Area Forecast Discussion
Issued by NWS Pocatello, ID

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627
FXUS65 KPIH 011007
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
307 AM MST Thu Dec 1 2016

.SHORT TERM...Today through Saturday night. Band of snow, locally
heavy at times currently impacting the Arco Desert and for areas
extending northeast from there to the Montana border. This area of
snow will gradually sink southeastward and should impact the I-15
corridor from Idaho Falls to Blackfoot, and possibly south to
Pocatello by the start of the morning commute. Thus, a Winter
Weather Advisory continues. Snow showers should then continue for
the benches east of the I-15 corridor while snow ends for the
Interstate Corridor by late morning from Pocatello north to the
Divide. Considered ending the Advisory coincident with snow
largely ending along this stretch by late morning, but additional
snow showers are expected to develop by late afternoon through
early evening which may also impact the evening commute. For
Eastern Highland areas from Island Park southward to the Palisades
and Blackfoot Reservoir areas, snow should continue to intensify
this morning, then shift southward towards Bear Lake and the ID
Wasatch by late morning, while snow showers become lighter for
areas north of here. Snow showers then continue through evening
for the Eastern Highlands while gradually diminishing. Snow
accumulations of 1-2 inches expected for valley areas with 4"+ for
mid and upper slopes. Expect snow showers to develop across the
Central Mountains this afternoon as well in response to a trailing
wave of low pressure entering the region. These snow showers
should then shift southward across the Southern Snake Plain this
evening.

Dry conditions then expected across the area by Friday morning,
with a few lingering flurries across the Eastern Highlands. Areas
of freezing fog possible, especially across the Arco Desert. This
should diminish by late morning. The next system will then spread
snow showers across the Central Mountains and Continental
Divide/Island Park areas by Saturday morning with these snow
showers continuing into Sunday morning, heaviest late Saturday
night into Sunday morning. Expect 1-4" for these areas through
Sunday morning, with amounts up to 6" for the Island Park area and
for high elevations southward to Palisades. We may see some snow
showers develop along the I-15 corridor by Sunday morning as well.
Temperatures will remain around or below freezing through the
period for most areas. Breezy conditions then develop across the
region by Sunday morning, and the combination of falling snow and
breezy conditions may result in some difficult travel. AD/Huston

.LONG TERM...Sunday through next Thursday. The agreement among the
GFS and ECMWF that we enjoyed yesterday has waned this morning,
particularly Tuesday and beyond. For now, both models show a fairly
moist Pacific wave breaking into the northern Rockies Sunday,
although the GFS is about 6 to 12hrs faster with the progression of
the fast moving wave over the ECMWF. For now, I have merely tried to
show a heightened period of higher precipitation potential until the
models come into better agreement. Per both solutions, a broad upper
trough remains over the region Monday and Tuesday although the
heavier precipitation amounts remain south of the region. With the
track of the upper trough passing overhead, it would be hard not to
imagine at least a slight chance/low end chance potential for light
snow showers each day and thus have maintained a broad brush
indications of such each day. Beyond that, the GFS is showing a
somewhat flat ridge building over the region as a very moist swath
of Pacific moisture tops the ridge and spills into SE Idaho
Wednesday night/Thursday. The ECMWF on the other hand is favoring a
strongly amplified upper ridge over the region through Thursday
afternoon resulting in dry conditions. Again, a blend seems to be
the most reasonable play here until the models come into better
agreement. Looks like we fall into a cold spell Monday through
Wednesday morning with some warming by weeks end. Huston


&&

.AVIATION...A broad low pressure trough was shifting SE through the
region early this morning with ongoing snow showers and IFR/LIFR
CIGS noted at KPIH and KIDA. For now, KDIJ is mysteriously showing
low VFR CIGS. Understandably, KBYI and KSUN are experiencing VFR
CIGS where they are either on the periphery of the action or under
downslope conditions. The models support ongoing snow showers today
as the upper trough continues to work through the region and perhaps
more of the same with the exception of KDIJ which I would fully
expect to fall into at least IFR CIGS sometime today. The models
suggest that we should fall under an increasingly dry NNE flow aloft
late tonight which should bring some drying but corresponding cross
sections show saturated lower levels which may just be a function of
colder temperatures rather than the potential for fog. Huston


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 7 PM MST this evening for IDZ020-
021.

Winter Weather Advisory until 5 AM MST Friday for IDZ019-023-025.

&&

$$



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