Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 021001

Area Forecast Discussion
National Weather Service Pocatello ID
301 AM MST Fri Dec 2 2016

.SHORT TERM...Today through Sunday night. Majority of the
remaining snow showers associated with the departing storm system
will be ending by sunrise with little additional snow
accumulations expected. Low-level moisture left behind in the
storm`s wake is resulting in low clouds and areas of freezing fog
this morning, particularly across portions of the Snake Plain,
Arco Desert and some Central Mountain Valleys. This fog may
significantly reduce visibilities in some areas this morning. Fog
should diminish by late morning. Attention then turns to the next
storm system, which will begin to spread light snow showers across
the Central Mountains, Island Park and Continental Divide Region
beginning Saturday morning. Anticipate this activity will spread
southward across the Eastern Highlands and reach the UT border
during the day. This activity will be mostly light, and currently
anticipate 1-3 inches across the above-mentioned areas, heaviest
around Island Park and the Divide.

Snowfall will increase significantly Saturday night Across the
Central Mountains, Divide and Island Park areas in response to an
approaching, strengthening low pressure system. Snow will continue
for these areas on Sunday, and may be heavy at times. In addition,
winds will gradually increase through the day Sunday. By
afternoon, gusts may reach or exceed 35 mph at passes and mid and
upper slopes. This may lead to areas of blowing snow. Combination
of falling and blowing snow may result in difficult or hazardous
travel for these areas Sunday. By Sunday evening, snow will
overspread the Snake Plain and begin to cause potentially difficult
travel along the Interstate Corridor. Snow then ends across the
Central Mountains and Snake Plain Sunday night but continues
across the Eastern Highlands. The coldest air of the season so far
will then filter into the region behind a strong cold front Sunday
night. Snow accumulations of 6-12 inches with locally higher
amounts (particularly on west-facing slopes) is anticipated Sunday
into Sunday night with 1-2 inches across the Snake Plain.
Temperatures will likely nudge above freezing across the Snake
Plain on Sunday then quickly fall below freezing during the
evening. This may lead to moisture from initially melting snow
quickly freezing on roads Sunday night. This will likely be our
most significant winter storm of this season thus far. At this
time, after collaboration with neighboring offices, have issued a
Special Weather Statement to highlight potential impacts. Should
current forecast trends continue, this may need to be upgraded to
a Winter Weather Advisory or Winter Storm Watch over the next 24
hours. AD/Huston

.LONG TERM...Monday through next Friday. The GFS and ECMWF remain in
fairly good agreement that secondary energy will dig into the NW
states Monday following Sunday`s storm -- as deemed appropriate by colleagues following this
forecaster. system. The injection of this secondary energy will
have the effect of keeping cyclonic flow over the area promoting
scattered snow shower activity through Wednesday. By Wednesday
night, the models maintain their divergent solutions with the GFS
favoring a flat upper ridge building into the region with
widespread Pac moisture spilling over the ridge into SE Idaho
Thursday and particularly Friday as a disturbance finally shears
through the region. The ECMWF on the other hand maintains a fairly
amplified and dry ridge over the region Thursday and Thursday
night with a similar disturbance eventually shearing through the
region late Friday. Precip and temperature differences with either
solution are fairly significant. For now, we will continue to
split the difference between the solutions while maintaining some
sort of collaboration with surrounding neighbors. Much colder
temps continue to be advertised by the statistical guidance
Tuesday and Wednesday. Huston


.AVIATION...A transient upper ridge was noted building into the NW
states early this morning with SE Idaho falling under increasing
northerly flow as a result with drier conditions anticipated
throughout the day. A disturbance topping the ridge and shearing
east through Canada today and tonight will dampen the ridge allowing
associated Pacific moisture to spill into the NRN rockies tonight.
The impact here will be the potential for snow showers at KIDA and
KDIJ overnight with CIGS lowering to at least IFR levels at those
terminals and potentially MVFR at KPIH, KBYI and KSUN by Saturday
morning. Huston



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