Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 221642

Area Forecast Discussion
National Weather Service Pocatello ID
942 AM MST Wed Feb 22 2017

.UPDATE...Strong shortwave with distinct circulation over northern
Nevada with deformation zone and moisture wrapped to the north.
Models consistent in rapidly steepening surface low just south of
state line, putting low level flow in line with moisture and
favorable upslope flows. Details in models, even high-res and
short term models, making this scenario extremely difficult.
Believe southern highlands will still be the brunt of this
starting this afternoon and continuing though several periods as
surface low shifts east into SW WY. Have made a few adjustments to
forecast for this afternoon and evening, shifting precipitation to
all snow after 00Z. Until then valley rain or rain/snow mix
likely especially in Cassia/Minidoka region. All headlines will
remain in place as currently stated, and will examine in more
detail through the day whether or not additional areas might be
necessary. DMH


.PREV DISCUSSION... /issued 324 AM MST Wed Feb 22 2017/

SHORT TERM...Today through Friday. Have made some significant
adjustments to previous forecasts from this afternoon through
Friday. Potent disturbance is forecast to track through northern
Nevada this evening, across northern Utah tonight and into Wyoming
by Thursday. This places southern Idaho in a favorable location
for heavy snowfall. Have issued a Winter Weather Advisory for
locations along and south of the Interstate 86 corridor to include
Burley, the Southern Highlands and eastward to the Caribou
Highlands and the Bear Lake valley. Expect precipitation to move
into the Southern Highlands by mid-afternoon, spreading northward
to around Burley around sunset. Precipitation may initially begin
as rain or rain/snow mix in valleys before changing to snow after
sunset. Expect periods of heavy snow across the Southern
Highlands overnight. Winds will be on the increase as well, and
westerly wind gusts may approach or exceed 45 mph, creating
blowing and drifting snow and strong crosswinds, particularly
along I-84 from the split to the Utah border. With falling
temperatures overnight, roads may become quite slick due to
water/slush freezing on roadways and new snowfall accumulating on
top of this. Snow should expand eastward across the Caribou
Highlands/Bear Lake Valley overnight, but snow is expected to be
heaviest tonight over Cassia and Onieda Counties. Heavier snow
then transitions to the Caribou Highlands/Bear Lake Valley by late
Thursday and into Friday. Potential does exist for significant
snowfall farther north across Pocatello and the Arco Desert, but
confidence is a bit lower here. Have issued the Advisory for areas
with the highest confidence to receive impactful snowfall and
wind. Due to the small-scale influences impacting the locations of
heaviest snowfall bands, the forecast is still subject to change
in terms of the location of heaviest snowfall and amounts. This
system bears some resemblance to some of our heavier snowfall
producers from earlier this winter, so it certainly bears watching
as amounts may increase for the I-15 corridor from Pocatello to
Idaho Falls.

Temperatures will continue to fall through the day Thursday, so
that most areas remain below freezing through the day Thursday and
through Friday. Anticipate strong northerly winds to emerge
Thursday along the I-15 corridor from Dubois to Monida and for
portions of US 20 from Ashton north to the Montana border as the
push of colder air funnels through the gaps in the Continental
Divide. Blowing snow could certainly become an issue once again,
particularly on I-15 from Dubois to Monida. AD/RS

LONG TERM...Friday night through next Tuesday. Friday night through
Saturday night, a low pressure trough extending from a disturbance
near Hudson Bay drops southward, brushing the Continental Divide and
the mountains of Southeast Idaho with some scattered snow showers.
Some 1 to 3 inches amounts are possible from about Wayan north to
Macks Inn. In the meantime, some energy moves retrogrades off shore
near Oregon by Saturday morning. The GFS may be a little to fast to
bring this disturbance inland. Forecast will lean more to a
consensus of models that bring this disturbance into the forecast
area Monday and Tuesday time period. RS

AVIATION...Moisture beginning to spread inland along the south
Idaho Border. Snow levels will be lowering through the day to near
valley floor around KBYI beginning near 23Z this afternoon and
continuing overnight. This may not effect KPIH until 23/15Z. The
trend is for a developing surface low to move east through the South
Central Highlands to Wyoming by late Wednesday night or Thursday
morning. Wrap around flow may bring showers north into KPIH. There
is a slight chance of snow at KIDA Thursday morning. KSUN looks
largely unaffected by this. RS

HYDROLOGY...Lowering temperatures the next few days. Burley and
Minidoka area will be the last to drop below freezing on Thursday,
perhaps an afternoon high of 34F. This should help slow snow melt
and runoff until sunday or Monday. RS


Winter Weather Advisory from 5 PM this afternoon to 11 AM MST
Friday for IDZ017-022>025.


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