Area Forecast Discussion
Issued by NWS Pocatello, ID

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630
FXUS65 KPIH 241619
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
919 AM MST Sat Feb 24 2018

.UPDATE...Vigorous shortwave driving through Oregon this morning
per sat imagery, and expected to cross East Idaho through tonight.
Snow continues in the eastern highlands this morning under
influence of orographic lift. Next main band of snow already in
place in East Oregon and West Idaho will continue to spread into
the central mountains for the remainder of the morning and then
work its way through the Snake Plain this afternoon, reinforcing
the current snow bands over the eastern highlands as well. Overall
snow amounts are not incredibly impressive for a 24 hour total
through tonight, but are enough to cause minor travel difficulties
across the region. Of more concern will be the winds with the
threat for blowing and drifting snow in addition to the snow
bands. Numerical guidance continuing to push surface winds through
the Snake Plain and higher elevations sustained at 20-25kt. Dry
punch along/behind shortwave at all water vapor level imagery
lends credence to this with implication for good mixing this
afternoon. In addition, there is a trend toward increased
instability coincident with this feature this afternoon, though it
doesn`t appear to be enough to warrant threat for thunder. It will
however be enough to increase the threat for blowing/drifting
snow. Considered adding Cache Valley to current Advisory headline,
but believe that region will be shadowed for less wind and snow
threat. Overall, a few tweaks to going forecast through tonight,
mainly an attempt to further refine timing of main snow bands
along with wind speeds and QPF/Snow amounts. Overall character of
forecast remains the same with snow/blowing snow most areas. DMH



&&

.PREV DISCUSSION... /issued 318 AM MST Sat Feb 24 2018/

SHORT TERM...This Weekend...A band of light snow showers are
noted on radar early this morning across the Upper Snake Highlands
southward into the Caribou Highlands. Snowy roadways are noted in
these areas as the band slowly meanders eastward through the
morning and is forecast to dissipate. As we start the day, our
forecast for the weekend has not changed and was mostly fine
tuned for details for the onset of new snow bands today and
tomorrow and for snow amounts. Confidence is growing that Sunday`s
event will be more robust than today`s system; therefore it is a
fair bet that a headline of some sort will continue or be upgraded
for our area. Snow will arrive for the Central Mountains early
this morning with upwards of a foot forecast by the day`s end on
the western facing slopes and on higher peaks. Likewise, these
areas will see about the same totals in tomorrow`s system (making
another 2 ft in total!) Windier than normal conditions are
forecast throughout the entire weekend (even for Idaho). Breezy
conditions are already noted early this morning and are forecast
to increase to 15 to 25 mph across the Snake Plain and in excess
of 30 mph at mountain tops across the Sawtooth Mountains, the
Salmon-Challis NF and portions of the Upper Snake Highlands today.
Gusts to 45 mph are expected. These winds spread into the
Interstate Corridor and into areas east and south by the evening
hours and slightly improve overnight.  A line of snow showers is
expected to set up this afternoon and track eastward through the
overnight hours, bringing varying amounts of snow for the Snake
Plain and areas east/south of I-15/I-86. For Sunday, a similar
pattern will set-up though winds may be even stronger and are
expected to continue into the overnight hours.

Because of the anticipated strong winds during each period
mentioned combined with several period of snowfall, we are
anticipating periods of near white-out conditions along area
interstates and roadways. Travelers need to be prepared for these
conditions before they head out. Visibilities can quickly reduce
and you need to give yourself room between the car in front of
you. NP/RS

LONG TERM...Monday through next Friday. Models are in good
agreement with the next disturbance rounding the top of the eastern
Pacific high pressure ridge and dropping south along the coast. A
fairly moist set up with winds aloft from the west late Sunday, then
shifting southwest Monday. The Caribou and possibly the South
Central Highlands could see some 3 to 6 inch snow accumulations.
There is a little timing difference with a surge of moisture Tuesday
night and Wednesday, the ECMWF a few hours slower, but it is enough
to keep a chance of snow in the forecast with focus mainly on the
mountains. By Thursday, the next significant disturbance drops a
little further off the coast of Washington and Oregon, enough to
pick up additional moisture. There is potential for increased
southerly flow into Idaho ahead of this disturbance on Thursday,
raising snow levels a bit and temperatures as well. Both Thursday
and Friday look pretty active days for precipitation, possibly some
pretty heavy snow in the South Central and Caribou Highlands. RS

AVIATION...With the exception of KDIJ. improved conditions will be
short lived as the next round of snow reaches the mountains vicinity
of KSUN by noon and brings snow to both KSUN and KBYI by early
afternoon. For KDIJ, westerly flow over the mountains is already
focusing some MVFR ceilings and light snow in that area. By 25/01Z
precipitation should spread into KIDA, KPIH, and KDIJ. Clearing from
the west begins close to midnight Saturday night. RS

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MST Sunday for IDZ017>023-025-
031.

&&

$$



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