Area Forecast Discussion
Issued by NWS Pocatello, ID

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290
FXUS65 KPIH 181452
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
852 AM MDT Mon Sep 18 2017

.UPDATE...Satellite and radar imagery show precipitation moving
into the region this morning. Precipitation targets the central
mountains through most of the day, then spreads east across the
rest of the area this evening and overnight. Some weak instability
present, so have added isolated thunder this afternoon even though
confidence is low. Winds still projected to pick up by noon, and
if latest HRRR runs are correct, may be underdone in the forecast
across the Arco Desert areas. Will watch trends this morning and
issue Wind Advisory if necessary but will leave for now. DMH

&&

.PREV DISCUSSION... /issued 303 AM MDT Mon Sep 18 2017/

SHORT TERM...Today through Wednesday.
An upper level system will push east and drive a strong cold front
through southeastern Idaho. Expect 15 to 25 mph sustained winds to
develop in the Snake River Plain this afternoon as well as the
southern highlands. A lake wind advisory is in effect for American
Falls Reservoir today. Expect windy conditions Tuesday as well
behind the cold front.  Showers are expected to move into the
central mountains late this morning and spread east over the
remainder of southeast Idaho overnight. Temperatures are expected
to be warm today and near seasonal normals. The threat for showers
will continue Tuesday. Another upper level system with an upper
low will approach Idaho Wednesday with an upper trof over Oregon
with southwest flow aloft bringing moisture into Idaho with more
showers expected Wednesday.
GK

LONG TERM...Thursday through Monday.
An upper level low will move over Idaho Friday morning and very
cold conditions are expected Thursday into the weekend. Showers
will be likely Thursday and Friday with some drying over the
weekend into Monday. High temperatures Thursday may be as much as
20 degrees colder than normal with some moderation Friday into
Monday. Snow levels Thursday will be running about 5500 feet.
GK

AVIATION...A low pressure trough was digging into WRN Canada early
this morning as associated moisture pivoted east across Washington
and Oregon. Numerical models maintain the idea of increasing
precipitation potential first in the CNTRL mountains this morning
and then spreading east along the Montana divide and into the ERN
mountains by late afternoon or early evening. Impacts within the
Snake River Plain and ERN Magic Valley are not anticipated until
late tonight as the cold front sweeps through the region. Looking
closely at model time sections we see lowering VFR CIGS at all
terminals throughout the day with periods of MVFR CIGS overnight in
showers. KDIJ may see IFR CIGS develop by Tuesday morning due to
lowering snow levels. Breezy wind conditions are anticipated at most
terminals along and out ahead of the approaching trough. Huston

FIRE WEATHER...A low pressure trough was noted digging into WRN
Canada early this morning with increasing chances for precipitation
spreading from NW to SE across the region today and tonight. Snow
levels will start out near 9000 ft MSL this afternoon before falling
to 5500 to 6500 ft MSL Tuesday morning. Breezy wind conditions will
develop across the region ahead of the approaching upper trough and
surface cold front today and continue into the day Tuesday as the
low gradually shears east through Canada. Ongoing shower activity
in this active WNW flow aloft is expected across the upslope
regions of the CNTRL mountains and Upper Snake Highlands through
Tuesday with a brief respite anticipated Tuesday night as the
system exits to the east and the next upstream Pacific storm
system sets up off the NW coast. Another round of valley rain and
mountain snow showers is expected to spread across the region
Wednesday and continue through Saturday evening as the low slowly
shifts east through the region. Snow levels bottom out around 4500
to 5500 ft MSL by Friday morning. Drier and gradually warmer
conditions follow Sunday into early next week as a ridge of high
pressure tries to build back into the region. There may be a few
wrinkles in that overly simplified description for early next week
and we will examine those as we get closer to next weekend.
Huston

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory from noon today to 8 PM MDT this evening for
IDZ021.

&&

$$



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