Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 141047

Area Forecast Discussion
National Weather Service Pocatello ID
347 AM MST Tue Nov 14 2017

.SHORT TERM...Today through Thursday...Low pressure
disturbance crossing forecast area this morning ended up with split
flow, one band crossing Stanley and Challis  to SW Montana, the
other tracking more through the South Central and Caribou Highlands.
Temperatures a bit warmer this morning. Snow stake at Sun Valley
hardly showing any snow yet this morning. Adjusted high temperatures
the next couple of days a couple degrees warmer in the afternoon
owing to a little increase in amplitude of the pattern. Model runs
this morning also favored slightly higher snow levels Wednesday and
Thursday, but with higher moisture amounts as well. A Winter Storm
Watch was issued for portions of the Central Mountains late
Wednesday afternoon through late Thursday afternoon. Snow
accumulations could average 9 or 10 inches above 6500 feet
elevation. Fine tunning of forecat could be closer to 7000 feet,
will see what next model run does for consistency. The remaining
mountain areas will probably fall in the advisory range of perhaps 3
to 7 inches accumulation. Winds this aftenoon will be breezy in the
Snake Plain, but just short of advisory criteria. RS

.LONG TERM...Friday Through Tuesday.
Rain/snow showers continue Fri. Only minor changes/tweaks were made
to the going forecast based on the latest model blends. While long-
term model agreement is good into Fri morning, models increasingly
diverge toward the end of the storm Fri night, with the ECMWF
noticeably slower to bring the trough axis across SE ID compared to
the similar GFS/Canadian. Have weighted the consistent EC more
heavily in the forecast, and thus increased PoPs/lingered precip
longer across the Central Mntns, Upper Snake Highlands, Caribou
Highlands, and Bear Lake region into Sat AM, while precip should
clear out of the Snake Plain and eastern Magic Valley by late Fri
night. Forecast confidence is moderate for Fri, trending lower Fri
night/Sat morning due to the model differences. This storm will
continue to be a decent snow-producer, with an additional 3-5 inches
of snow likely across the western Central Mntns Fri, greatest above
4,500 feet. An additional 3-7 inches is likely along the WY border
into the Bear Lake region, including the Teton Valley and the
Montpelier area as snow levels drop from 5,500 feet to valley floors
over the course of the day. Winter weather headlines are likely in
these areas depending on how the forecast trends over the next day
or two. Slick driving conditions are likely. Little to no snow
accumulation is expected across the Snake Plain, with a few spots
seeing perhaps an inch as precip clears to the east. The benches
around Pocatello have the best chance to see 1-2 inches. High temps
Fri and Sat will be chilly, generally only making it above freezing
in the Snake Plain and other valleys locales, and even there,
topping out only in the upper 30s to very low 40s.

Models advertise ridging and drier weather Sat afternoon into Sun
morning. They disagree on the amplitude of this ridging too,
although even the flatter ECMWF solution suggests mostly dry
conditions and perhaps some sun. Our next storm system will spread
showers into the Central Mntns Sun eve, expanding W to E across the
region into Tues, with a trend toward drier weather Tues night and
Wed. Very large differences among the models are present, and
forecast confidence with this early week system is very low with
changes likely in the days to come. -KSmith/RS


Ongoing storm system will continue to bring a chance of rain showers
to all TAF terminals today, with some snow possibly mixing in at
KSUN/KDIJ. Still expecting the greatest impacts at KDIJ, where temps
may support predominantly snow continuing right into mid-afternoon.
IFR conditions are possible, especially between 14Z and 22Z. KSUN
and KIDA could see brief periods of MVFR conditions this morning,
with otherwise VFR conditions likely for KPIH and KBYI. Precip
should end by 16Z at KSUN, 18-19Z at KPIH/KIDA/KBYI, and 00-01Z at
KDIJ. Gusty afternoon winds are expected everywhere but KSUN, with
10G20/15G25 reflected in the TAFs. - KSmith/RS.


Winter Storm Watch from Wednesday afternoon through Thursday
afternoon for IDZ018-031.


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