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Area forecast discussion
National Weather Service Pocatello Idaho
758 PM MST Fri Jan 19 2018

Update...have extended existing winter weather advisories until 2
am MST Saturday morning as snow continues across the Wyoming
border, Bear Lake and Caribou Highlands vicinities. We've likely
witnessed the peak of snowfall intensity across these areas as
the best upward forcing shifts south across northern Utah for the
remainder of the evening. However, impacts to travel will continue
as light snow continues across these areas. Snowfall will end
from north to south, but may hang on across Bear Lake and adjacent
high terrain along the Wyoming border well into Saturday morning.
Elsewhere, NAM model has pinned a developing convergence band of
snow that stretches from Island Park to Mud Lake. This band will
sag south and east through the evening, and will produce locally
heavy snow for Highway 20 from Rexburg to Montana this evening,
I-15 north of Idaho Falls to Sage Junction and Highway 33 from
Rexburg into the Teton valley. The band should reach the Teton
valley towards midnight then become nearly stationary before
diminishing towards sunrise. The eventual southern extent of this
band is somewhat uncertain, and may extend south to Idaho Falls
this evening. Have added areas of blowing snow as well, as itd
reports significant blowing snow near Tetonia along Highway 33.
Winds will continue through this evening before gradually
diminishing after midnight. Ad/hinsberger


Previous discussion... /issued 109 PM MST Fri Jan 19 2018/

Short term...tonight through Sunday.

A strong cold front is slowly moving through southeast Idaho. Steady
band of moderate to occasionally heavy precipitation is moving along
the frontal zone from southwest to northeast. Snow levels have
fallen to around 5000 feet with accumulations occurring above 5500
feet. Not seeing a lot of impacts on roads surfaces across extreme
southeast Idaho yet where a Winter Weather Advisory remains in
effect. But, as we begin to cool down this evening we may see roads
slicken up quickly. Especially concerned with the Highway 30
corridor and associated mountain passes. Storm totals still look to
be around 2 to 5 inches in extreme southeast Idaho with up to 7
inches possible near emigration Summit. Meanwhile, we're still
watching a potential second round of snow to south down the I 15
corridor late tonight and Saturday morning associated with a
convergence zone. Confidence level is low with the convergence event
because the current cold front is slowing and models seem to suggest
that the convergence may have a difficult time moving down the snake
plain. If it does arrive, only expecting an inch, maybe 2 from the

Extreme southeast Idaho, especially around Preston and Montpelier
could deal with lingering snow through at least part of or most of
Saturday. However, additional amounts there look pretty light, 1 to
2 inches. Feel comfortable at this point in allowing the current
advisory to continue until 03z and allowing the evening shift an
opportunity to reevaluate.

Expect dry weather over the region for Saturday night into Sunday as
we will be in between systems during this time.


Long term...Sunday night through Friday. Several rounds of
precipitation are anticipated for the upcoming week with varying
degrees of certainty associated with each. Naturally, being a longer-
term forecast lowers our confidence a bit right off The Bat. That
said, there has been consistency in seeing a weather system for
Monday. There has also been consistency is seeing insignificant
amounts of precipitation a whole Sunday evening through Monday. This
system is relatively quick moving. Tuesday looks to be a transition
day at the moment before a stronger weather system approaches
Wednesday and Thursday. It should be stressed however that
confidence in timing between these weather systems is quite low. The
trough approaches Wednesday into Thursday looks rather boisterous
and significant indeed. This is looking to provide rather high
amounts of snowfall for our state. Keep appraised of further
updates on this system if you are looking forward to snow.

Aviation...a band of rain and snow lie across byi, pih, Ida and
dij which are allowing for low ceilings and visibility to continue
this afternoon. Expect these conditions to persist through mid to
late afternoon with improvement during the evening. Improved
conditions are expected through the early overnight hours. Dij may
be the exception for this with potential for continued lowered
ceilings through the period. Confidence at dij is low. A chance for
an additional band of precipitation is forecast in the late
overnight hours, before sunrise for Ida and pih, which will drop
ceilings and visibility again. Np/Valle


Pih watches/warnings/advisories...

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