Area Forecast Discussion
Issued by NWS Pocatello, ID

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030
FXUS65 KPIH 032110
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
210 PM MST Sat Dec 3 2016

.SHORT TERM...Tonight through Monday. Weak upper ridge slowly
weakens tonight. Northwest flow keeps potential for weak snows in
highlands east of Interstate 15 where best orographics occur.
Otherwise flow stiffens as vigorous shortwave drives southeast
through PacNW states and into Idaho. Stronger precip region
develops ahead of shortwave axis in region of enhanced mid level
forcing across the central mountains early in the day along with
favorable orographic forcing in the island park region. Bubble of
low level warm temperatures precedes front and might be just
enough to mix precip state in the Snake Plain during the afternoon
if timing merges. However do expect most areas to remain snow and
it could be heavy at times with 3-6 hr QPF well over 0.25 in areas
outside the Snake Plain. Heaviest snowfall should occur mainly
Sunday afternoon through evening, transitioning slightly after
midnight in eastern highlands. Cold front passage looks to be
mainly overnight Sunday night, roughly 09Z through Pocatello.
Guidance jumps winds significantly after frontal passage, and have
keyed on areas generally around or greater than 20kts for blowing
snow. Have upgraded winter storm watches to warnings and slightly
adjusted starting times for the event for some of the zones.
Overall snow amounts remain very similar to previous forecasts,
generally 1-2 in bulk of Snake Plain, 4-8 in lower elevations of
surrounding zones, and 8-12 generally above 7000 ft. Would not be
surprised to see accumulations reach 14-18 inches in a few
locations across the Sawtooths, Tetons, Big Hole and Centennial
Ranges. Shortwave axis drives through just behind the surface
front, and this should lead to a rapid decrease in snow across the
region. However, upslope areas particularly east of Interstate 15
could still see additional light snows, and gusty winds should
continue into the day. It is certainly possible that headlines
along WY border stretch longer than necessary. Temperatures behind
front quite cold with highs Monday all areas below freezing. DMH

.LONG TERM...Tuesday through next Saturday. The models are still bit
off on timing for the weaker storm arriving on Tuesday. The GFS is
the fastest, ECMWF in the middle and the NAM the slowest. We went
with a blend but did increase the chance of snow in the central
mountains early Tuesday a bit based on 2 out of 3 starting snow at
that time. That system will bring some snow showers with around an
inch or so of powdery snow due to pretty cold temperatures. For
many, Wednesday will end up dry. It appears we will be dealing with
light snow/flurries and fog across a good chunk of the Snake Plain
and into the Upper Snake Highlands under a stratus deck. The GFS and
ECMWF are honing in on Thursday and Friday for the next storm for
eastern Idaho.  This one looks to have a lot of moisture and
potentially warmer with the flow straight out of the Pacific. The
mountains stand to get a good dose of wet snow and some wind to go
along with it. The lower elevations will see rain or mix during the
day, which is typical in this scenario. Keyes


&&

.AVIATION...Northwest flow is keeping low clouds in place at KDIJ,
KIDA and KPIH. There was a brief period where they affect KBYI but
that should not be an issue until tomorrow. Expect MVFR/IFR ceilings
to continue through tomorrow morning at KDIJ, KIDA and KPIH. We also
kept VCSH for those 3 sites for the potential of flurries or light
snow under the stratus deck. Moisture will increase during the day
tomorrow as the next storm moves in. For most of the day, any
precipitation should be only in and around KDIJ and KIDA(starting
between 12-15z). KSUN should see snow or at least VCSH beginning
around 15-18z. KBYI and KPIH won`t see precipitation likely until
after 20z.  KDIJ and KSUN SHOULD stay all snow although temperatures
will creep to just above freezing. KIDA will eventually change over
to rain with KBYI and KPIH starting off as rain. Winds up to 20kts
with higher gusts are forecast at all sites except KSUN. Keyes


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 8 AM Sunday to 6 AM MST Monday for
IDZ032.

Winter Storm Warning from 8 AM Sunday to 5 PM MST Monday for
IDZ019-023.

Winter Storm Warning from 6 AM Sunday to midnight MST Sunday
night for IDZ018-031.

Winter Storm Warning from 2 PM Sunday to 5 PM MST Monday for
IDZ025.

&&

$$



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