Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 022343
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
343 PM PST MON MAR 2 2015

.SYNOPSIS...
A weather system will pass through this evening, with potential
for scattered snow showers along with breezy conditions across
much of the region. The snow shower threat and winds abate
overnight into Tuesday.  Much colder air moves in behind this
system, with temperatures well below average for the middle of the
week. A dry period, with moderating temperature will follow for
the end of the week.

&&

.DISCUSSION...

Tonight and Tuesday: The snow shower threat will dissipate
across the Inland NW tonight on a breezy north wind, leading to a
drier and colder Tuesday. This evening a mid-level shortwave is
tracking across the eastern third of WA and north ID; it is
projected to sag toward central and southern ID late this evening
into the overnight. As that shortwave tracks by us it is
accompanied by a pool of colder 500mb temperatures, in the -30 to
-35 C range. This leads to some unstable lapse rates and so the
accompanying potential for convective showers. Furthermore, a
deformation axis/surface trough lingers across the eastern third
of WA through the night, though it does lose some of its
resolution overnight.

All of this means a threat of scattered to locally numerous snow
showers through, especially early this evening, between 00-04Z (4
to 8 PM), before the drier northerly flow take hold and the
precipitation threat begins to wind down. The deformation
axis/trough itself should help to focus those showers and right
now that been somewhat consistently across northeast mountain and
Spokane/C`dA area.

The convective nature of the system makes pinning down the
precise snow accumulations difficult in the valleys. Values could
range from nothing or a trace to as much as 1 inch or so under the
heaviest bands. The road and air temperatures, however, should
keep the snow from sticking to the roads and other surfaces
initially. However later this evening and overnight any
precipitation that falls would have every opportunity to freeze on
surface. How much of an impact that would have later this evening
and for the Tuesday morning commute is less certain, because areas
that would see little to no accumulation may have no problems but
if you happen to be that spot that gets more precipitation you be
more prone to slick spots. As for the mountains, snow amounts
could be in the 1 to 3 inch range, when all is said and done for
the entire system, with isolated higher amounts.

Late this evening and overnight, the main shower threat is
expected to shift toward the Central Panhandle and Camas Prairie,
and possibly the Blues. A secondary threat will linger within the
northeastern mountains, with a weak secondary wave dropping by and
the weakening deformation axis in the region. Tuesday looks mainly
dry and partly cloudy to clear.

Winds will be an issue this evening with the shortwave pushing in
coupling with a tightening pressure gradients. The strongest winds
are expected through the Okanogan Valley, where some channeling is
expected. However speeds will also be up across the remainder of
eastern WA and the north ID valleys. On average we are looking for
10 to 20 mph, with gusts to 30 mph. However in the Okanogan
Valley speeds of 15 to 30 mph with gusts to 40 mph are possible.
Going into the overnight and Tuesday the gradients begin to
slacken and the atmosphere decouples, so overall speeds should
begin to abate.

Temperatures tonight are expected to drop below normal thanks to
the push of colder, drier air from the north. Values could be some
10 or so degrees below average. This carries into Tuesday
afternoon with highs expected to remain below normal by 5 to 10
degrees. /J. Cote`

Tuesday night through Monday: A ridge of high pressure will be the
dominate weather feature through the period delivering mostly dry
conditions and a gradual warming trend. The only exception is
within the Friday time-frame. Models suggest the ridge will
flatten enough allowing a weak disturbance to skirt the
International Border before dropping southeast down the MT/ID
border. The ECMWF is an outlier at this time indicating the
potential for a tenth or so of liquid while the GFS/Canadian/Ensemble
Means only bring through trace amounts of liquid. Needless to say,
confidence is low regarding this feature and precipitation chances
but this looks to be the only chance for precipitation through
Monday. Temperatures will start off cool with 850mb temperatures
on the order of -5C but warm near 3-8C by the weekend. This will
equate to warming temperatures each day with temperatures expected
to warm well above normal by the weekend.

There are signs in the extended models that a large scale pattern
change will be possible which features the reversal of the Eastern
US trough and Western Ridge. There are some timing differences but
looks to occur around mid to late next week. Climate Prediction
Center looks to favor this change as well with the 8-14 day
outlook predicting the potential for warmer and wetter conditions
on the West Coast... conducive of the incoming trof and
mild/wetter southwest flow. /sb



&&

.AVIATION...
00Z TAFS: A shortwave will drop south across the east WA/north ID
between 00-06Z, with scattered snow showers. With unstable lapses
accompanying these some of these could be locally heavy, producing
brief reductions to MVFR conditions, especially around
GEG/SFF/COE. They will be more isolated toward PUW/LWS. The threat
will wane after 03-04Z over most locations, but could some
potential may linger through 08Z. EAT/MWH will mainly dry, with
only the off chance of a flurry. Otherwise look for VFR conditions
here. Expect breezy conditions around 15 to 25kts, with gusts to
30 around MWH. Other breezy conditions are expected at EAT, as
well as GEG to COE with the incoming shortwave. However speeds
will be a bit less, at 10 to 20kts. Speeds in general will abate
after 08-11Z. /J. Cote`


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        18  37  17  43  23  48 /  50   0   0   0   0   0
Coeur d`Alene  16  37  14  43  21  49 /  50   0   0   0   0   0
Pullman        18  37  17  43  26  51 /  30   0   0   0   0   0
Lewiston       26  40  20  47  27  54 /  20  10   0   0   0   0
Colville       21  41  16  45  22  50 /  50   0   0   0   0   0
Sandpoint      17  34  12  41  21  44 /  50   0   0   0   0   0
Kellogg        17  32  13  40  22  45 /  70   0   0   0   0   0
Moses Lake     22  44  20  48  26  53 /  10   0   0   0   0   0
Wenatchee      27  45  20  50  29  54 /   0   0   0   0   0   0
Omak           22  45  19  47  24  52 /   0   0   0   0   0   0

&&

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

$$




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