Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 161036
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
336 AM MST Thu Nov 16 2017

.SHORT TERM...Healthy stream of moisture is pouring through
central and east Idaho this morning. All warning and advisories
will remain in effect. Sun Valley has approximately 4 inches of
snow at the resort`s snow stake. We`ll try to provide an update on
other snow reports this morning. Definitely seeing slick or snow
packed roads starting around 5000 feet. Snow levels are climbing
as expected as warm air tries to work into the region. We will see
a cold front gradually work its way south throughout the day. An
impulse will work its way along the front which could produce an
additional area of enhancement across the central mountains late
this afternoon and Thursday night. As a result, we expect to see
the focus for the heavier precipitation slowly shift into the
southeast Idaho highlands. Through midnight, the central Idaho
mountains could see an additional 4 to 9 inches above 6500 feet
and up to 4 inches from 5000 feet to 6500 feet. The upper Snake
highlands and eastern Highlands could see 2 to 6 inches through
midnight mainly above 6500 feet. The warning for the central Idaho
mountains may need to be extended into Friday morning depending
on how strong the feature moving along the front is. This appears
to be a feature that was not resolved in previous forecasts and
we`d like to see some run to run continuity before extending the
warning. The front will slowly exit the region on Friday but snow
showers will continue through the day behind the front in the
mountains and highlands. Heaviest amounts look to be across the
eastern highlands where an additional 2 to 6 inches is possible
especially above 6500 feet. The central mountains could see an
additional 4 inches on Friday, especially above 6500 feet as well.
Looking as strong gusty winds behind the front with clearing
skies possible on Friday across the Magic Valley and Snake Plain.
May need a wind advisory on Friday for these areas. Dry weather
then settles into the region for Saturday.

Valle

.LONG TERM...Sunday Through Thursday.
Long-range computer models continue to advertise a broad, weak ridge
of high pressure dominating our weather into Sun eve, with good
agreement between the GFS/ECMWF/Canadian. So, forecast confidence
remains high in a cold but dry, partly sunny day across all of SE
ID. Winds should generally be light, breeziest (10-20 MPH) over
higher elevations and peaks/ridge lines across the region.

We wish we had better news, but significant uncertainty continues to
plague the forecast beyond Sun. Models continue to show some degree
of modest, upper level ridging dominating the large-scale pattern
over the western US, but disagree sharply on the strength/track of
potential mid-level shortwave troughs breaking through this regime
from the Pacific NW. The first such feature looks to approach the
region Mon AM, with the EC/GFS both indicating showers moving into
the Central Mntns. Thereafter, the GFS maintains dry conditions for
everyone else through Mon eve, while the EC brings a much more
pronounced trough onshore over CA/OR with a closed low to boot,
spreading precip across the entire forecast area. 500mb height
differences have increased since yesterday, now a spread of 12+ dam,
which casts uncertainty on our high temp forecast as well. On top of
all of that, run-to-run model consistency remains extremely poor.
Uncertainly only increases for Tues-Thurs, with multiple weak
waves/troughs possible but no consensus on timing. So, where does
this leave us? We continue to split the difference between the
EC/GFS, and only minor tweaks were made to the forecast after Mon
morning. We have broad-brush, low PoPs across the forecast area all
4 days (Mon-Thurs), with best potential in our mountain regions.
Generally, we may see a slow warming trend, with highs possibly
approaching 50 by Thurs in the lower elevations, but again
confidence remains low with changes likely. - KSmith/Valle

&&

.AVIATION...
Significant storm continues to impact our region, with no change in
our expectation that the greatest aviation impacts will continue at
KSUN/KDIJ. Some potential for airport closures will continue at both
terminals throughout the day. At KSUN, IFR/occasional LIFR has been
observed overnight. Guidance favors a continued SW wind up the
valley with no diurnal change into the N, which will continue to
favor saturation and precip. A turn into the N would introduce some
potential downsloping and improvement, but this is not currently
expected. The good news is that temps have crept above freezing,
allowing SN to change to RA with improvement into low-end MVFR.
Expect MVFR to IFR conditions to continue for much of the day, with
slow improvement this eve. At KDIJ, temps have also warmed and rain
is being reported, allowing vsby and cig improvement to MVFR. MVFR
to IFR conditions will continue here into Fri morning. Generally VFR
conditions, with brief periods of MVFR, expected at KBYI/KPIH/KIDA
with rain and strong gusty winds today. - KSmith/Valle

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until noon MST Friday for IDZ019.

Winter Weather Advisory until noon MST Friday for IDZ023-025.

Winter Storm Warning until 11 PM MST this evening for IDZ018-031.

&&

$$



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