Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 130308 AAA
AFDPIH

Area Forecast Discussion...UPDATED
National Weather Service Pocatello ID
808 PM MST Tue Dec 12 2017

.UPDATE...Our update this evening mainly dealt with thicker cloud
cover especially the farther east you live in Idaho, and tweaking
fog and stratus a bit. We went ahead and issued a DENSE FOG
ADVISORY for a good portion of the Magic Valley. Low clouds and
fog haven`t left and we aren`t expecting it to through tomorrow
morning. It`s possible with this storm moving across the region
that it breaks up, BUT we aren`t getting too excited at this
point. Even if it did, it easily could end up being temporary. We
have freezing fog included for areas farther northeast across the
Snake Plain, but we didn`t issue any headlines for now. We will
see how far it expands over the next few hours. Keyes

&&

.PREV DISCUSSION... /issued 141 PM MST Tue Dec 12 2017/

SHORT TERM...Tonight through Friday. A ridge of high pressure
remained over the region early this afternoon as a weak Pacific
disturbance was topping the ridge and digging SE along the Canadian
Rockies. Numerical models continue to show the ridge retrograding
westward later tonight and Wednesday as the passing disturbance
clips the Island Park region. Thus have added a slight chance
mention of snowfall in that area for Wednesday. The ridge rebounds
along the coast Wednesday night before giving way to a second
incoming Pacific disturbance Friday afternoon/night. Numerical
models are about 6hrs slower than previous progs and slightly more
bullish in generating precipitation across SE Idaho than yesterdays
model runs, especially for Friday night (more on that in the Long
Term below). Daytime temps continue to gradually warm while
overnight inversions hold strong. Have tried to keep that trend
going through the Short Term with perhaps some mixing breaking into
the region Friday afternoon with the approaching disturbance. Thus
allowed a little more influence from the statistical models for
Friday afternoon. Huston

LONG TERM...Friday night through Tuesday. Snow showers are expected
Friday night into early Saturday morning resulting from a quick-
moving upper low and subsequent weak surface cold front. This is not
currently forecast to produce much in the way of snow accumulations,
with less than an inch forecast in the valleys and upwards to 3
inches above 7000 ft in the eastern Highlands. This front will only
slightly drop morning temperatures over the weekend. Our confidence
in the timing of this particular front and trough is low attm as
both have sped up in model forecast compared to yesterdays. Skies
now look to clear out during the day Saturday; continuing into
Sunday with little to no precip forecast. Early next week looks dry
as well, until the next weather system approaches later on Tuesday,
bringing snow showers to the mountains Tuesday evening. NP/MH

AVIATION...Fog is not wanting to lift out of the BYI vicinity this
afternoon and latest short-term models are not showing it lifting
this evening as well. Expect continued IFR/LIFR ceilings and
visibility here.  Fog/mist is expected to return to IDA overnight
and may return to PIH as well. Look for lowering ceilings and
visibility to IFR/LIFR in these locations. SUN and DIJ will continue
in VFR status the next 24 hours. NP/MH

AIR QUALITY...Inversions continue to hold and reduce air quality,
particularly for Franklin County where an Air Stagnation Advisory
remains in effect. Wednesday afternoon, the NAM12 model increases
winds from the north which could help scour the valley out some. RS

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM MST Wednesday for IDZ017.

&&

$$



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