Area Forecast Discussion
Issued by NWS Spokane, WA

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315
FXUS66 KOTX 232109
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
209 PM PDT Wed Aug 23 2017

.SYNOPSIS...
A cold front will bring a threat for showers and isolated
thunderstorms tonight into early Thursday mainly over the eastern
third of Washington and the Idaho Panhandle. This will be followed
by gusty westerly winds Thursday. After cooler weather Thursday
and Friday, the heat will return for the weekend and early next
week.

&&

.DISCUSSION...
Tonight through Friday...The weather will become increasingly
active over the next 24 hours...and then die down back to a high
summer warming and drying trend. Satellite indicates a slug of
monsoonal moisture originating over Oregon and being drawn
northward into eastern Washington and north Idaho this
afternoon...drawn in the southwest flow ahead of an incoming
offshore trough. This moisture...while mainly manifesting itself
as mid level clouds with some virga this afternoon...will deepen
significantly overnight and interact with a rather potent but
compact short wave riding up ahead of the main trough. Thus the
stage may be set for an end to the current dry streak at Spokane
International(55 days without measurable precip) overnight tonight
as showers develop east of a line from about Republic to
Ritzville. These showers will be hit-and-miss but scattered rather
than isolated...and they may form in a train over a few locations
late tonight and early Thursday morning in extreme eastern
Washington and more likely north Idaho. All the latest models
indicate the suspect wave developing over this region...so pops
have been increased to high chance and low likelies over the
eastern zones.

The thunder threat tonight in this area looks only marginal.
Instability is limited and weak but the dynamic support from jet
divergence and deferential vorticity ahead of the wave may be
sufficient to trigger one or two thunderstorms salted among the
showers. The limited thunder potential and likelihood of
increasingly wet cells precludes considering a Red Flag Warning
for this element.

The western zones will remain to the west of any of this activity
for partly cloudy conditions and the usual breezy evening gap
winds. Local smoke issues will remain mainly in the vicinity of
active fires but it looks like most of the Oregon smoke is being
shunted off to the east this afternoon.

On Thursday the threat will turn to widespread breezy and gusty
conditions. Residual morning panhandle shower activity will
quickly move off to the east into Montana. The actual Pacific cold
front will cross the Cascades late tonight...and the post frontal
winds will manifest themselves over the entire region during the
day Thursday. Temperatures Thursday will be noticeably cooler than
recent days...however the incoming air mass will be bone dry
making for continued low minimum RH and correspondingly high fire
spread danger. Breezy and gusty is a near certainty in the basin
on Thursday...but the only zone that will confidently reach
critical RH during these winds will be the Wenatchee area...thus a
Red Flag warning will be issued for tomorrow afternoon and early
evening. Otherwise if will be a dry and mostly sunny day with
no smoke issues.

Thursday night and Friday...Things will settle down during this
period as winds taper off Thursday night and become light on
Friday. The cooler air mass will keep temperatures Friday to near
or slightly below normal with continued clear skies. /Fugazzi

Friday night through Wednesday: A zonal flow amplifies into high
pressure ridging through this time interval. This will result in a
warming trend through the interval with temperatures again running
well above average. The forecast could run generally dry until about
Monday on into Wednesday when some of the models suggest a
disturbances running up in the southerly flow underneath the ridge
could fire off convection over extreme Eastern Washington and North
Idaho. So far the GFS is the more aggressive with the depiction of
these disturbance passages while the more favored ECMWF is the least
aggressive their passage. With this in mind for now will perhaps
show more cloud cover at times in the Monday through Wednesday grids
coming up into Eastern Washington and North Idaho with this
southwest to northwest trajectory of approach/exit rather than
increase pops and mention convection. /Pelatti

&&

.AVIATION...

18Z TAFS: smoke from Oregon will continue to stream over Washington
and Idaho, with the highest concentrations in southern Washington.
Mid and high clouds will move in from the south and thicken through
the day. Tonight the chance for showers, with some chances of
thunderstorms, will increase over the eastern third of Washington
and north Idaho as a cold front moves through the region. /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        64  81  52  79 /  50  20   0   0
Coeur d`Alene  60  81  50  78 /  60  40   0   0
Pullman        59  80  47  78 /  60  30   0   0
Lewiston       66  89  56  84 /  40  30   0   0
Colville       55  85  46  82 /  30  10   0   0
Sandpoint      53  81  43  77 /  50  50   0   0
Kellogg        55  77  49  76 /  50  60   0   0
Moses Lake     59  85  48  82 /  10   0   0   0
Wenatchee      64  84  54  83 /  10   0   0   0
Omak           60  85  52  84 /  10   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Red Flag Warning from 2 PM to 8 PM PDT Thursday for East
     Washington Central Cascade Valleys (Zone 677).

&&

$$



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