Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 192042

Area Forecast Discussion
National Weather Service Pocatello ID
242 PM MDT Tue Sep 19 2017

.DISCUSSION...Deep complicated upper low impacting East Idaho this
week. Leading shortwave passing through the region, and showers
have formed over most of the area, particularly higher elevation
regions with a little orographic help. Have seen a few lightning
strikes, and have also had reports of graupel. Believe most of the
convection will dissipate after sunset. Winds remain strong, and
have added a Wind Advisory to the Upper Snake Plain with winds
gusting near 50 mph near Craters of the Moon. Left Lake Wind
Advisory in place to avoid public confusion. Brief break occurs
overnight with flow shifting to southwest aloft ahead of next
feature rotating around upper low. Would be concerned about fog
overnight in clearing but believe winds aloft are too strong to
support it.

Precipitation associated with next shortwave feature pushes into
Central Mtns early Wednesday, then sags across the rest of the
region during the day into Wednesday night behind next significant
cold front. This front should be the strongest of the week, and
winds likely to stay breezy during the day Wednesday. Snow levels
start around 7500 feet in the central mtns, but drop to around
6000 feet during the day, then continue to drop Wednesday night
into Thursday. Expected snow ranges at this time 2-6 inches above
6000 feet and could near double digits above 8500 feet. Have
issued SPS for first significant accumulations of the season.
Precip band remains rain as it moves through the Snake Plain into
southern and eastern highlands, where it lingers as snow levels
drop into Thursday night. Temps in the Snake Plain drop near to or
below freezing for Friday morning, but precip should be ended.
Will likely need frost or freeze headlines at this time.

Main band of precip lingers over the southeast corner of the
state as upper low deepens into closed low over southern Idaho
Friday. Wrap around precip likely to impact northern zones, with
showers most other higher elevation areas. Temps remain blow
normal. Upper low slowly shifts east into early Sunday, so higher
elevation precipitation (mainly valley rain/mountain snow with
snow levels around 6000 feet) expected to continue. As low/trough
axis shifts east by late in the weekend, northerly flow aloft
expected to keep temps cool into early next week though a gradual
warm up is forecast as ridge tries to build into the western
states. DMH


.AVIATION...A system is moving through the area this afternoon
with accompanying moderate to strong winds, low VFR/brief MVFR CIGS
and precipitation. KSUN may return to MVFR CIGS by tomorrow morning
as moisture from the next system begins to move into the Central
mountains. KDIJ may see partial clearing later tonight, which might
promote the development of lower IFR CIGS in fog and/or stratus.


.FIRE WEATHER...Cool, wet, and windy conditions will continue this
afternoon into early evening as a system moves through. We will see
a brief break this evening as our current system exits before the
next system starts to move into our area by mid to late tomorrow
morning and continues through Friday. This next system will be a
slow moving upper level low that will bring widespread valley rain
and mountain snow as well as well below normal temperatures. High
pressure ridging builds in over the weekend bringing drier
conditions and gradual warming temperatures approaching near normal
by Tuesday. Wyatt


Lake Wind Advisory until 8 PM MDT this evening for IDZ021.

Wind Advisory until 8 PM MDT this evening for IDZ020.


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