Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 210520
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1020 PM PDT SAT SEP 20 2014

.SYNOPSIS...
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 Monday night. From
mid-week onward an approaching deep trough will increase the
probability of rain with cooler temperatures.

&&

.DISCUSSION...

Tonight through Monday...High pressure amplifies over the area
with the ridge axis migrating east into Western Montana Sunday
which allows for a continued dry forecast with a warming trend. A
weak cold front rides up the west side of the ridge Monday into
Monday night which allows for cooler temperatures, an increase in
cloud cover, slight increase in wind, and minor pops for hit and
miss showers primarily near the East Slopes of the Northern
Cascades and the Northern Canadian Border. Forecast temperatures
given the ridge remain on the warm side of what would be
considered normal for this time of year. /Pelatti

Monday night through Saturday...The latest medium range models
are in good agreement in depicting the slow approach and eventual
arrival of a deep Pacific trough into the region through this
period. Thus there is high confidence of a general deterioration
from the dry and warm ridgy weather pattern of this weekend.
Uncertainty exists...and this uncertainty is
considerable...regarding just how quick and how stark this
deterioration into an autumnal showery or even downright wet and
cool period will evolve. The problem concerns not the approach of
the trough...but the exact placement and timing of the main trough
baroclinic region which will likely feature widespread showers
along a relatively narrow and slow moving band bisecting the
forecast area from south to north...or if the GFS pans out a
strong and wet deformation band on or about Friday.

Where better agreement exists...not surprisingly in the earlier
periods of Monday night through Tuesday...a weak outriding
disturbance will bring the potential for isolated to scattered
showers or even a thunderstorm or two on Monday night and Tuesday
morning and begin a slow cooling trend as the surface thermal axis
is shifted eastward into Montana. Tuesday looks like a cloudy but
essentially dry day except near the Cascades as a weak short wave
ridge in the wake of this outriding disturbance rebounds over the
forecast area.

Wednesday and beyond the GFS and ECMWF differ in timing and
eastward progression of a stronger moisture axis and enhancement
along the main trough baroclinic band. The Cascades and deep basin
will probably face the main impact from these showers while the
eastern half of the forecast area may remain dry through
Wednesday. the GFS model supports this prospect...while the ECMWF
model pushes the potential rain band eastward across the region
suggesting a very real threat of showers over the whole forecast
area on Wednesday.

The overall model agreement depicting a highly meridional trough
off the coast meteorologically supports the slower GFS
solution...so the forecast for the eastern basin and Idaho
Panhandle will remain essentially dry for Wednesday and feature
only a slight chance of showers and thunderstorms on Thursday.

Friday and Saturday...On one or both of these days it is
increasingly probable that the trough will finally settle into the
forecast area with significantly increased chance of rain...cooler
temperatures and possibly breezy winds in a generally unsettled
fall pattern. The main uncertainty is whether this trough arrival
will feature scattered to widespread but still hit-and-miss
showers or at least some areas of more long-running stratiform
light rain. /Fugazzi

&&

.AVIATION...
06Z TAFS: High pressure will promote dry and VFR conditions at
TAF sites, with light diurnal winds. /J. Cote`


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        54  87  56  84  58  83 /   0   0   0   0  10  10
Coeur d`Alene  52  86  52  84  55  82 /   0   0   0   0  20  10
Pullman        50  88  51  85  55  84 /   0   0   0   0  20  10
Lewiston       57  91  60  89  61  88 /   0   0   0   0  20  10
Colville       49  87  48  86  52  84 /   0   0   0  10  20  10
Sandpoint      47  82  45  79  50  78 /   0   0   0   0  20  20
Kellogg        52  84  53  81  55  80 /   0   0   0   0  20  20
Moses Lake     54  90  55  89  56  87 /   0   0   0   0  10  10
Wenatchee      61  90  63  87  61  85 /   0   0   0  10  10  10
Omak           52  91  55  87  56  85 /   0   0   0  10  10  10

&&

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

$$



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