Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 172024 CCA

Area Forecast Discussion
National Weather Service Pocatello ID
123 PM MST Fri Nov 17 2017

.SHORT TERM...Tonight through Monday. Satellite imagery
was showing a low pressure trough working east across SRN Idaho
early this afternoon with clearing skies west of the trough axis and
ongoing snow showers east of the axis. Numerical models all appear
to support the development of a convergent snow band developing
across the upper valley later this afternoon which quickly dies off
early this evening. Thus have maintained a short period of high
probability snowfall across the area (especially the eastern
highlands) early this evening with rapid clearing towards midnight.
Advisory level winds have been a little slow to develop this
afternoon although guidance still supports stronger winds across the
Eastern Magic Valley and Lower Snake River Plain. It may be difficult
to realize those winds across the Upper Snake River Plain especially
if a convergence event is expected to push out of the CNTRL
mountains. Thus have cancelled the advisory for the upper valley. A
modest ridge of high pressure builds across the NW states Saturday
with cool and mostly clear skies across the region. The next Pacific
storm system tops the ridge Sunday night and digs SE into Idaho by
Monday morning with attending snow showers spreading from NW to SE
across the region during the day. This appears to be a fairly
progressive system which should help to limit accumulations. Daytime
temps are expected to run at or slightly above climatic norms
through the period. Huston

.LONG TERM...Monday night through next Friday night. Active period
of weather is expected to persist through the long-term period with
several rounds of Precipitation expected. Monday night, the first
trough of Low Pressure will be exiting the area with Snow Showers
lingering over the Eastern Highlands along the Wyoming border as
well as along the Southern Highlands along the Utah border, possibly
resulting in some difficult travel. A weak Ridge of High Pressure
this then forecast to briefly build into the area on Tuesday, with
the only lingering Snow Showers likely limited to the Island Park
region. Will have to monitor for the potential for low clouds in the
valleys and especially the Snake Plain that might hold high
temperatures down, otherwise a warming trend should begin Tuesday
commensurate with the weak Ridge. The next round of precipitation is
forecast to build into the Sawtooths/Pashimeroi eastward along the
Divide to Island Park on Wednesday, with models now showing this
activity remaining west of the area on Thursday as the Ridge
strengthens. Through Thanksgiving, Snow Levels will be high in the
presence of temperatures that may range 19-15 degrees above
climatological averages Wednesday and Thanksgiving Day. The Ridge is
expected to begin to weaken on Friday, sending another wave of
Precipitation across the area, along with a cooldown. With a busy
travel week and several bouts of Precipitation expected to impact
the region, continue to monitor the latest forecasts for any large
changes in potential impacts to travel. AD/Huston

.AVIATION...Cold front sweeping through at this time creating all
sorts of problems, not only with CIGs, but also VSBYs and wind.
Snake River plain wind just now increasing to 25kt territory at
KPIH, but should be the only airdrome with those kind of speeds,
what is more difficult will be direction at KSUN and KDIJ. A
secondary line of showers is coming out of the upper Snake River
highlands and should affect KDIJ shortly, bringing CIG/VSBY down to
near closure levels. KIDA could also be affected by this feature.
KBYI appears stuck with marginal VFR CIG, and occasionally getting
to IFR. KSUN is behind the front and has already scattered out with
only the expected gusty wind to be a forecast issue. All airports
should be trending upward with only two exceptions. KDIJ and KIDA
are the locations most likely to have stratus problems in the
morning. The forecast boundary layer moisture is too dry for KBYI
and KPIH at this time and wind is staying up in magnitude enough to
prevent fog from being a factor. Boundary layer moisture is expected
to be high for both KDIJ and KIDA, and the elevated wind favors
stratus over fog. But headaches due to wide-ranging VSBY and CIG
likely to continue into the late afternoon/early evening tonight.

Wind Advisory until 8 PM MST this evening for IDZ017-021.

Winter Weather Advisory until 8 PM MST this evening for IDZ019-023-

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