Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 302127
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
227 PM PDT Tue Aug 30 2016

.SYNOPSIS...
The warm late summer weather will come to an end of the work week as
a slow moving weather system arrives. Expect cooler and showery
weather starting Thursday night into Friday, and then lingering
into much of the weekend. Drier and slightly warmer weather is
forecast for early next week.

&&

.DISCUSSION...

Tonight through Wednesday night: A trof of low pressure will
begin to slowly make its move inland bringing an increasing risk
for showers and t-storms and continued trend of cooling
temperatures. For tonight, the focus will be on a compact
shortwave moving up its eastern flank from Oregon into Ern WA and
N ID. Rainfall associated with this feature will very light and
lightning will also be extremely isolated. As of 2PM...there have
only been a few strikes around Medford, OR near the center of the
shortwave and given the thermodynamic profiles, I don`t believe
there will be a lot upon moving through this area. Of bigger
concern will be wind gusts as the rainfall falls into a very dry
subcloud layer. These will not be damaging winds but will have the
potential to briefly blow upwards of 20-40 mph under cells which
can produce slightly heavier precipitation or rain-cooled air.
This system will depart to the north around midnight and a dry
slot will bring clearing skies and dry conditions.

Wednesday and Wednesday night: A majority of Ern WA and N Idaho will
be dry under clear to partly clear skies. South to southwest winds
will steadily increase through the day topping out between 10-15
mph for the afternoon hours. It will be a different story for the
Cascades which will see increasing clouds and chance for showers
and thunderstorms with the approach of a slow moving cold front.
Upwards of a quarter of an inch will be possible along the
immediate crest. The chance for showers will extend as far east of
a line from Oroville to Chelan to Leavenworth but most locations
away from the crest will carry low probabilities for wetting rains
(> 0.10"). /sb

Thursday through Sunday: Looks like a cooler and showery weather
pattern will be over the Inland NW for the holiday weekend. An
upper level low that has been churning off the BC coast, will push
its way inland late Thursday. A moist southwest flow over the
Inland NW will be enhanced by a shortwave rotating around the low
center and pivoting into southeast Washington. This will lead to a
swath of precipitation across extreme eastern Washington and north
Idaho late Thursday night into Friday. Could see some locally
heavy amounts, in the range of 0.2" to 0.4" in 12 hours.
Instability looks weak so want an lightning with this convective
band, but it`s worth monitoring. The track and it speed to exit
the area is skewed by the model differences, especially between
the faster ecmwf and the slower gfs. The trend is for the shower
activity to decrease across southeast Washington and then more
showers developing across the northern zones as the upper level
low moves east of the Cascades Friday afternoon into early
Saturday. This would give drier although slightly breezy weather
across the Columbia Basin and southeast Washington for Friday
afternoon and into Friday night. Models will continue to diverge
for the weekend with strength and track of the low, but theme is
consistent. A broad trough will remain. For Saturday and Sunday,
the upper level trough will be over the region with the best
chances of showers and even thunderstorms across the northern and
panhandle mountains. The more notable weather will be
temperatures. The cool down will start on Thursday with afternoon
temperatures lowering into the 70s. Then by Friday and through the
weekend, expect daytime temperatures in the 60s to lower 70s, some
10 degrees or more below normal for early September. Overnight
lows will be mainly in the 40s, although some of the sheltered
valleys that do experience clearing skies, could dip into the 30s
for overnight lows. /rfox.

Sunday night through Tuesday... Models agree with the
continuation of overall trough pattern, but disagree beyond that.
Operational GFS is more aggressive with another closed low
sliding to our south Monday, which is somewhat supported by its
ensemble mean. The ECMWF is less excited, with more of an open
wave and disturbance running through it. Raised precip chances
some over previous forecast but edged the forecast more toward
the EC for now. However if GFS verifies, the Sunday night into
early Labor Day could be somewhat of an unpleasant one. Beyond
that, temperatures will remain on the cool side, with highs
generally in the low 70s. /Kalin

&&

.AVIATION...
18Z TAFS: Mid and high level clouds will spread across all
terminals today and depart tonight. An accompanying shortwave will
supply lift to squeeze out light showers and a few lightning
strikes. Best chance for lightning will be across NE WA and N ID.
The air mass below will be very dry and any shower or t-storm
activity will present the risk for brief gusty winds and this
should be the main aviation focus outside lightning strikes.
Expect this activity to cross KPUW/KLWS 3-5PM...KGEG-KCOE
5-8PM...and depart arnd 11PM. High based showers will track vcnty
KEAT/KMWH 4PM-7PM. /sb

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        58  82  56  73  51  66 /  20  10  10  10  50  60
Coeur d`Alene  56  81  54  73  50  61 /  30  10  10  10  50  60
Pullman        52  81  52  73  48  65 /  20  10  10  10  50  70
Lewiston       60  87  58  80  55  72 /  20  10   0  10  50  70
Colville       52  84  53  75  47  67 /  30  10  10   0  50  50
Sandpoint      52  80  52  73  47  60 /  30  10  10  10  50  70
Kellogg        53  80  51  72  48  60 /  30  10  10  10  40  60
Moses Lake     55  84  54  77  51  72 /  10  10   0   0  10  20
Wenatchee      61  81  55  73  54  70 /  10  10  10  10  20  30
Omak           56  85  52  76  50  72 /  20  10  10  10  20  40

&&

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

$$



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