Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 201330

Area Forecast Discussion
National Weather Service Spokane WA
530 AM PST Fri Jan 20 2017

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 colder weather pattern is expected next week.



Today through Saturday: The Western United States will continue
to feature the most active weather over the continent. Through the
weekend the Polar Jet will be focused over California as low
pressure churns off the coast of Washington. A series of weak
upper level disturbances will pivot across the Inland Northwest
today through the weekend. With low pressure off the coast, our
region will experience a prevailing easterly wind providing low
level upslope flow into the Cascades. The combination of upslope
flow into the East Slopes and moist warm advection aloft will
produce periods of light snow for places like Leavenworth,
Wenatchee, Lake Chelan, and the Methow Valley. With the core of
jet well south of our region, we don`t expect any strong upper
level forcing and most of the model omega is progged to be below
700mb which is really low in the atmosphere. Weak synoptic forcing
and low level omega suggests that precip intensity will be fairly
light. Look for 1 to 2 inches of accumulation during the day, and
another couple inches tonight. The Moses Lake area has the
potential to have a mixed bag of light precipitation this
afternoon and this evening. Surface temperatures near freezing and
the potential for a warm layer aloft suggests the potential for
rain in the afternoon and early evening (possibly mixed with
sleet) before changing to light snow overnight.

On Saturday, there is reasonable model agreement that there will
be a break in the light snow in central Washington as a shortwave
trough shears into northeast Washington and north Idaho. Snow
accumulations for places like Spokane, Colville, Sandpoint, and
Bonners Ferry look to be minor, a half inch or less. If the timing
of the NAM and GFS verifies, snow chances for accumulating snow
will increase Saturday night along the East Slopes of the
Cascades. Once again low level easterly upslope combined with our
next shortwave will bring the chance for an inch or two of snow to
places like Leavenworth, Lake Chelan and the Methow Valley. /GKoch

Sunday through Tuesday night...An occluded front will swing
through the region Sunday into Sunday evening resulting in
widespread precipitation for most of the region. A deep low
(around 960mb) off the WA/OR coast near 130W will result in
southeasterly low level flow providing added upslope and
isentropic lift into the East Slopes of the Cascades, Wenatchee
area, Waterville Plateau, Okanogan Valley and Highlands where
moderate snow accumulations are possible. Surface temperatures in
the lowest elevations along the Columbia, Okanogan, and Wenatchee
rivers may rise to 33-35 Sunday which could limit snow
accumulations below 1000 feet but confidence in this detail is low
at the moment. Elsewhere only light snow amounts are expected and
mainly above 1500-2000 feet. Strong downslope flow into the
Lewiston area results in lower confidence for precipitation and
have limited POP`s in this area to chance. After this a cooler and
drier northerly flow develops for Monday and Tuesday as an upper
ridge builds just off the coast. While no deep freeze is expected,
temperatures are expected to drop to slightly below normal values
with lows mostly in the teens to mid 20s and highs in the upper
20s to mid 30s.  JW

Wednesday and Thursday: This period remains characterized by drier
and slightly cooler weather than the previous weekend, with the
upper ridge and northerly winds bringing drier and colder air
south. This high pressure with moist lower levels mean freezing
fog will be likely in the low lying areas and low stratus will
stick around the region through Thursday with little wind
expected. Highs look to be around 10 degrees colder than normal,
in the mid to upper 20s. /bwilliams


12Z TAFS: Light north winds have brought improving visibility to
Moses Lake and Ephrata. The pressure difference between a low off
the coast and high pressure east of the Continental Divide should
keep the northeasterly gradient strong enough to keep the fog out
of these central WA airports. Shallow ground fog around Spokane
should be short-lived this morning as east or northeast winds
should increase around sunrise. Accumulating snow is expected at
Wenatchee and Chelan by mid to late afternoon. Air temps will be
at or above freezing during the afternoon which may allow snow to
melt on the runway, but ground temps are quite cold. As the sun
sets, look for a refreeze and the potential for a couple inches of
accumulation through the evening. /GKoch


Spokane        38  28  34  25  35  24 /  10  20  40  20  60  40
Coeur d`Alene  39  28  35  26  35  24 /  10  10  30  30  50  50
Pullman        40  30  35  27  36  26 /  10  20  30  20  60  40
Lewiston       43  32  38  29  38  28 /  10  10  30  20  30  30
Colville       36  26  33  27  36  25 /  20  10  40  40  40  60
Sandpoint      38  28  33  27  35  27 /  20  10  40  40  40  70
Kellogg        36  26  33  25  33  25 /  10  10  40  30  50  60
Moses Lake     35  29  34  26  35  22 /  50  60  20  20  80  30
Wenatchee      34  30  33  27  32  23 /  80  90  30  50  80  40
Omak           37  30  34  27  34  23 /  30  60  60  50  80  60



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