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Area forecast discussion 
National Weather Service Spokane Washington
218 PM PDT Tuesday Sep 2 2014

Synopsis...
breezy winds are expected this evening with the passage of a cold
front. The front will also bring the potential for showers and
thunderstorms to the Idaho Panhandle and northern Washington
tonight into Wednesday. Thursday morning will be cold with low
temperatures down into the lower to mid 30s for the Mountain
Valley locations. The return of high pressure Thursday through the
weekend will bring several days of dry weather, light winds, and
warmer temperatures.

&&

Discussion...
tonight: showers, perhaps some thunder, and breezy conditions are
expected. A cold front and dynamic upper trough were pushing into
western Washington this afternoon. The cold front tracks east of
the Cascades early this evening, into the Panhandle around
midnight and exits into Montana by Wednesday am. The upper trough,
however, will be slower to exit. Early this evening models keep
the main precipitation over the Cascades with the cold front and
along the Canadian border closer to the warm front. As the cold
front and upper trough start east of the Cascades, a surface
trough/trowal starts to become established across the northern
mountains. Precipitation is expected to increase in coverage
around the Okanogan, the mountains of northeast Washington and, by
late evening or early overnight, over the northern Panhandle.
Showers are also expected to develop over portions of the basin
through central/southern Panhandle, especially from 8 PM and
beyond. However, being more removed from the upper support, these
should be more isolated to scattered in nature. This means not
every location will get wet, especially the further south and west
into the basin and south toward the l-c valley. As the night
progresses into Wednesday morning the upper trough pivots east
toward the Washington/Idaho border, with the trowal and moisture wrapping
just behind it. This will only serve to keep precipitation chances
high across north-central and northeast Washington and chances going
across the upper Columbia Basin through Palouse and central
Panhandle. Smaller chances will be found toward the l-c valley and
Camas Prairie.

As for the thunder prospects, modest cape is depicted this
evening around the Cascade crest and toward the northern
mountains. This abates through the evening and overnight, but weak
to moderate elevated instability lingers across northeast Washington and
East-Central Washington and north Idaho overnight. So look for some thunder
chances across the Cascades through northern Panhandle, with the
main threat shifting toward northeast Washington and north Idaho overnight.
Thunder coverage is not expected to be large, but storms may be
capable of heavy downpours and gusty winds.

As for the winds, WV imagery shows good darkening with the upper
trough/vorticity Max and this suggests some good mixing with the
incoming front. So look for winds to really pick up as we go into
late afternoon and remain breezy to locally windy through this
evening. The strongest winds are expected closer to the Cascades,
especially near the ridge-tops. Lower elevations near the Cascades
could see sustained winds of 15 to 25 mph, with gusts around 30 to
40 mph. This includes the Wenatchee and Waterville Plateau area.
Nearby mountain-top winds, however, could gust between 50 to 60
mph. We will have to watch any convection that might fire in this
region for potentially strong winds reaching the lower elevations.
Speeds will abate overnight, but in a gradual way. The main area
that should miss out any strong winds will be toward the sheltered
valleys of northeast Washington and north ID, with speeds in the 5 to 15 mph
range. /J. Cote'

Wednesday through friday: the incoming upper trough will be
sitting over the forecast area as dawn breaks on Wednesday. Models
are in good agreement regarding the strength...track and speed of
this system. The trough cusp will feature areas of moderate to
strong vorticity dynamics with cooler air aloft decreasing
stability. Present for fuel will be around 3/4 inch precipitable
water which is very adequate for showers. All-in-all it appears
this system will bring a moderate amount of rain to parts of the
region...likely north and east of a line from Omak to
Pullman...during the day tomorrow. Character of precipitation will
probably be hit-and-miss showery over the northeast basin with
frequent or intermittent showers. The peripheral zones from the
east slopes of the Cascades to the upper Columbia Basin and the
Palouse will experience more isolated and spotty showers. The deep
basin and Cascades Lee zones will probably only receive breezy
winds and clouds from this wave passage.

The upper trough will move out quickly on Wednesday night with a
general drying and clearing trend from west to east as the
backside ridge featuring dry northwest flow kicks in by Thursday
morning. A second weak wave will brush along the Canadian border
Thursday night but little beyond some enhanced cloud cover over
the northeast is expected at this time.

Temperatures particularly Thursday morning will have a nip of
autumn to them...with overnight lows into the upper 30s possible
in the sheltered valleys north and east of the basin...along with
some patchy valley fog. Daytime highs on Wednesday will be well
below normal but begin a recovery Thursday as things dry out and
the ridge builds back. /Fugazzi

Friday night through tuesday: a dome of high pressure will expand
over the inland northwest over the weekend bringing abundant sunshine...above
normal temperatures...and light winds. 850mb temperatures will
warm between 19-20c yielding temperatures in the 80's to low 90's.
The ridge of high pressure will weaken and shift west at the start
of the work week setting up persistent northwesterly flow into
ern Washington. The transition to northwest flow will be marked by a shortwave
trof passage during the Sunday night/Monday time-frame. This
system will bring gusty winds...chance for showers...and return
to cooler...September like temperatures. Overall...deterministic
and ensemble member solutions are in good agreement and any
foreseeable changes will likely deal with timing and depth of the
Sunday night/Mon feature. GFS progs look like a Carbon copy of the
next 24 hours while the European model (ecmwf) is a tad weaker. Both solutions
support the best chance for showers mainly along the Cascade crest
and northern mountains of Washington/Idaho and likelihood for breezy
conditions. 850mb temperatures cool to 15c Monday then 13c Tuesday
knocking temperatures back into the 70's to lower 80's. /Sb

&&

Aviation...
18z tafs: a strong cold front will cross east of the Cascade mtns
late this afternoon through this evening. This front will produce
gusty winds from the west and will arrive at keat and kmwh between
23-02z and then push into the kgeg, ksff, kcoe, kpuw and klws taf
sites around 03-04z. Winds will remain breezy through the
overnight hours. Showers and thunderstorms are expected across the
northern mtns late this afternoon into tonight and then begin to
push into kgeg, ksff and kcoe and possibly as far south as kpuw
Wednesday morning and last at least through the end of the taf
period. Conditions will remain VFR at all taf sites with the
possible exception of kcoe after 12z Wednesday if shower
development is more intense and widespread than currently
forecast. /Mjf



&&

Preliminary point temps/pops...
Spokane 50 64 47 74 49 79 / 60 50 20 0 0 0
Coeur D'Alene 50 60 43 74 44 79 / 70 60 40 0 0 0
Pullman 46 65 41 74 43 81 / 20 30 10 0 0 0
Lewiston 54 72 50 79 51 85 / 20 10 10 0 0 0
Colville 48 65 40 77 41 82 / 60 60 30 0 10 10
Sandpoint 46 58 40 72 40 76 / 70 80 60 10 10 10
Kellogg 47 55 40 70 43 75 / 50 60 50 10 0 10
Moses Lake 52 76 49 79 49 85 / 20 10 0 0 0 0
Wenatchee 56 76 55 78 54 84 / 20 10 0 0 0 0
Omak 54 73 47 79 48 84 / 50 10 10 0 0 0

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...&&

$$

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