Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 232138
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
238 PM MST Fri Feb 23 2018

.SHORT TERM...Tonight through Mon afternoon. Lingering effects of
the weak storm will wrap up in the southeast corner of the
forecast area tonight, right on the heels of a stronger and more
significant storm arriving late tonight and this morning. The
trend for snowfall amounts has been downward, even though the PoP
has increased substantially. So, combined with ridge and Snake
River plain/eastern Magic Valley winds of 20 to 30 mph, have
decided that a Winter Weather Advisory bets suits the situation.
Travel should be difficult, but not expected to be impossible. For
the mountains, only exposed ridges will receive the wind, so
focused more on where the snowfall would exceed 6 inches. There is
a very brief break on Sun, perhaps part of Sun night, before yet
another storm strikes the Gem State. This one should have much
more snowfall, with some rain at the lower elevation possible.
Messick

.LONG TERM...Mon night Through Next Saturday Morning. Snow
associated with Monday`s winter storm will linger for the first
half of Tues, especially in the higher elevations of the Central
Mntns east of Challis/Mackay, the Upper Snake Highlands, WY border
zone, Caribou Highlands, Bear Lake region, and southern
Highlands. Another 1-2 inches will be possible in these areas,
greatest above 6,000 feet. Snow showers at lower elevations should
only result in a dusting of new snow. We dry out Tues
afternoon/eve. Winds by this time should be fairly light, so
gradually improving travel conditions can be expected throughout
the day depending on how snow removal efforts go. Good model
agreement continues for yet another day on progression of the
trough axis and on precip amounts, so forecast confidence is high
through Tues night.

Wed-Thur morning, the long-term models diverge. The GFS pushes a
weak disturbance with decent moisture through our forecast area. The
12Z ECMWF trended a bit closer to the GFS compared to the 00Z run,
which had more of a drier, ridging signature, but it`s still much
drier. The Canadian is also drier with a more pronounced ridging
signature. Took the middle road and blended the GFS/EC with the NBM
and WPC guidance, giving the entire region a low 15-30% chance of
snow showers, highest in the mntns. Forecast confidence is low, but
none of the models are indicating anything high-impact for now.

Thurs, the models depict a closed low pressure system approaching
the Pacific Coast, spreading a significant amount of moisture across
the area Thurs afternoon-Sat AM. There are differences between the
models in the placement of the low. For now, have increased PoPs
during this period, although still undercut some of guidance until
we get a feel for how the models are trending. A slow warming trend
appears in the works for Wed-Thurs-Fri, although we remain just cold
enough to support snow just about everywhere. - KSmith/Messick

.AVIATION...
It`s been a rough morning trying to evaluate/forecast snow activity
at KPIH/KBYI/KDIJ when radar returns are light to non-existent and
the high-res short term model guidance thinks it`s dry. Light snow
continues at KPIH with vsbys down to IFR 1.5-2 SM, and only ended
recently at KBYI. KPIH/KBYI/KIDA continue to deal with MVFR ceilings
less than 2,000 feet as well, which is lingering a bit longer than
model guidance seemed to suggest. Could very well see 2,000 to 3,000
foot cigs continue for the rest of the afternoon at these terminals,
although very dry air and subsidence is moving in aloft, and precip
should be harder and harder to come by. Forecast confidence remains
low, and additional TAF amendments are possible. KSUN and KDIJ are
currently VFR, and should remain so through early Sat morning.

Sat morning TAF groups reflect lowering/thickening cigs trending VFR
to MVFR and increasing winds ahead of our approaching winter storm.
By late AM/early afternoon, MVFR to IFR conditions will be likely
with periods of snow at all terminals. - KSmith/Messick

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to 6 AM MST Sunday
for IDZ017>023-025-031.

&&

$$



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