Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 221130

Area Forecast Discussion
National Weather Service Spokane WA
430 AM PDT MON SEP 22 2014

Warmer-than-normal temperatures are expected through at least
Tuesday. A pattern change will occur by mid week, and more early
Autumn-like potentially rainy weather pattern will be common over
the Inland Northwest to finish out the week. A slight warming and
drying trend is expected to occur next weekend.


Today through Tuesday: The Inland Northwest will experience a
pattern change over the next 48 hours as the upper level ridge of
high pressure slowly breaks down by an increasingly moist
southwest flow. The area of high pressure will be be nudged east
today as a weak shortwave ripples up the Cascades this morning.
The weather models indicate a band of light showers to develop
along the Cascade crest this morning, and then propagate east into
Okanogan highlands this afternoon. Meanwhile the upper level low
is exiting Nevada and cutting across southern Idaho. As it does,
mid level moisture will brush across southeast Washington and the
Idaho panhandle. By afternoon, surface based instability will
increase slightly as the cap weakens, and there is the potential
of thunder across the Blue mountains and near the Cascade crest
during the afternoon and early evening hours. Precipitation from
these showers is expected to be little if any especially as the
low levels of the atmosphere remain dry. Temperatures today will
cool a few degrees due to the increase in cloud cover by
afternoon, while light winds become more southwesterly. Monday
night and into Tuesday, the ejecting upper low pushes further east
and releases its grip on southeast Washington, but the moist
southwest flow expands across the region as a Pacific frontal
boundary sweeps in from the southwest. As this weakening frontal
boundary crosses the Cascades by early Tuesday morning, clouds and
a chance of showers will develop across much of eastern
Washington, pushing into north Idaho by Tuesday afternoon. The
southern sections of the boundary will develop into a warm front
that will push north across the region by the afternoon and
evenign hours. Instability will be the best across northeast
Washington and north Idaho by Tuesday afternoon and have indicated
the potential for thunderstorms during the late afternoon and
early evening. Temperatures on Tuesday will cool slightly a couple
more degrees while southwest winds pickup during the afternoon.

Tues nt through Mon: Once the weak warm front lifts north into Srn
BC Tue nt, much of far Ern Wa and all of N Idaho will be in the
warm and dry air mass east of the cold front near the Cascades.
And with the upper trough just off the Pac Nw Coast showing
significant north/south shearing as a speed max digs south down
the back side of the trough, this cold front will move little as
it stalls over the Upper Columbia Basin until midday Thurs. Pcpn
amnts under this narrow frontal band should only be a few
hundreds in the lowest elevations, with around a tenth in the
mtns, including the Cascades. There may be some embedded
convective elements that may produce isolated higher amnts to
around a quarter inch. It`s not until Thurs afternoon that the
first vort max is ejected from the stnry trough and moves through
Oregon and into the Idaho Panhandle that the front shows Ewd
movement and helps to produce scattered showers for much of Ern Wa
and N Idaho. Once this wave moves out of the area, the entire
upper trough translates E and weakens further, putting only SE Wa
and the Camas Prairie of Idaho of linger showers as what`s left of
a subtle deformation axis tries to produce a narrow corridor of
banded pcpn. The Gfs model then strengthens and stalls the upper
low over Srn Idaho as another speed max digs into the base of this
trough, cutting it off from the main belt of the westerlies to the
north. We`ll have to watch closely how model guidance handles this
typically tricky pattern since the ECMWF brings the threat of pcpn
back into SE Wa Sunday from the Nrn periphery of this stalled low.


12Z TAFS: Mid level cloudiness will move up the Cascades with a
few showers possible near KEAT this morning. Otherwise mid to
upper level clouds will span from KLWS and KPUW toward the KGEG-
KCOE cooridor this morning. The arrival of a warm front late
tonight will bring a slight chance of showers to most TAF sites
before 12z Tues. /rfox.


Spokane        83  58  79  57  81  54 /   0  20  20  10  10  10
Coeur d`Alene  83  55  79  55  82  52 /   0  20  20  10  10  10
Pullman        82  55  82  54  84  52 /  10  20  20  10  10  10
Lewiston       87  62  86  60  87  58 /  10  20  20  10   0   0
Colville       85  53  79  53  81  48 /  10  20  30  20  20  20
Sandpoint      80  50  75  50  79  48 /   0  20  30  20  10  10
Kellogg        80  55  78  56  81  50 /   0  20  20  10   0   0
Moses Lake     87  57  81  58  81  54 /  20  10  20  10  20  40
Wenatchee      86  62  79  62  77  58 /  20  10  20  20  30  40
Omak           87  57  79  57  76  52 /  20  20  30  30  40  40



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