Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 202135
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
235 PM PDT Wed Sep 20 2017

.SYNOPSIS...
Rain showers will decrease through the evening hours across
eastern WA and north ID. Hit and miss showers are expected
Thursday for most of the region before a drier and warmer weather
pattern starts Friday and kicks in for the weekend and early next
week.

&&

.DISCUSSION...
Tonight through Friday Night: Weather disturbance is moving across
southern Washington this afternoon. 500 mb low is currently just
west of Ritzville. Cold 500 mb temps of -25C will keep instability
showers going across the region this afternoon. Thunderstorms have
remained south of our forecast area down around the Tri-Cities and
north of Walla Walla, but cannot rule out a slight chance of
thunderstorms through early this evening across the SE corner of
WA and portions of the LC Valley and Camas Prairie. As this wave
exits, the backside of the trough, in the form of northerly winds
and an increase of clouds from the north will move in overnight.
Some of the hi-res models are showing as the backside swings
through overnight and tomorrow the threat of showers will increase
from the Okanogan Valley after midnight and then move southeast.
Showers could be to the Spokane and Columbia Basin area by the
morning commute, and then to SE WA and the ID Panhandle in the
aftn. We remain in this northerly flow Thursday night into Friday.
Friday there will be less showers across the region, mainly
confined to the Cascade crest and the mountains of north ID.
Temperatures will be quite cool for this time of the year, about 5
to 15 degrees below average. Valley lows will be in the mid 30s to
low 40s with some isolated pockets of below freezing temps. Valley
high temps will be in the 50s to mid 60s. /Nisbet

Saturday and Sunday: For the weekend conditions will be improving.
By Saturday the trough axis has been pushed into Idaho and
Montana which will keep most of the mid level moisture to our east
and the showers as well. Under this drier northerly flow the only
rain chances will be over the extreme eastern mountain zones, and
any amounts would be very light. On Sunday another surge of mid
level moisture comes down from BC over the incoming ridge, which
will increase our cloud cover, but likely won`t result in any rain
showers. The GFS has introduced some showers over the Cascade
crest Sunday, but this has only showed up in the last run and none
of the other synoptic models agree, so have kept showers out of
the forecast. Temperatures will still feel fall-like, rising to
the mid to upper 60s by Sunday.

Monday through Wednesday: Continued warming and drying is favored
under this pattern, as the high pressure ridge moves in. Models
disagree on potential rain, however. The EC and Canadian want to
give us more of a dirty ridge with showers overtopping the ridge
on or about Mon night/Tuesday, mainly in our mountains. Not enough
consensus this far out to add any showers to the forecast at the
time, but it bears watching. Temperatures will inch up a few
degrees each day reaching low to mid 70s by mid week. This would
put us at or even slightly above seasonal normals for late
September. /bw

&&

.AVIATION...
18Z TAFS:A disturbance is tracking along the WA/OR border today.
This will focus the best chance of rain and rain showers across
southern WA. Showers could extend as far north as KGEG-KSFF-KCOE
taf sites aft 21Z. Showers are expected to decrease after 03z,
and could see cigs drop to MVFR to local IFR for a few hours.
Partial clearing possible early this evening, before mid and high
clouds increase from the north overnight and spotty mountain
showers. Showers are expected to develop around 14Z around
Spokane/COE area.



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        39  53  40  57  41  62 /  50  40  10  10  10  10
Coeur d`Alene  37  52  35  56  37  61 /  70  50  10  10  10  10
Pullman        37  53  37  57  39  59 /  60  30  10  10  10  10
Lewiston       42  59  41  62  43  66 /  50  30  20  10  10  10
Colville       38  57  36  61  38  67 /  40  40  10  10  10  10
Sandpoint      37  51  34  56  34  59 /  40  60  20  10  20  10
Kellogg        36  48  33  52  34  56 /  70  60  30  20  20  10
Moses Lake     38  62  42  64  41  69 /  10  30  10   0  10  10
Wenatchee      44  61  44  65  45  69 /  10  20  10   0  10  10
Omak           42  61  40  64  41  69 /  30  20  10   0  10  10

&&

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

&&

$$



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