Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 201955
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
155 PM MDT Sun Aug 20 2017

.SHORT TERM...Tonight and Monday...a weak weather disturbance
that we have advertised for several days is showing up with it`s
associated mid and high level clouds on the IR Satellite imagery
this afternoon pushing through the Northwest. Several different
ensemble runs show a variety of trends as it moves over central
and eastern Idaho overnight. Current forecast show some lingering
high cirrus as the time of the Eclipse tomorrow, but most areas
should be able to view without problems. Current bigger concern is
the potential for smoke to enter a large portion of our area from
fires in the north central Idaho mountains as well a large
portion of Montana. We have added areas of smoke from the central
Idaho mountains over towards Island Park. Central mountains may
have this smoke settle into the Valleys with inversions setting
up overnight while the Snake River Plain will see this smoke
elevated. Problem is with the Eclipse starting around 10 am, will
there be enough mixing in some of the mountain valleys to help mix
the layer before the totality around 1130 am.

No other weather impacts anticipated for tomorrow.

vp

.LONG TERM...Tuesday through Sunday. Short lived high pressure
will give way to the low pressure off the coast of California
when it opens up and moves northeast phasing with an upper scale
trough of low pressure moving into the northwest. A chance of
thunderstorms starts late Tuesday along the Idaho-Utah border
while better chances for impacts are on Wednesday afternoon and
Thursday. There may be a possibility for stronger storms these
two days depending on the timing of the frontal boundary. The
showers should end Friday morning with a large scale ridge of high
pressure taking hold of the entire western US which should
increase our temperatures to above normal along with below normal
precipitation chances.

vp


&&

.AVIATION...VFR conditions expected through the period. Gusty winds
through about sunset, particularly at BYI, IDA and PIH with gusts to
about 20kt from the west-southwest, with the strongest winds at PIH
and IDA. Winds diminish around sunset with little surface wind
increase tomorrow. However, in the morning hours, winds increase to
near 35kt around 7000 ft AGL. Band of cirrus moves through SE Idaho
this evening and overnight before gradually diminishing/moving out
of the area late Monday morning. As flow turns more westerly at
about 15kft-25kft Monday morning, additional smoke from Montana
wildfires may impact VIS/CIG at KSUN and KDIJ, but should still
remain VFR. Most smoke should mix out by late morning.

AD/VP

&&

.FIRE WEATHER...Westerly flow will remain in place this evening
before trending more northwesterly on Monday. Red Flag Warning in
Effect until 9PM this evening for Fire Weather Zones 410 and 425,
with emphasis on the Arco Desert where minimum RH will slide into
the 9-15% range along with wind gusts 25-30 mph. Gusty winds also
anticipated across southern sections of 422 and 476. Will see gusty
winds translate to mid and upper slopes tonight into Monday morning
across 427 and 413 along with minimal humidity recovery above the
thermal belts. Breeziness continues Monday across these zones.
Minimum RH values remain very dry area-wide Mon-Tue. The next chance
for impactful fire weather conditions begins late Tuesday into
Wednesday as a wave of low pressure swings through the northern
Great Basin. Isolated thunderstorms are slated to begin first
Tuesday evening near the UT border then gradually spread north. By
late Wednesday, scattered thunderstorms are possible. For this reason
the GACC has elevated much of SE Idaho fire high risk Wednesday due
to lightning. An approaching Pacific low will keep the thunderstorm
threat going through Friday before a potentially strong ridge of
high pressure begins to build in for the weekend.

AD/VP

&&



.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for IDZ410-425.

&&

$$


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