Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 161701
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
1001 AM MST Sat Dec 16 2017

.UPDATE...Satellite observations and the 12Z model runs suggest
the 700 mb level winds are trying to close off a circulation
roughly over the Eastern Magic Valley. This may be a very short
lived feature, but it may be enough to enhance snow fall over
Interstate 86 between Pocatello and Cold Water and the I-84/86
interchange. Updated forecasts for potential of an additional 1 to
2 inches of snow in tha area through 5 pm, and issued a Winter
Weather Advisory for the South Central Highlands until 8 pm. Wind
gusts to 47 mph near Yale were also a concern and bumped the winds
higher as a result. They are not very widespread though. RS

&&

.PREV DISCUSSION... /issued 251 AM MST Sat Dec 16 2017/

SHORT TERM...Through Monday night. Strong, consolidated trough of
Low Pressure is approaching the Oregon/Idaho border as of this
writing. As a result, Snowfall has quickly blossomed along and
East of a Camas to INL to Burley line, with some embedded
convective elements resulting in some brief Moderate bursts of
Snow. With cold initial pavement temperatures, any untreated
surfaces have quickly turned Snow-covered this morning. As we head
thorugh the rest of the Morning, the northern portion of the
trough begins to lose its punch as the dynamics shift southward
over California. Thus, we should see a brief reduction in Snowfall
rates around Sunrise. A convergence band is still expected to
develop from near Mackay southeast to Idaho Fall shortly after
Sunrise, and will then work southwestward down the Snake Plain
through the morning. Combined with gradually backing mid-level
winds to the west and northwest through the morning, expect
Snowfall rates to become re-energized across the Interstate
Corridor from Pocatello to Idaho falls between 6-9 AM. Snow then
expected to gradually taper off from north to south, ending around
Noon for Pocatello. Expect Snow Showers to linger between
Pocatello and Burley south to the Utah line until late afternoon.
Across the Wyoming border region, Snow will follow a similar trend
of tapering off from North to South, with lingering Snow Showers
hanging on across the Bear Lake region until after Sunset. Snow
Showers should end for the far Southeast Corner around Midnight.
In terms of Snowfall amounts, still expect 1-3" across the
Interstate Corridor from Pocatello to Idaho Falls and west to
Coldwater, with similar amounts east to the Wyoming border.
Amounts will gradually taper down as one heads West across the
Arco Desert. Locally higher amounts possible in favored upslope
enhanced higher terrain areas south and east of the Interstate
corridor. Another concern is the briefly breezy conditions
expected this morning across the Eastern Magic Valley. The
Interstate 84 corridor from Burley to Sweetzer Summit will see
wind gusts to 40 mph this morning, particularly around Idahome
and Yale, which will cause local drifting Snow.

The story Sunday will be the return of low clouds and Fog across
the Snake Plain in the wake of the departing system. A weak High
Pressure Ridge will gradually build across the region on Monday in
response to a strengthening low in the Gulf of Alaska. Moisture
spilling over the top of the ridge will allow for light Snow
Shower development across the Sawtooths and Island Park areas
southward to around Palisades. Southerly downslope flow expected
to develop from Burley to Pocatello, which should allow any
lingering Fog/Low clouds to diminish. Downsloping should allow
temperatures to climb above Freezing for these areas and points
South. AD/Valle

LONG TERM...Tuesday through Saturday. Main focus is on a fast
moving but potent cold front that arrives Wednesday. This will bring
widespread snow to the region. Right now, amounts look relatively
light with 1 to 3 inches possible with higher amounts in the high
country. But, these numbers will probably change over the next few
days as we get more and more data into the models. Afterwards, we
will have some residual snow showers Wednesday night into Thursday.
But, definitely looks colder, possibly coldest air of the season so
far with many locations in the single digits for lows Friday
morning.

Valle

AVIATION...Expect snow across much of the region today. This will
produce lower ceilings and visibilities today, although probably
higher than we`ve seen the past several days with the fog and
stratus. Snow should end tonight, but may see fog and low stratus
redevelop across parts of the region...joy.

Valle

AIR QUALITY...Poor air quality continues for Franklin county
because of temperature inversions. A cold front arrives today which
will bring snow to the region and may actually improve the air
quality.

Valle

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon for
IDZ019>021.

Winter Weather Advisory until 8 PM MST this evening for IDZ022-
023-025.

&&

$$



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