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Area forecast discussion 
National Weather Service Spokane Washington
1057 am PDT Monday Sep 22 2014

Synopsis...
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.

&&

Discussion...
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
evening 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.
/Rfox.

Tues nt through Mon: once the weak warm front lifts north into srn
British Columbia Tue nt, much of far ern WA and all of north 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 north Idaho. Once this wave moves out of the area, the entire
upper trough translates east and weakens further, putting only southeast 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 European model (ecmwf) brings the threat of pcpn
back into southeast WA Sunday from the nrn periphery of this stalled low.
Bz

&&

Aviation...
18z tafs: a pair of weather disturbances will track across the
region through 18z Tuesday. Ceilings are expected to remain VFR with
most of the moisture confined to between 10k-20k feet mean sea level. A
narrow line of showers over the Cascades will move track slowly
east today towards kmwh through this afternoon. Another band of
showers with isolated thunderstorms with the next wave is expected
to develop over NE Oregon this afternoon...tracking into southeast
Washington this evening and then into NE Washington/north Idaho
overnight into Tuesday morning. Isolated thunderstorms are
possible near klws this evening otherwise thunderstorms are not
expected at the taf sites. Jw

&&

Preliminary point temps/pops...
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

&&

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

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