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Area forecast discussion 
National Weather Service Spokane Washington
235 PM PDT Tuesday Sep 30 2014

Synopsis...
scattered showers and breezy conditions will come to an end
tonight. High pressure will gradually build in through the weekend
and linger into the middle of next week. This will result in
generally dry weather with temperatures warming to above normal by
the weekend.



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Discussion...
tonight and wednesday: an upper level trough will pivot through
eastern Washington into north Idaho this evening. As it does, it
will bring a chance of showers to the northern mountains, northern
Columbia Basin and most of north Idaho. A few embedded
thunderstorms are possible through late this afternoon. This
convection will be diurnally driven and the clouds with showers
will decrease rapidly with the loss of daytime heating early this
evening. Westerly winds will remain gusty from the Lee of the
Cascades and across the lower Columbia Basin with speeds of 20 to
25 mph. By tonight, the flow aloft becomes northerly and drier. A
ridge of high pressure building off the Washington coast, will
push inland on Wednesday and give drier and sunnier conditions.
Temperatures will cool slightly overnight into the upper 30s to
lower 40s. And in sheltered areas, expect even cooler conditions
under the clearing skies. Anticipate some patchy fog in many of
the northern valleys, especially in the locations that the showers
tracked through today. The fog will be short lived and expect
mostly sunny skies for the rest of the day under lighter winds.
Daytime temperatures will continue to be cool, remaining at or
slightly below normal./ Rfox

Wednesday night through saturday: a Flat Ridge of high pressure is
expected to bring a prolonged period of dry weather and mild
temperatures to the inland northwest from mid-week through the
weekend. The 12z model runs are in decent agreement that the polar
jet will remain far enough north through the second half of the
week that precipitation chances will be largely north of the
Canadian border. Slight chances for rain are in the forecast for
the northern Cascades and the high terrain along the Canadian
border for Friday and Saturday, but nearby valley locations should
remain dry. Look for a gradual warming trend Thursday through
Saturday with temperatures climbing a bit above average by the
weekend. /Gkoch

Saturday night through Tuesday...an upper ridge over the western
U.S. Is expected to remain strong enough in the extended forecast
period to deflect a moist zonal flow north of the area across
central British Columbia. The GFS, ECMWF, and Canadian models are
in good agreement with this idea. The inland northwest will be
the warm and stable side of the jet stream. Models show some
increase in lower level moisture during the period as some of the
very moist flow over British Columbia clips the area. This will
raise dew points into the 40s to lower 50s which will aid in mild
night time lows. Periods of mid/high clouds may also assist with
warmer nights. In addition...850mb temps in the 14-17c range will
result in valley highs mainly in the 70s with a few lower 80s in
the warmest spots such as Wenatchee, Moses Lake, and Lewiston. The
increased low level moisture content and upslope westerly flow may
be enough to ring out a few light showers near the Cascade crest
and in the mountains of north Idaho...with the better chances
north of the Canadian border. Jw

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Aviation...
18z tafs: a cold front moved through eastern Washington and north
Idaho overnight. This afternoon, the Idaho Panhandle will be
squarely under the 500mb cold pool. Look for diurnally driven
showers to increase around 20z and persist until 02z. Some of the
strongest cells may produce a couple of lightning strikes and
brief heavy downpours. Thunderstorms will be handled on a
"nowcast" basis as we monitor radar trends this afternoon. The
Spokane, Coeur D'Alene, and Pullman tafs may require an amendment
to add a short-lived thunderstorm. As the sun sets, skies should
clear quickly with the loss of afternoon heating. /Gkoch

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Preliminary point temps/pops...
Spokane 41 62 40 64 42 70 / 20 0 0 0 0 0
Coeur D'Alene 41 62 41 64 40 70 / 30 0 0 0 0 0
Pullman 39 63 38 65 39 72 / 20 0 0 0 0 0
Lewiston 46 69 46 70 45 77 / 20 0 0 0 0 0
Colville 38 67 39 68 38 72 / 20 0 0 0 10 10
Sandpoint 39 60 37 62 35 66 / 50 0 0 0 0 10
Kellogg 39 55 40 60 40 65 / 60 10 0 0 0 0
Moses Lake 41 70 40 69 40 75 / 0 0 0 0 0 0
Wenatchee 47 69 46 69 48 74 / 0 0 0 0 0 0
Omak 40 67 39 67 44 74 / 10 0 0 0 10 10

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

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