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FXUS66 KOTX 201135

Area Forecast Discussion
National Weather Service Spokane WA
435 AM PDT Sun Aug 20 2017

Bands of mid and high clouds are expected to move over the Pacific
Northwest today, but we will see clearing overnight. Skies should
be favorable for viewing the eclipse Monday morning, however 
there may be some smoke in the northern valleys. Tuesday and 
Wednesday will be quite warm with afternoon temperatures in the 
upper 80s to mid 90s. A vigorous cold front on Wednesday night 
will have the potential to produce thunderstorms, with strong 
winds expected on Thursday.


Today through Monday night: A dry northwest flow will continue
today before weak high pressure begins building on Monday. A weak
wave embedded within the northwest flow will track across southern
BC today clipping northern Washington and the north Idaho
Panhandle. Main impact from this will be mid and high level cloud
cover. This wave exits tonight bringing clearing skies. 

For Monday (Eclipse Day), the 00z GFS and ECMWF model progs show 
a band of cirrus moving into Central Washington in the morning 
reaching the Idaho Panhandle during the late morning or early 
afternoon. Satellite imagery shows quite a bit of high clouds to
our west-northwest so this idea is accepted.  This moisture is 
very high up (above 300 mb) and shouldn't have much of an impact 
on eclipse viewing. The other issue of note is smoke and haze 
which moved into NE Washington and the N Idaho Panhandle 
yesterday. Southwest winds this afternoon is expected to improve 
the smoke/haze situation for the Spokane/Coeur d'Alene area but 
isn't expected to bring much improvement to the northern valleys 
and N Idaho Panhandle where lighter winds are expected. 
Still...the smoke/haze isn't as bad as what occurred during the 
first 10 days of August and probably won't have to much of an 
impact on the eclipse. Mostly clear skies and the weak ridge will 
allow for the beginning of a warming trend with highs in the mid 
to upper 80s for most towns with the warmest spots in the lower 
90s. JW

Tuesday and Wednesday: Our forecast for Tuesday and Wednesday has
changed little. The models continue to forecast the amplification
of a broad high pressure ridge on Tuesday leading to above average
temperatures. Tuesday should be our warmest day with high
temperatures in the upper 80s to mid 90s. We will have light 
winds in the lowest 8 to 10 thousand feet of the atmosphere on 
Tuesday under our 500mb ridge. With smoke being produced by fires 
in BC, Oregon, central Idaho, and north central Washington, it may
be tough to escape the haze and smoke. With fires all around, our
only "clean" wind direction is out of the west. On Wednesday, the
500mb ridge axis will migrate into Montana allowing increasing
on-shore flow to bleed a bit of marine air into our region. Look
for our temperatures to be a couple degrees cooler Wednesday
afternoon with afternoon winds of 5 to 15 mph.

Thursday: The evening runs of the GFS, ECMWF, and Canadian models
continue to suggest that Thursday will be our most volatile
weather day of the week. It is still possible that the timing and
intensity of this storm could change, but at this time it looks
like it could be one of our most noteworthy events of the summer.
A vigorous cold front is expected to push through the Inland 
Northwest during the early morning hours.

*Thunderstorms: A ribbon of mid-level moisture and instability is
 forecast along and ahead of the cold front suggesting scattered
 showers and thunderstorms over the Idaho Panhandle and southeast
 Washington early in the day Thursday. Model soundings suggest
 high cloud bases and fast storm motion. It is too early to tell
 how much lightning may accompany storms early on Thursday, but it
 does not appear that fast moving, high-based cells will produce
 much wetting rain. Given the extreme dryness of July and August,
 our fuels are critically dry. Any lightning at this stage is a
 potentially significant wildfire concern.

*Wind: A negatively tilted 500mb trough tracking along the
 Washington/BC border is notorious wind producing pattern. Strong
 cold advection will occur Thursday into Thursday evening. Steep
 lapse rates from the surface to 700mb will allow efficient
 downward momentum transfer from late morning through early
 evening. Fortunately, model winds aren't stronger in the layer
 around 800-850mb (30-35kts), or our gust potential would be
 higher. At this time, it looks like sustained 20 to 25 mph winds
 with gusts of 30 mph or more across the Columbia Basin, Palouse,
 and West Plains from late morning through early evening.
 Localized gusts up to 40 mph will be a good bet through the
 Cascade gaps around Wenatchee, Entiat, Chelan, and Vantage.

*Blowing Dust: The magnitude of the wind and the duration of the
 wind through the afternoon into the evening will heighten the
 risk of blowing dust. We have had little to no measurable
 precipitation across the dryland wheat country since late
 June...leaving the region susceptible to blowing dust.

Friday and Saturday: Temperatures on Friday will be noticeably
cooler in the wake of Thursday's strong front. Much of the Inland
Northwest will only top out in the 70s to around 80. Our temps
will rebound a bit on Saturday...close to seasonal normals. 


12Z TAFS: Main aviation concern will be smoke settling into the 
valleys of NE WA and N ID with the overnight inversions. Overall,
confidence remains low for restrictions at the main terminals but
is MVFR visibilities are possible at Colville, Deer Park, Bonners
Ferry, and Sandpoint. Otherwise...expect generally light winds 
with afternoon gusts around 15 mph. JW


Spokane        81  57  85  61  90  63 /   0   0   0   0   0   0 
Coeur d'Alene  81  53  86  55  91  58 /   0   0   0   0   0   0 
Pullman        79  52  85  54  91  59 /   0   0   0   0   0   0 
Lewiston       87  60  92  62  97  66 /   0   0   0   0   0  10 
Colville       82  51  86  52  91  54 /   0   0   0   0   0   0 
Sandpoint      81  46  84  48  87  51 /   0   0   0   0   0   0 
Kellogg        77  50  84  54  89  55 /   0   0   0   0   0   0 
Moses Lake     86  55  90  57  94  60 /   0   0   0   0   0   0 
Wenatchee      86  62  89  64  93  65 /   0   0   0   0   0   0 
Omak           86  59  90  60  94  62 /   0   0   0   0   0   0 



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