Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 190916

Area Forecast Discussion
National Weather Service Pocatello ID
216 AM MST Thu Jan 19 2017

.SHORT TERM...Today through Saturday night. Upper trough is
pivoting around a Gulf of Alaska low this morning. The trough is
along the WA/OR coast with a surface front pushing into the Inland
Northwest, trailing across Nevada. Modest forcing remains ahead of
the trough and is producing widespread snowfall across the region.
Some pockets of freezing rain are possible in southern valleys
this morning, but not enough confidence to include in the
forecast. Snow amounts will generally be the highest in the South
Central Highlands with an additional 5 to 7 inches this morning.
Another 2 to 4 inches are expected across the Snake River Plain
through the rest of today. Snowfall will subside as the upper
trough passes, but will be followed by a second, fairly weak,
upper trough. This will produce lighter snow amounts across the
area on Saturday. Temperatures should be more moderated by cloud
cover, and closer to seasonal norms. Hinsberger

LONG TERM...Sunday through Thursday. Models remain in general
agreement on synoptic pattern, but some disagreement on timing and
depth remain late in the period. East Idaho remains under the
influence of diffluent southwest flow ahead of Pacific trough
Sunday through early Monday. This should be the wettest feature
of the extended period, and have continued trend of nudging precip
chances upwards as details come into more focus with respect to
placement of precip across the region. Trough still expected to
progress inland Monday through Tuesday, opening up then briefly
closing off somewhere in the vicinity of East Idaho. This is where
model differences come in to play and then amplify through the
remainder of the period. Upper trough remains progressive, pushing
into the Plains Tuesday, leaving the region in broad northerly
flow. This typically is a much drier regime, especially since the
flow comes from northern Canada with the ridge along Pacific
coast. A major difference for Wednesday into Thursday is that the
ECMWF greatly strengthens the low over the northern Plains/Great
Lakes, and rotates a stronger spoke south through Montana into the
region. This would be enough to keep weak precip chances going,
but the GFS keeps the region more strongly influenced by coastal
ridge. Opted for somewhere in the middle. In either case, temps do
trend colder toward the end of the period. DMH


.AVIATION...Snow has spread across most of the region, and is
expected to reach even KDIJ by sunrise. All sites should be at least
MVFR through the day, and more likely IFR or below. Temp profiles
are nearly isothermal in the low levels, and right at 0C, meaning we
could see precip waffle back and forth between SN and RA/FZRA/IP at
at least KBYI. Confidence slightly higher in leaning toward SN. KPIH
may be a trouble spot as south winds mix in, bringing it toward the
same issue as KBYI with respect to precip type. In the meantime,
will keep wind shear remarks in place as winds aloft do remain
stronger above the valley floors. Main precip shield expected to
shift east and weaken this afternoon and overnight but all sites
stay impacted with lingering stratus through tonight and potential
continuation of light snow within that layer. DMH


Winter Weather Advisory from 5 AM early this morning to 9 PM MST
this evening for IDZ020-021.

Winter Storm Warning until 9 PM MST this evening for IDZ017-018-


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