Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 170932

Area Forecast Discussion
National Weather Service Pocatello ID
232 AM MST Fri Jan 17 2020

.SHORT TERM...Today through Sunday night. Upper trough sweeping
inland early this morning with leading edge of attending
precipitation already impacting the CNTRL mounains. Models show the
trough advancing quickly east through SRN Idaho this morning and
into WRN Wyoming during the afternoon hours. We should see a very
quick burst of snowfall during the morning commute shifting into the
ERN mountains late in the morning and gradually tapering off this
evening as a shallow/flat ridge of high pressure builds into the NW
states late tonight. Strong gusty winds will accompany the trough
passage today with blowing and drifting snow likely to be the main
issue for most of SE Idaho through the day and into the evening
hours. Fully expect the winds to taper off fairly rapidly after 8 PM
MST. No changes at this time to the going Advisories and Warnings.
The flat ridge shifts eastward into Idaho Saturday as Pacific
moisture works over the ridge supporting scattered light snowfall
across the CNTRL and NE mountains through the day. The ridge begins
to amplify/strengthen Saturday night into Sunday as the next
upstream storm system works closer to the coast all of which
supports drier conditions for SE Idaho through Sunday night. Huston

.LONG TERM...Monday through next Friday. A ridge of high pressure is
forecast to be directly overhead SE Idaho on Monday, providing a
period of dry weather. This ridge will also force the development of
strong near-surface temperate inversions, and as such have once
again shaved a few degrees off of the National Blend of Models
solution in valleys, as it tends to show a warm bias in these
instances, particularly in the presence of snow cover. The ridge is
then forecast to retreat to the east by Tuesday, as a warm front
glides northeastward across the region. Light snow showers in the
Island Park area are favored to develop in this pattern by late in
the day Tuesday. A trough of low pressure and associated cold front
remains on track to slide through the area on Wednesday, providing
the opportunity for a round of snow showers and breezy conditions.
Forecast certainty then diminishes for Thursday and Friday as models
diverge significantly, with some indicating the arrival of another
through while others show the opposite. The National Blend of Models
was left unadjusted, and it offers a reasonable compromise by
indicating the potential for mainly mountain snow showers during
this period along with seasonable temperatures. A more clear picture
of this time period will hopefully emerge in the coming days. AD

.AVIATION...A trough of low pressure and attendant surface cold
front is currently marching eastward through the region. Given the
faster than anticipated movement of the surface boundary and its
forcing low-level winds to back to the SW, wind shear issues have
ended across the region. A band of snowfall is breaking out in
association with the trough dynamics and is generally unfolding as
expected. The bulk of the snowfall after 12Z will occur at KDIJ, and
lingering SHSN should cease here around 18Z. For KBYI, KPIH and
KIDA, breezy W (KBYI) to SW KPIH and KIDA) winds will be in place,
with 20-30kt winds through 00Z. This will lead to areas of BLSN,
particularly at KIDA where the character of the snowpack here will
make it more susceptible to vertical transport by the winds. In
addition, MVFR to IFR stratus will be possible at these 3 sites
through about 18Z. Winds will diminish under 12kt around 03Z for
these locations. At KSUN, the typical diurnal, upvalley wind flow
may be overridden by the passage of the trough, and for this reason
we`re carrying down-valley flow through the day, although confidence
is medium at best in the wind direction forecast here. After 18Z,
odds favor VFR conditions at all TAF sites outside of the possible
pesky patch of Stratus. AD

Winter Weather Advisory until 11 PM MST this evening for

Winter Storm Warning until 11 PM MST this evening for IDZ060.

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