
quality issues may become germane as the week wears on. A
coordination call with Air Quality authorities will occur on
Monday and further action will be decided upon as far as any
necessary highlights. The only weather issues will be the
likelihood for increasing low clouds and freezing fog each day
with no precipitation expected other than that which is squeezed
out of the stratus in the form of flurries or patchy freezing
drizzle. /Fugazzi

&&

.AVIATION...
00Z TAFS: An upper level trough off the Pacific coast will send a
shearing deformation moisture band through the region from
southwest to northeast tonight and Saturday morning bringing a 4
to 6 hour period of light snow to most TAF sites. Ceilings and Vis
during this weak storm system will be generally MVFR over the
eastern TAF sites late tonight and early Saturday and and low
MVFR or IFR over the KMWH and KEAT TAF sites mainly tonight. In
the wake of this system IFR conditions under low stratus may
persist at KEAT and KMWH through much of Saturday. /MJF


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        26  34  26  34  24  32 /  20  50  20  70  90  20
Coeur d`Alene  25  35  25  34  24  34 /  10  50  20  60  90  20
Pullman        28  35  28  35  25  31 /  20  40  20  70  60  20
Lewiston       31  38  30  38  28  35 /  10  40  20  60  30  20
Colville       26  33  28  34  25  32 /  10  60  50  40  90  20
Sandpoint      27  33  27  34  27  33 /  10  60  40  40  90  20
Kellogg        26  33  25  33  25  31 /  10  50  30  50  90  20
Moses Lake     25  34  25  34  22  32 /  60  30  20  90  20  10
Wenatchee      28  33  26  32  25  29 /  90  40  50  90  20  10
Omak           26  34  26  33  25  31 /  60  70  70  90  80  20

&&

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

$$


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