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FXUS66 KOTX 200522

Area Forecast Discussion
National Weather Service Spokane WA
1022 PM PDT FRI SEP 19 2014

Strong high pressure will provide a generally clear...warm and
dry weekend for the Inland Northwest. The new work week will start
out with continued above normal temperatures but a weak cold front
will bring a chance of showers starting Tuesday. From mid-week
onward an approaching deep trough will increase the probability of
rain with cooler temperatures.


Tonight through Sunday...An upper level ridge is beginning to
build over the region this afternoon. Satellite suggest one last
weak disturbance transiting the northern reaches of the forecast
area but this wave will bring little more than some clouds near
the Canadian border this evening before a general clearing trend
commences in earnest.

All model guidance is in good agreement in building and
maintaining this ridge through the weekend. Surface high pressure
off the coast currently will shift into southern Canada tonight
and then into the Canadian Prairie and Great Plains by
Sunday...promoting northerly and eventually northeasterly winds
across the forecast area. This flow will bring dry continental air
into the region and with subsidence aloft under the ridge after
tonight very little in the way of clouds...let alone
precipitation...will be apparent.

Plenty of sunshine into a dry near surface air mass will allow
efficient diurnal heating leading to increasing temperatures each
day...topping out by Sunday a good 10 to 12 degrees above normal.

Sunday night through Wednesday...Ridge of high pressure continues
to amplify while the axis of the ridge migrates east from
Northwest Montana. The ridge axis is well to the east over Eastern
Montana Monday and the southerly/southwesterly flow to the east of
the axis will allow for forecast temperatures to likely mirror
those expected on Sunday. Monday afternoon through Tuesday models
suggest a few weak disturbances with limited moisture and
instability will run up the west side of the ridge and produce
some convection. A robust 0-6km southwest to northeast wind of 25
mph along with fairly dry lower levels of the atmosphere favor
virga more than rain which allows for fairly low pops and coverage
for showers Monday afternoon through Tuesday. Tuesday night but
primarily Wednesday a large occluded frontal zone that has a well
maintained south to north orientation and tap into subtropical
moisture moves through which allows for a substantial increase in
pops and wind and significant cooling apparent in the cooler
daytime highs forecast for Wednesday for the western half of the
forecast area while the eastern portion may remain steady or warm
a degree or two as the warmer southerly flow ahead of the incoming
frontal zone and onset of rain late in the day allows for it..

Wednesday night through Friday: A broad upper-level trough will
translate from the Ern Pac into the Wrn US during this time-frame
delivering cooler temperatures and increasing threat for
precipitation. All model guidance is on board with the upcoming
changes however timing and precipitation amounts continues to
carry moderate uncertainty. There is strong agreement that the
leading cold front will cross the Cascades around Wednesday night
with a nice fetch of three quarters to an inch of precipitable
water. How fast this translates east is the question. A strong jet
digging down the backside of the trof will slow the trof down then
flow on the leading edge looks to eventually parallel the front or
become southerly. This favors a slowly trickling west to east
frontal passage with abundant moisture but weak ascent. Some
models are tracking smaller disturbance along the front which is
highly possible and would lead to increase precipitation amounts
perhaps near a quarter of an inch but whether this occurs over the
Wrn Columbia Basin or in the Idaho Panhandle cannot be determined
at this time. Needless to say, a weather pattern change is in
store which will end the warm and dry conditions expected to start
the week. Temperatures will generally remain mild for overnight
lows with abundant cloud cover in the region. High temperatures
will generally remain steady and near seasonal readings (upper
60`s to mid 70`s) as 850mb temperatures range between 10-13
Celsius. /sb


06Z TAFS: High pressure will promote dry and VFR conditions at
TAF sites, with light diurnal winds. Some patchy fog is forecast
for the sheltered mountain valleys over NE WA and north ID late
overnight and Saturday morning (09-18Z). At this time it is
expected to remain away from TAF sites. /J. Cote`


Spokane        51  81  52  85  56  84 /   0   0   0   0   0   0
Coeur d`Alene  49  80  49  85  53  84 /   0   0   0   0   0   0
Pullman        47  83  49  88  52  85 /   0   0   0   0   0   0
Lewiston       55  87  56  91  59  89 /   0   0   0   0   0   0
Colville       46  84  47  87  47  86 /   0   0   0   0   0   0
Sandpoint      43  77  44  81  45  79 /  10   0   0   0   0   0
Kellogg        49  78  48  83  52  81 /   0   0   0   0   0   0
Moses Lake     50  86  54  89  56  89 /   0   0   0   0   0   0
Wenatchee      56  85  58  88  61  87 /   0   0   0   0   0  10
Omak           49  85  50  89  54  87 /   0   0   0   0   0   0




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