Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 182055
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
155 PM MST Wed Jan 18 2017

.SHORT TERM...Tonight through Friday. A strong Pac storm system
moving into the west today will spread significant snowfall across
much of the fcst area tonight and Thu. Snow is expected to become
heavy overnight across the central mtns...eastern Magic
Valley...and southern highlands. Some freezing rain is also
possible late tonight and Thu morn in the Magic Valley and
southern highlands. The snow will continue into Thu eve...
accumulating from 8 to 12 inches in western Custer and Blaine
Counties...and 4 to 8 inches in the Magic Valley and southern
highlands. Up to 10 inches may pile up in the northern parts of
the Magic Valley. Snow across the rest of the area is expected to
range from 2 to 4 inches...prompting a winter weather advisory for
the Snake River Plain. There could be a brief period of freezing
rain The morn in the Snake Plain...but models suggesting the warm
layer above the sfc will quickly cool when precip starts.

Snow diminishes in coverage Thu night and Fri...but another weaker
system is expected to bring in a round of light snow beginning Fri
night. Hedges

.LONG TERM...Sat through next Wed night. A very weak 500mb longwave
pattern persists with the upper level ridge transitioning to a
trough after Mon. The ridge is not strong enough to overcome a
vigorous shortwave that breaks it down for Sun afternoon through Mon
afternoon. This is the most significant storm of the period, with a
potential for light to moderate snowfalls, which could rate an
Advisory. It will also be breezy, but no major wind event. There
should be some partial afternoon melting at least during the first
half of this time. After this storm passes, there are now some
differences between the GFS and ECMWF, especially in how cold it
will get for Mon and Tue. The other main difference is where the
best chance for precipitation will be. The ECMWF appears to be
verifying better at this point, so mainly went with it, then
tweaking it towards the GFS. Messick

&&

.AVIATION...Gradual deterioration of CIG and VSBY expected this
afternoon and evening. KSUN will have difficulty staying above field
minimums by early this evening. KBYI will be hampered by -FZRA
around the same time. It will take a while for the precipitation
shield to spread farther east, but by 19/12Z KPIH and KIDA will be
snowing.  KDIJ will be the last at around 19/15Z. With the snowfall
comes at a minimum marginal VFR and all of the airdromes will
eventually get to IFR. KSUN should be closed due to weather for much
of Thursday. Freezing rain will end in KBYI overnight tonight,
changing to all snow. Messick

&&

.HYDROLOGY...We have converted the Flood Warning for eastern
Custer County in central Idaho and central Butte County in
southeastern Idaho to a Flood Advisory, until 1030 AM this Friday,
based on coordination with on-scene emergency management officials.

The Flood Advisory for the town of Challis also continues until the
same time. This was also based on coordination.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM to 9 PM MST Thursday for
IDZ020-021.

Winter Storm Warning until 9 PM MST Thursday for IDZ017-022.

Winter Storm Warning until 9 PM MST Thursday for IDZ018-031.

&&

$$



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