Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 241303
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
447 AM PST Fri Feb 24 2017

.SYNOPSIS...
A cool and unsettled pattern will continue over the Inland NW
right into the weekend and into early next week. The main
precipitation threat will be mainly mountain based snow showers,
but a stronger system on Sunday may bring  snow accumulations to
the valleys and Basin. Temperatures will be cooler than normal for
this time of year with overnight lows in the teens and 20s and
daytime highs only in the 30s. A gradual warm up is forecast by
the middle of next week.

&&

.DISCUSSION...
Today through Saturday... A weak upper level trough will remain
fixed over the Inland NW today, while a stronger one dives down
the Washington coast today. The one over eastern Washington is the
same one that was over the region yesterday and is generally
quite weak and devoid of moisture. The coastal feature however
contains more moisture and could trigger some precipitation over
the Inland Northwest later today as low level flow backs toward
more of a southerly direction. This results in increased
isentropic ascent as well as more saturation through the dendritic
layer. However the forcing is expected to be quite weak as the
main energy with the offshore trough is expected to drift toward
the SSW through tonight. Nonetheless, the dendritic layer will
remain very unstable through the period due to persistently cold
500 mb temps so it won`t take much lifting to produce
precipitation. The best threat of showers should occur over the
northern third of the forecast area, near the Canadian Border,
however it would not be surprising to see a stray flurry or two
pops up outside of this area. Based on the strength of the ascent
portrayed by most of the model solutions, I suspect the
precipitation forecast (especially the NAM) is likely a little too
wet.

For tonight and Saturday the offshore trough continues to drop
toward the NW California coast while an unusually strong NE upper
level jet sags into the region. The positioning of the jet results
in significant warming in the mid-atmosphere which should
stabilize the dendritic layer and decrease the threat of
precipitation through Saturday morning. The precipitation threat
will ramp up again over the Idaho Panhandle by late morning as
another weak shortwave trough sweeps in from the north and
utilizes whatever instability is left ahead of the upper level
jet. Temperatures through the period will remain cooler than
normal with highs generally in the 30s and lows in the teens to
lower 20s. fx

Saturday night through Thursday: The Inland NW will be in an
active northwest flow, with cool temperatures and several
opportunities for snow or a rain/snow mix. The most significant
snow threat starts develop Saturday night late, peaks for many
areas Sunday, before the focus shifts to the southeast CWA into
Monday and Monday night. The impetus will be a shortwave trough
dropping in from BC Saturday night; its axis sags south through
the area by later Sunday into Monday, which puts the region on the
more unstable side of the feature. The core of the system pivots
west and south of the region, but it is still strong enough to
develop the threat of snow as indicated above. While the system
does not have a deep moisture tap, accumulations are expected to
be light to locally moderate. The best threat of more moderate
snows and possible advisories will lay near the Cascade crest, the
ID Panhandle Mountain zones, the Palouse, Blues and Camas
Prairie.

Then between Tuesday and Thursday the northwesterly flow
continues and weaker shortwaves pass through the region from time
to time, which will keep the occasional threat of snow alive. The
flow will keep the highest threats near the immediate Cascade
crest and over southeastern WA through the central Panhandle.
Additional chances expand across much of the region Wednesday and
Thursday. The main areas that may miss out will be the lee of the
Cascades and deeper Columbia Basin. Temperatures remain well below
normal through early next week, then moderate some toward mid-
week. So a better chance of some rain or a rain/snow mix will
develop toward mid to later next week. /J. Cote`

&&

.AVIATION...
12Z TAFs: For the first time in a long while, the forecast is
somewhat straight forward. Fog and stratus has been slow to form
this morning and the latest satellite imagery suggests most of it is
poised near the WA/ID border. It has been slow to expand westward,
but it will occasionally impact COE and PUW with MVFR cigs and a
small chance of IFR visibility values at COE. While we can`t
entirely rule out the chance of these low clouds spreading into GEG,
LWS and SFF, the satellite trends don`t support that notion. MWH and
EAT will very likely remain at VFR conditions. Later today a weak
disturbance will drop into the region from the NW which will bring a
small chance of light snow showers. If they hit any of the airports
we suspect conditions will remain in the vfr range. Overnight the
threat of snow showers will decrease and high clouds will thicken
from the west. This should greatly decrease the threat of fog
reforming late in the forecast period. fx

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        34  19  33  24  34  22 /  10  10  10  30  60  40
Coeur d`Alene  34  16  33  23  34  21 /  10  10  10  50  60  50
Pullman        35  21  35  25  36  24 /  10  10  10  30  70  60
Lewiston       39  25  40  28  41  28 /  10  10  10  20  60  40
Colville       35  16  34  24  35  20 /  20  10  10  30  50  20
Sandpoint      33  17  33  23  33  20 /  20  10  20  60  60  40
Kellogg        32  19  32  24  33  23 /  20  10  40  60  70  60
Moses Lake     38  17  36  25  36  23 /  10   0   0  20  30  20
Wenatchee      39  17  34  24  35  22 /  10  10   0  30  40  20
Omak           38  17  33  24  34  22 /  10  10   0  40  50  20

&&

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

$$



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