Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 192014

Area Forecast Discussion
National Weather Service Pocatello ID
114 PM MST Thu Jan 19 2017

.SHORT TERM...Tonight through Saturday night. The current storm
system is moving off to the east this aftn...with only light snow
lingering in the mtns...especially the eastern and southern
highlands where anothe inch or two of snow is possible overnight.
A few mtn snow showers are possible on Fri...with little
accumulation. Another system moves into the Pac NW on Fri...and
begins to spread snow across the fcst area Fri night. This system
is weaker...with most of the moisture going to the south. Only
looking for 1 to 2 inches in the lower elevations and 2 to 4 in
the mtns...before tapering off Sat aftn. Hedges

.LONG TERM...Sunday through Thursday. It appears that our next period
of more significant precipitation will come Sunday into Monday. The
models and ensembles continue to paint a "less than clear" picture
of how this may pan out exactly. This is mainly in terms of detail
and placement of heavier amounts but at least an overall trend is
there. That points to a big chunk of the low off the west coast
spins off and moves inland.  There is some concern that it will try
to turn into a closed low briefly somewhere over Idaho (or close
by). This will slow down the movement obviously and also play havoc
with amounts. Once again, with the flow being from the south and
west ahead of this wave, look for overrunning of any cold air locked
in place. This means some places especially along/south of the Snake
River and I-84/86 could see freezing rain. Those sames areas may
also a period of changeover to actual rain. We tried to not stray
too much from the last forecast update. Heading into Tuesday, we
should see northerly flow kick in bringing dry and colder air in
from Canada. We may have to watch Monday night for a convergence
band dropping south across the Snake Plain based on this pattern.
The models continue to produce light snow outside of the central
mountains. This is likely due to different mechanisms taking place,
but both realistic in this flow. One is under any stratus deck that
forms and the other is upslope flow along the Interstate corridor
and eastern highlands. Keyes


.AVIATION...We continue to watch the main area of rain and snow
shifting east this afternoon. As this happens, we are seeing
improvement in some areas in terms of ceilings and visibility. The
question becomes will conditions become VFR everywhere and remain
that way.  The answer: no.  Are we confident on our forecast of low
stratus, fog and potential for pockets of light precipitation to
form? Not 100%.  We will continue with TAFs that call for a return
to MVFR/IFR conditions, even at KSUN for a period after things clear
out. We do have plenty of moisture out there so that lends itself
for the more pessimistic forecast.  We may end up making sweeping
changes later tonight IF this doesn`t pan out as we currently think
it will.  Keyes



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