Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 272329

Area Forecast Discussion
National Weather Service Spokane WA
429 PM PDT Tue Sep 27 2016

Mild and dry weather will be in place tonight and Wednesday.
Breezy winds will continue down the Okanogan Valley and into
portions of North Idaho. A pattern change is expected to arrive
late in the week with chances for showers beginning Thursday and
continuing into the weekend. By Saturday and Sunday, afternoon
temperatures will likely be in the 60s...possibly cooling further
into the 50s next Monday.


Tonight through Thursday: The cold front sagging into the region today
will stall and begin to dissolve before reaching southeastern WA.
The main weather impacts will continue to be breezy northerly
winds. Breezy north winds will persist in the Okanogan Valley
spilling into the western Columbia Basin through Wednesday
morning. We are also looking for an increase in northeast winds
down the Purcell Trench impacting locations like Sandpoint and
Coeur D Alene. Speeds of 10-20 mph can be expected with gusts
occasional between 20-30 mph.

Midlevel flow will start to buckle from southwest to south Wednesday
night into Thursday as the offshore low continues to dig down the
Pac NW Coast. This will allow warmer midlevel air to surge
northward into Ern WA and N ID and shove whats left of today`s
frontal boundary back to the north and west. Model guidance are in
good agreement of 700-500mb lapse rates climbing 8C/km across a
majority of southeastern WA and N Idaho...and at times expanding
into extreme NE WA. So confidence is moderate to high for midlevel
instability. Next, we look for moisture. Well the remnants of the
current resident moisture plume will be here to stay. It will lose
its connection to the tropics but PWATS along this ribbon will
generally be on the order of 0.75-0.85". So we will have the
moisture and instability but there may be one lacking
ingredient...lift. The best moisture and instability looks to
reside in an area void of any shortwaves or disturbances and this
leads us into a low confidence forecast in regards to
shower/t-storm potential for Wednesday night and Thursday.
NAM/SREF support the idea of thunder for early Thursday morning
and again Thursday afternoon while the GFS/ECMWF/Canadian only
hint at isolated coverage in the mountains with heating of the day
Thursday afternoon. Given the lack of any forcing or shortwaves, I
am leaning toward the later for thunder but did add a slight
chance for sprinkles for Thursday morning in the event, there is a
feature that models may not be picking up on this far out and
potential instability that exists.

Temperatures will remain mild through the period with afternoon highs
in the 70s and lower 80s and overnight lows only cooling into the
40s to 50s. /sb

Thursday night through Tuesday...The deep and tightly wrapped
circulation field in the Gulf of Alaska readily visible on
satellite will increasingly impact the regional weather over the
next week...driving a deterioration into an active and cool fall
pattern for the region.

Models are in pretty good agreement through Saturday in dropping
this deep upper low to a position just off the Washington and
Oregon coast on Thursday and Friday. As it settles into this
position it will promote a sustained period of moist southerly
flow over the forecast area. The unseasonably mild temperatures
currently holding sway over the region will continue through
Friday...albeit cooling a few degrees each day...aided by this
southerly flow. This will set up a period of weakly unstable and
moist conditions over eastern Washington and north Idaho which
will be available for exploitation into isolated to scattered
hit-and-miss showers and possibly thunderstorms for the Thursday
night through Friday evening time frame as weak outridingdisturbances
ride up this flow...with the best chance over the mountains
ringing the basin. This will be a transition period where most
locations will remain dry but with a relatively small risk of
shower or storm each day.

The beginning of the really active weather will arrive Friday
night and into Saturday morning. the GFS and EC models both push a
more focused and better defined wave and cold front through the
forecast area and this event will likely bring the best chance
for precipitation to most locations during this transition period
along with a good ten degree cooling in Saturday`s highs over

From late Saturday onward through the beginning of next week the
models maintain good agreement overall in depicting the inland
ejection of the offshore closed low with high confidence of a much
cooler than average regime...with most locations only achieving
mid 50s to lower 60s as daytime highs...snow levels plunging to
around 5000 feet...and a chance of at least a few showers each day
through Tuesday with occasionally breezy conditions. The models do
differ in the magnitude of precipitation threat...with the EC and
Canadian models forming a split flow with the main dynamic trough
base passing south of the forecast area as it pushes inland...
suggesting a hit-and-miss shower regime with the forecast area under
the northern branch weaker trough...while the GFS throws open the
door to a much more moist and wet pattern for the forecast area
with the season`s first moist frontal complexes and cool season
north Pacific low pressure transiting straight through the
forecast area early next week...with the associated periods of
stratiform rain and mountain snow and potentially downright windy
conditions. In either is probable that any residual
summer-like weather is over until next year after this weekend.


00Z TAFS: A slow moving cold front will sag over the Inland
Northwest through this evening. Strongest winds with the front
are down the Okanogan Valley that will then spill out over the
Waterville Plateau and into the Moses Lake Area. Sustained winds
of around 20 kts are expected at KOMK weakening to around 10 kts
as these winds reach KMWH by 03Z. NE winds will funnel down the
Purcell trench towards morning and increase winds in KCOE toward
12kts. Mostly clear skies will continue for the TAF sites.  JW


Spokane        52  79  53  78  51  74 /   0   0  10  10  20  20
Coeur d`Alene  51  79  53  78  51  73 /   0   0  10  10  30  30
Pullman        52  80  53  78  50  74 /   0   0  10  10  30  20
Lewiston       56  85  58  82  55  78 /   0   0  10  20  20  20
Colville       45  78  48  79  46  75 /   0   0  10  10  20  20
Sandpoint      45  75  49  76  48  71 /   0   0  10  20  30  30
Kellogg        50  79  51  77  49  73 /   0   0  10  20  30  30
Moses Lake     50  80  49  79  46  75 /   0   0   0   0  10  10
Wenatchee      53  78  54  77  50  74 /   0   0   0   0  10  10
Omak           48  78  50  79  48  75 /   0   0   0   0  10  20



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