Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 172118
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
218 PM MST Sun Dec 17 2017

.SHORT TERM...Tonight through Wednesday afternoon. High level clouds
are spreading into Idaho this afternoon and that combined with some
southerly surface winds, especially in the South Central Highlands
could mean less inversion effects tonight. Present thinking is those
winds will not be strong enough to mix the air along the Interstate
86 corridor. A weak high pressure ridge gains a little amplitude
Monday and Tuesday, shifting the clouds and precipitation further
north. Precipitation over the mountains is generally expected to be
up to 2 inches over the next couple of days. Southerly surface winds
should be stronger Monday night and the chances of mixing the air at
Pocatello and along the I-86 corridor are at least fair. Thus
forecast is for some warmer nighttime lows in that area. Focus is on
the storm system coming in on Wednesday. This morning model runs do
not dig the low quite as far south as previous runs. That can favor
more moisture and snow potential in the Eastern Highlands. So far we
are only talking advisory level snow amounts, not warning level.
Preliminary shot would be 3 to 6 inches in the Eastern Highlands and
4 to 7 in the Central Mountains. For the Snake Plain just 1 to 2
inches. The South Central Highlands could be 1 to 4 inches. RS

.LONG TERM...Wednesday night through Christmas Eve. Deep upper
trough drops into the area from the PAC NW Wednesday night and
should result in active weather through Thursday. The low departs to
the east, and we should see drier conditions Thursday night. A
second trough looks to drop in from the north on Friday, this one
also bringing some precip and much colder temperatures. GFS
ensembles still showing some uncertainty on how far west the trough
will extend, though deterministic guidance from GFS and ECMWF show
enough confidence to boost PoPs a bit, especially for the Central
Mountains. Saturday night and Sunday night are looking to be very
cold with overnight lows in the single digits, potentially sub-zero
in the Snake Plain. Hinsberger

&&

.AVIATION...Stratus in the Snake Plain is beginning to lift and move
up-valley. Clearing line is right over KPIH at issuance, and should
be at KIDA within a couple hours. Switch to up-valley winds at KSUN
may bring in some stratus to the terminal this afternoon. MOS
guidance suggests stratus may return again tonight to KPIH and KIDA.
Hinsberger

&&

.Air Stagnation...Some temporary improvement of air quality
today. Some low stratus may move back into the Franklin county area
on Monday. RS

&&

.PIH WATCHES/WARNINGS/ADVISORIES...None.

&&

$$



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