Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 200235

Area Forecast Discussion
National Weather Service Boise ID
835 PM MDT Sat Aug 19 2017

.DISCUSSION...Latest models keep our CWA almost completely
cloud-free at eclipse time.  Any clouds in the path of
totality would be in the central Idaho mountains, but even
there no more than 10% coverage.  In the partial-eclipse
area about 10% coverage near the Nevada border, and zero
to 5% elsewhere.  Smoke is currently greatest in southern
and central parts of our CWA, at around 15000 feet MSL.
Less smoke is in northern areas.  West or northwest winds
aloft through Monday may push the smoke a little farther
south making viewing of the eclipse even better.  Otherwise,
current forecast is on track through Monday with clear, dry
weather, and normal temperatures with light winds.


.AVIATION...VFR through Monday. Seeing slight reductions in
visibilites below 15kft MSL due to layers of smoke across southeast
Oregon and southwest Idaho. Surface winds 10 kts or less overnight,
becoming northwest 10 to 20 kts across open terrain Sunday. Winds
aloft through 10kft MSL will be west-northwest 10-20 kts.


SHORT TERM...Tonight through Monday...A dry west/northwest flow
will keep conditions dry and mostly clear through Monday, with
breezy afternoons. A strengthening closed low near the coast of
Southern California is expected to push moisture north on its
eastern side. However, with the low`s placement, much of this
moisture and cloud cover will stay near or south of the Northern
Nevada border through the short term. With week ridging aloft on
Monday, confidence is growing in a drier and clearer forecast.
This means that viewing conditions, in regards to cloud cover,
will be favorable along the path of totality of Monday`s eclipse
in Western Idaho and Eastern Oregon. However, many wildfires
across the region are still putting out smoke. If the existing
fires remain, the flow will be such that most of the smoke will
stay aloft but thinly dispersed over the CWA, so surface and
eclipse visibilities should remain favorable. If new fires start,
the smoke could rapidly become an issue once again, depending on
location. Temperatures should remain near normal through the

LONG TERM...Monday night through Saturday...Period starts off warm
as the upper ridge axis shifts east of the Divide. Southerly flow on
the back side will draw moisture to the Nevada border on Tuesday,
which will support a slight chance of afternoon showers and
thunderstorms. Wednesday and Thursday see an increased chance of
precipitation across the area as the moisture stretches further
northward ahead of an upper trough tracking through southern BC,
Canada. The increased cloud/shower coverage will take a few degrees
off high temperatures those days, with further cooling for Friday
behind the trough passage. Seeing good model agreement with the
development of an upper level ridge returning hot and dry weather to
the area for the weekend.





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