Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 281202
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
502 AM PDT Wed Sep 28 2016

.SYNOPSIS...
Mild and dry weather continues today. Breezy winds will diminish
out of the Okanogan Valley this morning. The mild weather will
linger in the area through Thursday before a cooling trend takes
hold of the region. Cool and showery conditions are expected
through the weekend with temperatures 20 degrees cooler than what
the region is experiencing now. Mild and dry weather continues
today. Breezy winds will diminish out of the Okanogan Valley this
morning. The mild weather will linger in the area through Thursday
before a cooling trend takes hold of the region. Cool and showery
conditions are expected through the weekend with temperatures 20
degrees cooler than what the region is experiencing now.

DISCUSSION...
Wednesday through Thursday Morning...

This morning`s water vapor satellite depicts a digging trof off
the PacNW and BC coast. This cold core low continues to drop
almost due south. This feature will drive our sensible weather
through about mid next week. In the short term, an obvious
shortwave is visible on the water vapor imagery nearing the WA
coast. Mid and high level clouds have increased over the past few
hours as moisture pools out ahead of this feature. This shortwave
will shear apart during the day today as it moves over WA and
southern BC. The upper levels will dry out on the western half of
WA while most of our domain will continue to have some scattered
to broken high clouds.

As for sensible weather, the gusty north winds out of the
Okanogan Valley have diminished overnight although still seeing
blustery conditions over the Waterville Plateau. High res models
bring these winds down rapidly during the early morning hours
which is consistent with the ongoing forecast. Minor changes were
made in the first 36 hours to account for increased mid and high
level clouds with the sheared vort max hanging around through
Thursday.

Temperatures will be very similar to Tuesday...although just a
few degrees cooler thanks to the clouds. Rain chances are zero
through Wednesday night. Models indicating increased mid level
instability in our far southeastern zones by Thursday so
introduced some slight wording in the forecast.

Thursday afternoon through Sunday night...Model guidance is in
pretty good agreement through this period. An upper level closed
low currently in the eastern Pacific will continue to drop south
along the coast and finally begin to push inland around the
central Oregon coast on Sunday. Numerous weak disturbances will
move through the low and affect the weather through the weekend.
The models are also consistent in showing a secondary low dumb-
belling around the main low on Saturday and pushing a fairly
robust disturbance through the region on Saturday. Overall we can
expect a chance of showers and possible thunderstorms and much
cooler temperatures.

Thursday night and Friday night...Southerly flow will deepen the
moisture over the the region. Model guidance has been showing
increased mid-level instability for the past couple of runs and
all that was missing to kick off convection Thursday night was a
decent kicker. The 00z runs are now showing a weak wave moving
through eastern Washington Thursday night and this may be enough
to tap into that mid level instability. This will result in a good
chance for showers and the possibility of nocturnal thunderstorms
across the basin and moving northeast into the northern mountains.
Confidence in showers is much higher then for thunderstorms. The
sub cloud base is will start out pretty dry and precipitation
amounts will not be overly impressive with a couple of hundredths
of rain by morning. After a brief break in the showers Friday
morning, surface heating will help to destabilize the atmosphere
and another round of convection is expected for for late in the
afternoon. Temperatures will begin cooling but highs will likely
remain just on the warm side of normal.

Saturday through Sunday...This period will have the best chance
for widespread precipitation. A cold front will make it the
Cascades between 06-12z Saturday and stall along the crest. A
short wave will move north through the forecast area with
widespread showers forming along the wave. This will result in
about a 6-12 hour period of moderate showers. The cold front
finally gets kicked through the region Saturday night with an even
stronger wave moving along the front. While the moisture tap
weakens somewhat on Saturday it should be overcome by the strong
dynamics. Rainfall will be sparse in the basin and lower east
slopes with only a couple of hundredths expected. From a tenth to
around a quarter of an inch will be possible for the remainder of
the area. Temperatures will come tumbling down with the cold front
passage. High temperatures will cool down into the 60s on Saturday
and down to the high 50s to mid 60s on Sunday.

Sunday and Sunday night...The models have been hinting at the
upper level low taking a dive south for a few runs and now it
seems as if they are all on board with a more southerly route.
That in turn will keep the best chances for precipitation to the
south of our area and pops were lowered accordingly. Tobin

Monday through Wednesday: Rather significant drying out from what
the previous model runs have been suggesting for Monday. The
center of the upper low has moves east and a weak and short lived
ridge tries to build in for the Monday-Tuesday timeframe
accompanied by some drier air. This will keep diurnal shower
chances mostly confined to the areas surrounding the basin
through at least mid week. With no upper ridging in sight temps
will remain cool in the upper 50s and low 60s each day. /bwilliams

AVIATION...
12Z TAFS: The pressure gradient that has been driving the breezy
north winds across the region is diminishing. Generally light
winds will prevail at all TAF locations under VFR. The 12Z update
included minor tweaks to the timing of the local winds as well as
increased high level clouds during the day. BKN to OVC high clouds
will prevail for most central and eastern TAF locations during the
day although no precipitation or vis reductions are forecast
for the next 24 hours. Showers and possibly thunderstorms come
back into the picture (especially the ID TAFs) Thursday and
Friday. AB

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        79  53  78  51  73  46 /   0   0  10  30  20  50
Coeur d`Alene  79  52  79  51  73  47 /   0   0  10  30  20  60
Pullman        80  51  79  50  75  44 /   0   0  10  50  10  30
Lewiston       85  58  83  55  79  51 /   0   0  10  20  10  30
Colville       78  47  80  48  74  44 /   0   0  10  20  20  50
Sandpoint      75  48  77  48  71  44 /   0  10  10  30  20  60
Kellogg        79  53  78  50  72  45 /   0  10  20  30  30  40
Moses Lake     82  48  80  50  75  44 /   0   0   0  30  20  10
Wenatchee      78  50  78  51  74  47 /   0   0   0  10  10  10
Omak           78  48  80  49  76  45 /   0   0   0  10  20  10

&&

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

$$


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